Levothyroxine Absorption Test

Precautions:
Supervise patient continuously during the procedure.
Interpretation:
Absorption is calculated by using the following formula [1]:
$$ \%\operatorname{LT}4\ absorption=[(peak\Delta \ Total/freeT4\times vd(dL)\div administered\ \operatorname{dose}\operatorname{of}\,LT4\,(\mu g)]\times 100]. $$
Volume of distribution (Vd) in deciliters: 4.42 × body mass index [1].
More than 60–80 % absorption is considered normal and rules out levothyroxine malabsorption [2, 3].

Biological Causes of Levothyroxine Malabsorption or change in metabolism or requirement [4]

Gastrointestinal Diseases
Coeliac disease
Lactose intolerance
Vitamin B12 deficiency
Intestinal infections
(Giardia lamblia)
Liver diseases such as cirrhosis
Obstructive liver disease
Pancreatic diseases—Pancreatic insufficiency
Previous gastrointestinal surgery jejunostomy
Jejunoileal bypass
Short bowel syndrome
Medication Interference
Cholestyramine
Colestipol
Aluminum hydroxide-containing antacids
Ferrous sulphate
Sucralphate
Propranolol
Laxatives
Calcium supplements
Lovastatin
Bile acid sequestrants [1].
Activated charcoal
Anion exchange resins
Phenytoin
Phenobarbital
Carbamazepine
Rifampin
Amiodarone
Oestrogen therapy
Dietary Interference
Walnuts
Soybean
Prunes
Herbal remedies
Others
Congestive heart failure
Pregnancy

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Sep 18, 2016 | Posted by in ENDOCRINOLOGY | Comments Off on Levothyroxine Absorption Test

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