7. Hematology

“There are about 25 trillion red blood cells packed inside a single human body—line them side by side and they will circle the earth 15 times. This astoundingly large surface area was created to deliver what each cell in our body needs: oxygen.”

7.1 Anemia

Anemia is the state of reduced hemoglobin in blood.

Clinical pathophysiology: Presentation can vary with the degree of anemia—from exercise intolerance and easy fatigability to shortness of breath at rest. Also, with decrease in oxygen delivery to tissues, the body signals the heart to pump more blood, so there is increase in heart rate (palpitations) and increase in stroke volume (physical exam may reveal high flow midsystolic murmur in aortic area, known as a functional murmur). Additional exam findings includes scleral pallor.

  • Cardiac ischemia can develop due to increased work load (tachycardia) and increased demand for O2 while O2 content in blood is low.

    1 MCC of death in anemia is myocardial infarction.

  • In long-standing severe anemia, high output heart failure can ensue.

Work-up of Anemia

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Legend: 1st SIDx, first step in Dx; NSIDx, next step in dx; MCV, mean cell volume.

aSerum iron studies: ferritin, iron level, iron saturation, and total iron binding capacity. MCC of low MCV anemia is iron deficiency, so 1st SIDx is iron studies.

7.1.1 Microcytic Anemias (MCV < 80)

Low mean cell volume (MCV) means there is a problem with production of hemoglobin component of red blood cell (RBC).

2 Hemoglobin = heme + globin Heme = iron + protoporphyrin

• hemoglobin

• heme

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Iron Deficiency Anemia

What happens to serum iron studies in iron deficiency state?

  • Ferritin is the storage form of iron. When the body iron stores are low, serum ferritin is low.

  • Low iron stores result in compensatory increase in synthesis of transferrin. (Transferrin is a serum protein that binds and transports iron to various tissues.)

  • Increase in transferrin means increase in serum iron binding capacity.

  • As serum iron is low, the iron saturation is low. Iron saturation refers to the number of iron molecules that are bound to transferrin molecule.

Serum iron studies cofirms iron defeciency state. NSIM is to treat the iron deficiency and find the cause.

Rx: Iron replacement therapy (IV or oral) and supportive transfusion as needed. Follow-up response with reticulocyte count and iron studies.

3 If there is no response to iron supplementation, 1st SIM is to check for compliance and ask for side effects. Main reason patients do not take iron pills is because of GI upset.


  • Main etiology is bleeding.

    • Less than 50 years: likely etiology in this age group is menorrhagia in females, and peptic ulcer disease in males.

    • More than 50 years: consider colon cancer. Check fecal occult blood test and do colonoscopy.

  • Prematurity: most of the iron stores in the newborns is acquired from mother during third trimester of pregnancy.

  • In children, there is increased demand for iron, thus decreased intake of iron can easily result in iron deficiency.

    4 Cow milk is low in iron.

    In children, if there is no response to iron supplementation, gastrointestinal bleeding due to Meckel’s diverticulum is the potential cause.

  • Chronic mechanical hemolysis (e.g., in mechanical heart valve).

  • Increased demand after erythropoietin treatment in end-stage renal disease (ESRD) patients.

In a nutshell

Iron deficiency anemia

Serum ferritin


Transferrin and total iron binding capacity

Serum iron


% saturation


Clinical Case Scenarios

Iron deficiency anemia in a patient > 50 years of age.

  1. What is the 1st SIDx?

  2. What is the best SIDx?

Anemia of Chronic Disease

Etiology: Any cause of chronic inflammation such as collagen vascular diseases, active malignancy, chronic infection (e.g., chronic osteomyelitis), etc.

Pathphysiology: Increase in inflammatory mediators signal liver to produce hepcidin that blocks the release of iron from its storage form. Increased iron stores mean high serum ferritin

5 Ferritin is also a marker of inflammation. It can be high in patients with ongoing infection and/or inflammation.

leading to negative feedback for transferrin synthesis (low total iron binding capacity [TIBC]). As iron is not released from its storage form, serum iron and iron saturation is low.

Management: Treat underlying cause.

Supportive Rx: In patients with Hb < 10 g/dL, iron replacement therapy is indicated if ferritin < 100 ng/mL OR iron (transferrin) saturation < 20%. Erythropoietin-stimulating agents are given (e.g., darbepoetin) after ensuring adequate iron stores.

