Iron Deficiency Can Cause Leukopenia, Though It's Uncommon
Yes, iron deficiency can cause low white blood cell count (leukopenia), though this is an infrequent manifestation that occurs in approximately one-third of iron deficiency anemia cases, and it typically resolves with iron replacement therapy 1.
The Evidence for Iron Deficiency-Associated Leukopenia
The relationship between iron deficiency and leukopenia is well-documented but often overlooked:
Classic presentation: About one-third of patients with iron deficiency anemia present with mild leukopenia alongside the typical microcytic, hypochromic anemia 1. This can manifest as neutropenia, lymphocytopenia, or both.
Reversibility is key: The most compelling evidence comes from case reports demonstrating complete resolution of chronic leukopenia after iron supplementation. One notable case involved a 67-year-old woman with 16 years of unexplained chronic neutropenia (diagnosed as "chronic idiopathic neutropenia") that completely resolved after 2.5 months of consistent oral iron therapy 2. This suggests that some patients labeled with chronic idiopathic neutropenia may actually have unrecognized iron deficiency-induced neutropenia.
Severe cases can present with pancytopenia: In more extreme presentations, severe iron deficiency can cause pancytopenia (low counts of all blood cell lines). A 12-year-old girl with profound iron deficiency (ferritin 1 μg/L) presented with hemoglobin 3.3 g/dL, WBC 3.9×10⁹/L, and platelets 47×10⁹/L—all of which completely normalized after six months of oral iron supplementation 3.
Clinical Implications and Pitfalls
Common pitfall: Patients with unexplained chronic leukopenia or neutropenia may undergo extensive workups for primary hematologic disorders when the underlying cause is simply untreated iron deficiency. Always check iron studies (ferritin, transferrin saturation, serum iron) in patients with unexplained leukopenia before pursuing more invasive investigations.
Important caveat: The British Society of Gastroenterology guidelines 4 focus extensively on iron deficiency anemia but do not specifically address leukopenia as a manifestation. This reflects that while leukopenia occurs, it's not the primary concern—anemia and its consequences on morbidity and mortality take precedence.
Paradoxical Effect of Iron Therapy
Interestingly, iron therapy itself can occasionally cause transient leukopenia:
Intravenous iron therapy caused leukopenia in 1.91% of 1,567 women treated for IDA, with neutropenia in 0.95% and lymphocytopenia in 0.76% 5. However, this was clinically insignificant—only 6.66% of those who developed leukopenia had infections, and these were minor.
Oral iron therapy has also been reported to cause neutropenia in isolated cases 6, though this appears even rarer than with IV iron.
Practical Approach
When encountering a patient with both iron deficiency and leukopenia:
Confirm iron deficiency: Ferritin <15 ng/mL (or <100 ng/mL in inflammatory conditions), low serum iron, elevated transferrin, decreased transferrin saturation 1, 7
Treat the iron deficiency: Oral iron supplementation is first-line unless contraindicated. The leukopenia should resolve within 2-6 months if iron deficiency is the cause 2, 3
Monitor response: Recheck CBC after adequate iron repletion. If leukopenia persists despite normalized iron stores, then pursue alternative diagnoses
Don't delay treatment: The leukopenia associated with iron deficiency appears to have minimal clinical significance in terms of infection risk, so iron replacement should not be withheld due to concerns about the low WBC count
The key message: Iron deficiency-induced leukopenia is real, reversible, and often misdiagnosed as a primary hematologic disorder. Always consider and correct iron deficiency before pursuing extensive workups for unexplained chronic leukopenia.