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

Only gold members can continue reading. Log In or Register to continue

Related posts:

Default ThumbnailMetyrapone Stimulation Test Default ThumbnailOvine Corticotropin-Releasing Hormone (oCRH) Stimulation Test Default ThumbnailThyroid Cancer Follow-Up: Thyrogen Injection with No Scan Default ThumbnailClonidine Suppression Test Default ThumbnailCombined CRH Dexamethasone Suppression Test Default ThumbnailIntravenous Saline Suppression Test

Stay updated, free articles. Join our Telegram channel
Tags:
Sep 18, 2016 | Posted by in ENDOCRINOLOGY | Comments Off on Levothyroxine Absorption Test

Full access? Get Clinical Tree
Get Clinical Tree app for offline access