In a nutshell

Anemia of chronic disease

Serum ferritin

Transferrin and total iron binding capacity


Serum iron


% saturation


Sideroblastic Anemia

Pathophysiology: Inadequate or abnormal synthesis of protoporphyrin to make heme. This will result in idle iron not being used for hemoglobin synthesis (so serum ferritin, serum iron, and iron saturation is high).


  • Hereditary (congenital)

  • Alcohol

  • Vit B6 (pyridoxine) deficiency: it can be hereditary or acquired (e.g., due to isoniazid use)

  • Copper or lead poisoning

  • Clonal sideroblastosis, likely due to underlying myelodysplastic syndrome

    Diagnostic evaluation: usually history and iron study point toward the diagnosis.

Sideroblastic anemia

Serum ferritin

Transferrin and TIBC


Serum iron

% saturation

The most specific test is bone marrow biopsy with iron staining (Prussian blue stain) of specimen. In absence of protoporphyrin to complete the hemoglobin synthesis, iron dedicated for heme synthesis becomes trapped in mitochondria of erythrocyte precursors (mitochondria is where heme biosynthesis begins). This shows up like an apparent ring around the nucleus, hence called ringed sideroblasts (white arrows). Sometimes you can see stippled RBCs (basophilic stippling) on peripheral blood smear.

Some types of refractory sideroblastic anemia are associated with myelodysplastic syndrome and development of leukemia. Presence of sideroblasts along with high MCV points toward this development.

Management: Treat underlying cause.


Definition: Abnormal production of globin protein (of hemoglobin) due to hereditary genetic defect.

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Source: Microcytic hypochromic anemia. In: Siegenthaler W. Siegenthaler’s differential diagnosis in internal medicine: from symptom to diagnosis. 1st ed. Thieme; 2007.

α thalassemia is genetic defect in production of

β thalassemia is genetic defect in production of β-globin protein

Four genes are responsible for production of α-globin, so there are four levels of severity:

  • 1 gene deleted—asymptomatic

  • 2 genes deleted—mild anemia

  • 3 genes deleted—moderate to severe anemia, usually requiring blood transfusions

  • 4 genes deleted—incompatible with life and fetuses die in utero

There are two genes responsible for production of β-globin:

  • 1 gene deleted—minor degree of anemia

  • 2 gene deleted—β-thalassemia major (aka Cooley’s anemia). Severe symptoms develop 6 months after birtha

a Fetal hemoglobin does not have β-globin protein, so fetuses and newborns are not affected. After 6 months, adult hemoglobin replaces fetal hemoglobin.

Diagnostic evaluation:

  • When to suspect: Microcytic anemia with normal iron panel, and normal red cell distribution width (RDW). Peripheral blood smear shows homogenous hypochromic cells and target,

    6 When “target cells” (2) are mentioned in a test question, think of the following conditions: Hemoglobinopathies (hemoglobin C, sickle cell disease, thalassemias, etc.) Liver disease Splenectomy

    or tear drop cells(see ‘1’ on the right image).

  • NSIDx is hemoglobin assay

    7 FYI, Hb assaying methods include high-performance liquid chromatography, capillary electrophoresis, and isoelectric fusing. These newer methods are preferred over traditional gel electrophoresis.

  • Confirmatory testing includes DNA-based methods (e.g., PCR).

Hemoglobin Assay

To undestand hemoglobin assays, we need to know about different types of hemoglobin.

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  • In alpha thalassemias, there is reduced synthesis of all forms of hemoglobin. Four gamma (γ) chains can fuse to form Bart’s hemoblogin, and percentage of Bart’s hemoblogin corresponds with severity of alpha thalassemia. In 3 or 4 genes-deleted severe alpha thalassemias, excess of β chains can fuse to form β-globin tetramer (HbH).

  • In beta thalassemia, there can be compensatory increase in Hb A2 or HbF.


  • Severe anemia is treated with regular blood transfusion.

    8 This can lead to secondary hemochromatosis (iron overload) later in life. Now serum iron panel will show elevated ferritin and increased iron saturation.

  • Splenectomy can decrease the need for transfusion. Spleen is where donor erythrocytes are naturally destroyed.

Prenatal Screening for Thalassemias

Indication: pregnant patients with abnormal screening complete blood count (CBC) (low MCV with normal RDW), or in couples with positive family hx.

Test of choice is hemoglobin assay of both parents.

