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).
Procedure:
(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)
Interpretation:
• 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
