A simple screening test can be used to identify patients who may have iron malabsorption.


Oral dose of iron:

(1) 325 mg ferrous sulfate (Swain et al)

(2) 100 mg of elemental iron (Cook)


NOTE: In Swain et al (1996), the authors state a 325 mg dose contains 64 mg of elemental iron. The molecular weight of ferrous sulfate is 151.91 g, with Fe 36.8% of the total. The ferrous sulfate formulation used by Swain is hydrated; according to the Merck Index it is a heptahydrate (7 water molecules).



(1) Measure the baseline serum iron level.

(2) Administer an oral dose to the patient while fasting.

(3) Measure the serum iron at 1 and 2 hours after administration.


rise in serum iron =

= MAX(1 hour post level, 2 hour post level) - (predose level)



• The baseline serum iron should be low (< 50 µg/dL).

• A fasting patient usually will show an increase of 200-300 µg/dL.

• A rise of < 100 µg/dL is suggestive of intestinal malabsorption. The next step is usually to perform a small bowel biopsy.

• Patients with a partial gastrectomy may absorb oral iron poorly if taken with food, but may absorb adequately if the iron is taken between meals.


Iron malabsorption may be seen in patients with:

(1) total gastrectomy

(2) extensive resection of the upper small intestine

(3) celiac sprue

(4) other diseases of the upper small intestine


Limitations: Drugs that interfere with iron absorption should not be given during the test. Drugs which may interfere with iron absorption include:

(1) antacids

(2) histamine-2 blockers

(3) proton pump inhibitors

(4) levodopa


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