9 In patients with family hx of thalassemias, screening starts with CBC and peripheral blood smear.

If hemoglobin assay is negative in at least one parent, the risk of clinically important disease is low. Reassure the parents-to-be. If both are carriers, only then there is a risk of clinically important disease in the baby. Offer counseling and further prenatal diagnostic options.

Clinical Case Scenarios

3. Patient has hx of multiple RBC transfusions in the past. Hemoglobin assay shows increased HbA2 and HbF. What is the likely dx?

4. Patient with history of hypertension, dyslipidemia, diabetes, and rheumatoid arthritis is found to have anemia. TIBC and iron saturation is low and serum ferritin is high. What is the likely cause of anemia?

7.1.2 Macrocytic (MCV > 100) or Megaloblastic Anemias

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Source: Cell degradation, special granulations, and nuclear appendages in neutrophilic granulocytes and nuclear anomalies. In: Theml H, Diem H, Haferlach T. Color atlas of hematology: Practical microscopic and clinical diagnosis. 2nd ed. Thieme; 2004.

Background: Bone marrow stem cells require vitamin B12 (cobalamin) and folic acid for DNA synthesis. Deficiency of either can result in abnormal DNA synthesis and formation of large RBCs (macroytic anemia). Antimetabolite medications, such as methotrexate, phenytoin, trimethoprim, 6-mercaptopurine, can also impair DNA synthesis resulting in macrocytosis.

Work-up: If macrocytosis is seen, NSIDx is peripheral blood smear and serum folate and vitamin B12 level. Presence of hypersegmented neutrophils (≥ 5 lobes in nucleus) is pathognomonic of megaloblastic anemia.

Other notable causes of macrocytosis:

Without megaloblastosis, or hypersegmented neutrophils

Can have hypersegmented neutrophils, or megaloblastosis

  • Alcoholism

  • Liver disease

  • Hypothyroidism

  • Myelodysplastic syndrome can present with macrocytosis

  • HIV

  • Antimetabolites

Vitamin B12 Deficiency

Mechanism of vitamin B12 absorption: Vitamin B12 is released from food in presence of gastric acid. It then binds with intrinsic factor (secreted from gastric parietal cells) in the duodenum, which requires presence of pancreatic enzymes. This vitamin B12–intrinsic factor complex is absorbed by ileum into the circulation.

Etiology of vitamin B12 deficiency:

Pernicious anemia (autoimmune destruction of gastric parietal cells)

  • The MCC of vitamin B12 deficiency

  • It can be associated with other autoimmune diseases.

  • Pernicious anemia can lead to development of atrophic gastritis (loss of gastric rugae/folds and achlorhydria) and compensatory increase in gastrin level; hence it is associated with an increased risk of gastric cancer

Chronic pancreatitis with exocrine pancreatic deficiency

Decreased binding of intrinsic factor to vitamin B12

Conditions with ileal involvement

Ilectomy, Crohn’s disease, tropical sprue, etc.

Strict vegan diet for more than 3 years

Vitamin B12 deficiency can develop in a completely vegetarian patient (no dairy products or eggs); but note that it takes at least few years for the body stores of vitamin B12 to be depleted

No gastric acid (achlorhydria)

Gastrectomy or long history of proton pump inhibitors use (> 3 years)

Fish tapeworm (Diphyllobothrium latum) infection

Risk factor: people who consume raw fish (including sushi and sashimi)

Additonal manifestation (neurological symptoms): Vitamin B12 deficiency can result in excessive production of methylmalonic acid, which is toxic to myelin sheath leading to demyelination. Patients may develop decreased position and vibratory sense. Glove stocking peripheral neuropathy is common, but note that any nervous system can be involved (autonomic neuropathy, motor paralysis, cranial nerves involvement, dementia, etc.)

Diagnostic Evaluation

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aIf patient does not have an obvious cause of deficiency such as hx of ilectomy or being a complete vegeterian for > 3 years.

Treatment: Oral or intramuscular vitamin B12 supplementation. In patients with significant anemia, neurological symptoms, or pernicious anemia, start intramuscular vitamin B12 injections.

10 Parenteral vitamin B12 treatment can result in hypokalemia due to rapid uptake of potassium by newly forming hematopoietic cells.

Otherwise, oral vit B12 can be given.

Schilling Test

Even though it is not used for diagnosis nowadays, it is asked on exam, as it requires knowledge of mechanism of vitamin B12 absorption.

