Priority Topic: Anemia

Key Feature 3: In all patients with anemia, determine the iron status before initiating treatment. 
Skill: Clinical Reasoning
Phase: Investigation, Diagnosis

In follow-up to my previous post on the assessment of anemia, if a patient is found to have  iron-deficiency anemia, it is important to determine the iron status before initiating treatment in order to be able to monitor the response to therapy. And of course, it is important to work up the cause of the iron-deficiency if it is not already apparent. 

Baseline labs that you want to have include CBC, ferritin, TIBC, and reticulocyte count, which you would likely have already given that you came to the conclusion that the patient was iron deficient. 

The exception to this would be, as I quoted UpToDate in my previous post, when children less than 2 years of age present with a microcytic anemia with a history that supports a diagnosis of dietary deficiency. In this case you may presume that the anemia is secondary to iron deficiency and begin treatment, because common things are common.

After you've started your choice of iron supplementation and recommended associated dietary suggestions (particularly in pediatric patients), you will then need to monitor response to treatment. For both children and adults:

• Monitoring oral iron supplementation involves assessing for side effects and associated compliance to taking the supplementation as prescribed, along with reassessing the CBC, ferritin, +/- TIBC, and reticulocyte count 2 weeks after starting treatment. Oral iron is notorious for side effects that include nausea and constipation.
• Reticulocyte count should peak about 7-10 days after treatment has begun, so having patients get their bloodwork done at least 1 week after starting treatment works well and the results should be back to you before their follow-up appointment 2 weeks after starting treatment.
• If the patient is instead treated with IV iron, then you wouldn't repeat bloodwork for reassessment until 1-2 months after the infusion, as the iron infusion makes the iron studies all wonky (something medical like that). But when it is time to repeat bloodwork after 1-2 months, you would run the same investigations as per oral iron supplementation
• If there is a positive response to iron supplementation, then continue therapy and reassess with a CBC and ferritin in 3 months. 

If there is a poor response to iron supplementation, then you need to consider why. Reasons to consider include:

• Poor compliance (often because of side effects)
• Poor absorption in the setting of oral iron supplementation
  • If there is no obvious explanation for this, then consider investigations for H. pylori and/or celiac disease, both of which can impair oral iron absorption in the gastrointestinal tract
• Blood loss that is exceeding the rate of iron replacement
• Wrong initial diagnosis (hopefully my approach to diagnosing iron deficiency anemia mitigates this one, but it is still a possibility - iron studies can be wonky after all)
• The diagnosis of iron deficiency anemia was correct, but maybe there is more than one reason for the anemia (especially something to consider in elderly patients)
• An acute inflammatory state (the body has a natural response to decrease iron absorption from the gastrointestinal tract when there is an acute inflammatory process going on in the body)
• Maybe the therapy was effective but then the patient re-bled or sustained some other insult that led to a decrease again in the iron stores.

In any case, you may want to just consider switching to IV iron therapy and be done with it. There are pros and cons to choosing to supplement iron by mouth or intravenously. UpToDate has a great table that contrasts the pros and cons of these choices:

Patients who you will likely want to consider giving IV supplementation to right off the get-go include, for various reasons:

• Pregnant women
• Patients with inflammatory bowel disease
• Patients with chronic kidney disease
• Patients who have had gastric surgery

(I won't get into to the nitty-gritty about what exactly to choose for iron supplementation, as there are many choices and there doesn't seem to be a gold standard as to the best way to replace iron.)