How it is performed: Intramuscular vitamin B12 is first given to saturate all the serum vitamin B12 receptors. Next step is oral administration of radiolabeled (RL) vitamin B12. If absorption is intact, the absorbed RL vitamin B12 will be directly excreted with urine (as there are no seats left to bind in receptors).

  • If urinary excretion of RL (radio-labeled) vitamin B12 is high, then the deficiency is related to poor intake.

  • If urinary excretion of RL vitamin B12 is low, then NSIDx is to add intrinsic factor to oral RL vitamin B12.

    • If urinary excretion is high, dx of intrinsic factor deficiency is made.

    • If urinary excretion is still low, then other dx that can be considered are pancreatitis (test normalizes after pancreatic enzyme supplementation), bacterial overgrowth (normalizes when the test is repated after a trial period of empiric antibiotic therapy), etc.

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Folate Deficiency




Additional info

Alcoholism (MCC in the United States)

Alcohol blocks absorption of folate

Antiepileptics (phenytoin, primidone and phenobarbital, carbamazepine)

These drugs block absorption of folate from GI tract.

Methotrexate, trimethoprim, pyrimethamine

Mechanism: inhibits dihydrofolate reductase

  • Patients taking one of these medication for long term need leucovorin (aka folinic acid, which is reduced folate) for prophylaxis

Chronic hemolysis

Body’s folate stores can be readily depleted (e.g., in sickle cell anemia, spherocytosis)

Increased requirements

For example in pregnancy

Low dietary intake

  • Infants fed with goat milk which is low in folate

  • Diet low in fresh vegetables, fruits, or meat (e.g., tea-and-toast diet, typically elderly or psychiatric patients)

Treatment: Replace folate (almost always orally, because the MCC of folate deficiency is due to decreased intake or absorption).

In a nutshell

Vitamin B12 and Folate Deficiency

  • Homocysteine can be elevated in both.

  • Both can cause mild hemolysis (elevated lactate dehydrogenase [LDH] and elevated bilirubin) and pancytopenia, if severe. (The abnormally large blood cells get destroyed).

  • Only vitamin B12 deficiency can have elevated methymalonic acid level and neurological manifestation.

7.1.3 Normocytic Anemia (MCV 80–100)

Normal MCV means that there is no problem in hemoglobin or DNA synthesis. This anemia can be due to the following:

  • Increased destruction of RBCs (hemolytic anemias): look for high peripheral reticulocyte count (there is compensatory increased RBC production).

  • Decreased production of RBCs (primary bone marrow pathology): low reticulocyte count.

7.1.4 Hemolytic Anemia

Intravascular hemolysis

Extravascular hemolysis


  • Production of IgM antibody against RBC, aka cold agglutinins. IgM antibodies are potent activators of the complement system, so destruction occurs inside blood vessels

  • Physical destruction of RBCs moving past calcified aortic valves, metallic prosthetic valves, or thrombi

    • Acute process occurs in states of generalized clot formation, for example, TTP/HUS or DIC

    • Chronic process (e.g., metallic prosthetic valves) may lead to chronic hemolysis and chronic hemoglobinuria. This may lead to iron deficiency or folate deficiency anemia

  • Hereditary deficiency in one of the enzymes involved in glycolytic pathway leads to increased sensitivity of RBCs to oxidative stress (e.g., pyruvate kinase or glucose-6-phosphate dehydrogenase deficiency)

  • Paroxysmal nocturnal hemoglobinuria


RBCs are being gobbled up by the splenic macrophages, but why?

  • The RBCs with attached IgG (in warm autoimmune hemolytic anemia) activate phagocytic process of macrophages. IgG are less potent activators of complement system so there is no intravascular hemolysis, but macrophages in splenic sinusoids have IgG receptors which will recognize it and destroy the RBC

  • The RBCs cannot enter the narrow splenic sinusoids because their biconcave shape to squeeze in is lost,such as in hereditary spherocytosis, hereditary elliptocytosis

  • Physiologic: old RBCs, usually after about 3 months, start losing their membrane flexibility, hence they cannot squeeze in through the splenic sinusoids and are subsequently eaten up by splenic macrophages

Abbreviations: DIC, disseminated intravascular coagulation; HUS, hemolytic uremic syndrome; IgM, immunoglobulin M; RBC, red blood cells; TTP, thrombotic thrombocytopenic purpura.

Diagnostic work-up: To find out whether RBCs are being destroyed in the blood vessels (intravascular hemolysis) or the spleen (extravascular hemolysis), do the following tests: peripheral blood smear, Coomb’s test, serum LDH, haptoglobin, and bilirubin levels.





Normal or low


Can be presenta


LDH (spill over of LDH from RBCs )

Normal or ↑

Indirect bilirubinb




aWhen RBCs are destroyed intravascularly, hemoglobin is released directly into blood stream. There is a protein named haptoglobin that binds to free hemoglobin in blood and transports it to spleen. Low haptoglobin levels are indicative of intravascular hemolysis. In severe acute hemolysis, there is not enough haptoglobin to sequester excessive hemoglogbin, which ends up being filtered by kidneys (hemoglobinuria). This can be toxic to renal tubular cells, causing acute tubular necrosis and renal failure. Moreover, some of this hemoglobin gets oxidized to hemosiderin resulting in hemosiderinuria. Patients may have gross red-/tea-/cola-colored urine. Urine dipstick test is positive for blood but no RBCs are seen in microscopy.

11 Urine dipstick test detects globin protein—hemoglobin (either free or inside RBCs) or myoglobin.

bPatients with chronic hemolysis have increased risk of calcium bilirubinate gallstones formation. Abbreviation: LDH, lactate dehydrogenase.

Autoimmune Hemolytic Anemia


Cold autoimmune hemolytic anemia (IgM antibody)

Warm autoimune hemolytic anemia (IgG antibody)


  • Mycoplasma pneumonia

  • EBV infection (infectious mononucleosis)

  • Isoagglutinins: people with blood type O have IgM antibody against A and B antigens; transfusion of type A, B, or AB to type O patient will cause intravascular hemolysis. Likewise, people with blood type B have IgM antibody against A, and blood type A have IgM antibody against B

  • Quinidine—an antiarrhythmic drug

  • Lymphomas

  • Waldenstrom’s macroglobunemia

  • Causes:

  • SLE

  • Drugs that can induce SLE-like condition:

  • Chlorpropamide, Hydralazine, Isoniazid, Methyldopa, Procainamide, Quinidine, etc.

  • Hemolytic disease of the newborn (only IgG can cross the placental barrier; IgM cannot)

  • Chronic lymphocytic leukemia

  • Lymphomas

Direct Coomb’s test is positive with following reagenta



Additional test

Cold agglutinin titer is the most accurate test

  • Peripheral blood smear may show presence of spherocytes

  • The spherocytes have increased osmotic fragility (splenic macrophages bite off pieces of RBC membrane, resulting in loss of its surface area)


  • Avoidance of cold temperature

  • May use rituximab +/- fludarabinec

  • If severe and acute, plasmapheresis can be done

  • Corticosteroids and if refractory, splenectomyd

  • If severe and acute, IVIG can be givene

aDirect and indirect Coomb’s (antiglobulin) agglutination test.


bIgM antibodies are powerful activators of complement. In cold auto-immune hemolytic anemia, complement proteins are bound to RBCs.

cOther immunosuppressive agents that can be used are azathioprine, cyclosporine, and cyclophosphamide.

dIn IgG-type autoimmune condition, blood cell destruction takes place in spleen.

eTreatment is similar to other IgG-mediated diseases (e.g., immune thrombocytopenia).

Abbreviations: EBV, Epstein-Barr virus; IgG, immunoglobulin G; IgM, immunoglobulin M; IVIG, intravenous immunoglobulin; SLE, systemic lupus erythematosus.


CHIMP queen has SLE

Hereditary Spherocytosis

Normal blood

Spherocytosis (Note absence of central pallor in a lot of RBCs)

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Source: Anemia. In: Siegenthaler W. Siegenthaler’s differential diagnosis in internal medicine: from symptom to diagnosis. 1st ed. Thieme; 2007.

Background: It is mostly of autosomal dominant inheritance. It is due to genetic defect of structural proteins that are involved in giving the biconcave shape to RBCs. One of the commonly involved protein is called spectrin.

Pathophysiology: RBCs in this disorder are spherocytic, they cannot squeeze through the splenic sinusoids and are subsequently eaten up by splenic macrophages. These patients have chronically elevated bilirubin (due to chronic hemolysis), which in turn increases the risk of calcium bilirubinate gallbladder stones formation.

When to suspect: Features of extravascular hemolytic anemia with positive family hx, +/- biliary colic. Spherocytes are seen in peripheral blood smear and direct Coomb’s test is negative. Work-up: Best screening test is eosin-5-maleimide binding test (a flow cytometric test). If this is not available, other tests that can be done are osmotic fragility test, acidified glycerol lysis time test, or the cryohemolysis test.

Management: Oral folate replacement and transfusions as required. If moderate to severe anemia, splenectomy can be done (remove the organ where the RBCs are being destroyed).

How to differentiate between autoimmune IgG hemolytic anemia and hereditary spherocytosis?

Autoimmune IgG type

Hereditary spherocytosis

Extravascular hemolysis



Spherocytes in peripheral blood smear



Osmotic fragility (RBCs are more fragile to osmotic swelling)

Positive Coomb’s test



Family hx




SAD Spherocytes

Glucose-6-Phosphate Dehydrogenase Deficiency

Background: This is an X-linked recessive

13 X-linked recessive disorders manifest in male patients. Females are carriers.

hereditary disorder with deficiency of glu-cose-6-phosphate dehydrogenase (G6PD), which is a powerful antioxidant in RBCs. In patients of African American descent, it usually presents in a milder form, whereas patients of Mediterranean descent have more severe form.

Precipitating factors: Acute intravenous hemolysis occurs whenever there is an increased oxi-dative stress:

  • Any infection (MC precipitaing factor).

  • Drugs: sulfamethoxazole, primaquine, quinine, dapsone, isoniazid,

    14 Isoniazid + anemia: think of G6PD deficiency (when acute) or sideroblastic anemia (when presentation is insidious)

    Thrombosis is the MCC of death in paroxysmal nocturnal hemoglobinuria (PNH).

    nitrofurantoin, etc.

  • Fava beans.


During an acute episode

Peripheral blood smear with Heinz stain (methylene blue stain): This will show Heinz bodies +/- bite cells.

  • Heinz bodies are oxidized hemoglobin in in RBCs. These can get bitten off by splenic macrophages, leaving behind bite cells.

No Image Available!

Source: Anemia. In: Siegenthaler W. Siegenthaler’s differential diagnosis in internal medicine: from symptom to diagnosis. 1st ed. Thieme; 2007.

When patients do not have an acute episode of hemolysis

Dx is made by G6PD enzyme assay

(Enzyme assay can be deceivingly normal in an acute epiosde, as the RBCs with low enzyme would have already died off, leaving behind only the RBCs with normal enzyme.)

Rx: Supportive transfusion during an acute episode, treat underlying problem and avoid oxidant stress.

Paroxysmal Nocturnal Hemoglobinuria

Background: It is due to hereditary genetic defect in red cell membrane protein—phosphatidy-linositol glycan (PIG-A), aka decay-accelerating factor (proteins CD55 and CD59). This leads to easy binding of complement system to the red cell causing intravascular lysis of RBC, especially in acidic environment. This disorder is also associated with increased risk of varying degree of bone marrow failure (causing pancytopenia) and myelodysplastic syndrome.

Clinical pathophysiology: Nocturnal hemolysis can occur due to development of mild acidosis related to sleep-induced hypoventilation. Patients may present with early morning red urine. Hemolysis can also develop after exercise.

Along with acute hemolysis, patients also have increased risk of venous thrombosis, especially in uncommon locations such as hepatic vein or cerebral vein. Arterial thombosis has also been reported.

Work-up: NSIDx is flow cytometry, which will show absent or reduced expression of CD55/CD99. Older methods of detection are acidified hemolysis test (Ham’s test) and sugar water test (sugar is metabolized by RBCs into lactic acid).


  • Supportive: Blood transfusion as needed and iron/folate supplementation.

  • For ongoing hemolysis, prednisone (steroids) might be helpful.

  • For patients with significant disease, give eculizumab (monoclonal antibody that inhibits complement activation).

  • In patients with severe disease, bone marrow transplantation can be done.

7.1.5 Sickle Cell Anemia

Background: It occurs due to single nucleotide (point) mutation in β-globin gene. This mutation replaces the amino acid glutamate (which is hydrophilic) with valine (which is hydrophobic) in the sixth position of β-globin protein. This change of a single amino acid increases risk of change in RBC shape, from biconcave to sickle shaped, whenever the hemoglobin is relatively desaturated. These sickled cells can clump together and easily get stuck in the vessels, obstructing the blood flow, thus causing infarction in various organs.

Factors that promote sickling and precipitate sickle cell crisis

Example clinical scenario where it occurs

Relatively higher concentration of sickle cells promotes sickling of RBCs


Low oxygen saturation due to hypoxia

Pneumonia, pulmonary embolus, exposure to high altitude, etc.

Any condition that decreases the affinity of hemoglobin for oxygen (conditions that cause right shift in Hb-O2 dissociation curve)

  • Acidosis

  • CO2 elevated—hypercarbia increases acid (H+) content in blood

  • Temperature elevation (fever)

  • Elevated Diphosphoglycerate (2,3-DPG)


For acute presentation, NSIDx is peripheral blood smear to look for sickled cells. To make the definitive diagnosis, use hemoglobin assay.

15 Hb assay is also used for screening relatives of the patient.

Hb assay


> 40% HbS

Sickle cell disease

< 40% Hbs

Sickle cell traita

a Most of the time, patients with sickle cell trait are asymptomatic or can have minor renal manifestations such as microscopic or macroscopic hematuria and/or isosthenuria.

16 Isosthenuria is loss of concentrating or diluting ability of kidney that results in urine having the same specific gravity as plasma. (Iso = same)

Abbreviation: Hbs, hemoglobin sickle.

Acute presentation of sickle cell disease (acute anemia and acute painful crises)

7.1.6 Acute Anemia in Sickle Cell Disease

NSIDx is CBC, reticulocyte count and peripheral blood smear.


Peculiar PNH can cause venous and arterial thrombosis and is treated with eculizumab.



High reticulocyte count

Splenic sequestration crisis: Sickled cells are stuck and pooled in spleen. This doesn’t occur in patients who have fibrotic spleen.

Look for sudden splenomegaly, abdominal pain +/- systemic hypotension (not only the RBCs, the whole blood pools in spleen)

Hemolytic crisis with component of both intravascular and extravascular hemolysis. This can occur in conjunction with acute painful crisis

Low reticulocyte count

There are two possible causes:

  • Parvovirus B19 infection (acute aplastic crisis or pure red cell aplasia)

  • Folate deficiency

Rx: is supportive with RBC transfusion as needed and treatment of underlying cause.

Acute vaso-occlusive sickling crisis

Acute clumping of sickled RBCs in the arteries and arterioles can cause ischemia/infarction. Depending on location, it can present with the following:

Acute chest syndrome

Chest pain, fever, leukocytosis, hypoxia, and infiltrates on chest X-ray. It is clinically indistinguishable from pneumonia


Painful prolonged erection +/- penile infarction


Sickling in vessels of the hands and feet can cause, severe pain in distal extremities, i.e., painful hand and foot syndrome (infarction in the hands and toes)

Visual problems

Sickling in the retinal vessels causing retinal artery occlusion

Stroke (ischemic or hemorrhagic)

Acute focal neurological deficits

Renal infarction

Hematuria, acute renal failure, etc.

Avascular necrosis of femoral head

Hip pain

Stepwise management of acute vaso-occlusive sickling crisis

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aPain management with opioid analgesics is an important part of management.

bTransfusion can be either simple RBC transfusion or exchange transfusion. Exchange transfusion is when sickle cells are filtered out and normal RBCs are transfused in exchange (remove blood and then give blood back).

Exchange transfusion indications

RBC transfusion

  • Multiorgan failure

  • CNS abnormalities like confusion (altered mental status) and focal neurological deficits

  • Moderate to severe acute chest syndrome

  • Acute cardiac manifestations

  • Refractory priapism

Only preferred in patients with severe symptomatic anemia (Hb < 5)

  • This decreases sickle cell concentration without increasing blood viscosity

Does not decrease sickle cell concentration by that much and can actually increase blood viscosity in patients with baseline hemoglobin levels.

Other Presentations of Sickle Cell Disease

  • Calcium bilirubinate gallstones.

  • Osteomyelitis—MCC is Staphylococcus aureus (!).

  • Pulmonary hypertension.

  • Nephrogenic diabetes insipidus.

Chronic/Preventive management of patients with sickle cell disease

  • Within the first 3 months of age, prophylactic penicillin is initiated and continued until age 5. After this, decision to continue prophylaxis is made on a case-by-case basis.

  • All patients with underlying chronic hemolysis should be on oral folate therapy.

  • In symptomatic patients, hydroxyurea is recommended. Hydroxyurea increases production of HbF and decreases production of HbS, thus decreasing risk of sickling crisis.

  • Functional asplenia: By the time patients reach late childhood, they usually have fibrosed spleen due to recurrent splenic infarction (rightly called autosplenectomy). So, all patients with sickle cell disease should receive prophylaxis indicated in asplenia.

In a nutshell

Vaccination and antibiotic prophylaxis for patients with splenectomy or functional asplenia

Vaccination: Spleen plays important role in immune defense against encapsulated microorganisms. Patients undergoing splenectomy, or with functional asplenia should be vaccinated against the following organisms:

Streptococcus pneumoniae

  • First dose: PCV13 once, followed by PPSV 23

  • Second dose: Repeat PPSV23 after 5 years of first dose

  • Third dose: PPSV23 at age 65 or more (always maintain 5-year interval)

Neisseria meningitidis

Booster dose q5 years

Haemophilus influenzae

One dose

In patients underoing splenectomy, administer vaccination either 2 weeks prior to surgery (preferred), or 2 weeks after the surgery

Antibiotic prophylaxis:

  • Asplenic children receive daily oral penicillin prophylaxis for at least 1 year or until age of 5, whichever is later. Elective splenectomy (e.g., for treatment of hereditary spherocytosis) is usually deferred until age 6, but if needed due to severe anemia, partial splenectomy can be done earlier.

  • In adults, antibiotic prophylaxis is not recommended.

Peripheral blood smear findings in asplenia:

No Image Available!

Source: Erythrocyte inclusions. In: Theml H, Diem H, Haferlach T. Color atlas of hematology: Practical microscopic and clinical diagnosis. 2nd ed. Thieme; 2004.

  • Howell-Jolly bodies are remnants of nuclear material inside of RBCs (black arrow).

  • Target cells (red arrow)

Clinical Case Scenarios

5. Patient with hx of intermittent cola-colored urine presents with history of right upper quadrant (RUQ) pain usually after eating. What is the likely dx?

6. Patient develops abdominal pain and jaundice in the setting of 3-day history of fever and increased frequency of urination. CBC reveals acute anemia and elevated bilirubin. Urine analysis (UA) is positive for dipstick blood but no RBCs are seen microsopically. What are the differential dx?

7. African American man presents with hx of long-standing asymptomatic gross and microscopic hematuria. CT abdomen reveals no renal or urologic issues. What is the NSIDx?

In a nutshell

In all chronic hemolytic anemias (i.e., sickle cell disease, thalassemias, chronic autoimmune hemolytic anemia, hereditary spherocytosis, etc.), if there is acute anemia with low reticulocyte count, think of the following:

  • Acute folate deficiency: all patients with chronic hemolysis should be on oral folate replacement.

  • Parvovirus B19 infection: can cause acute aplastic crisis (pancytopenia) or pure red cell aplasia (only anemia).

Work-up: If folate is normal, consider testing for parvovirus B19 IgM antibody and PCR.

7.1.7 Normocytic Anemia with Zero or Low Reticulocytic Count

In this case, bone marrow is not producing new RBCs. In anemic patients with low reticulocyte count and no obvious cause,

17 Normocytic anemia with reduced reticulocyte count can develop due to following conditions:

• Advanced chronic kidney disease leads to erythropoietin (epo) deficiency. (Epo stimulates marrow stem cells to produce RBCs.)

• Advanced age.

• Anemia of chronic disease.

• Severe medical illness (e.g., severe alcoholism, endocrine disease, infection, etc.).

• Deficiency of raw materials needed to make RBCs (iron, folate, or vitamin B12 deficiency).

In these cases, if no other features of bone marrow disorder are present, bone marrow biopsy can be deferred.

or in patients with features worrisome for bone marrow disorder (e.g., pancytopenia or increased blasts in peripheral blood smear), NSIDx is bone marrow biopsy.

Bone marrow biopsy findings


Absent or reduced stem cells in the marrow which involves all cell lineage

Aplastic anemia

Only RBC stem cells are absent or reduced

Pure red cell aplasiaa

Overcrowding of bone marrow space with dysplastic or cancerous malignant cells

Myelodysplastic syndrome, leukemias,

aThis is associated with parvovirus infection and thymoma. Congenital form of pure cell aplasia is Blackfan-Diamond syndrome (look for skeletal abnormalities).

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Dec 11, 2021 | Posted by in HEMATOLOGY | Comments Off on 7. Hematology

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