What are the characteristic findings on a complete blood count (CBC) in patients with long Covid suspected of having anemia of chronic disease?

CBC Findings in Anemia of Chronic Disease During Long COVID

In patients with long COVID suspected of having anemia of chronic disease, the CBC will typically show normocytic normochromic anemia with normal or elevated serum ferritin levels (>100 μg/L) and low transferrin saturation (<20%). 1

Key CBC Findings

Red Blood Cell Parameters:

• Hemoglobin: Decreased (<13 g/dL for men, <12 g/dL for women) 1
• MCV (Mean Corpuscular Volume): Usually normal (normocytic) 1
• MCH (Mean Corpuscular Hemoglobin): Normal or slightly decreased 1
• RDW (Red Cell Distribution Width): May be elevated 2
• Red Blood Cell Count: Lower compared to moderate cases 2

Iron Studies:

• Serum ferritin: Elevated (>100 μg/L) due to inflammatory state 1
• Transferrin saturation: Decreased (<20%) 1
• Serum iron: Decreased 3
• Transferrin: Decreased levels, with continuous decline observed in severe cases 4

Other CBC Findings:

• Reticulocyte count: Low or "normal" indicating inability to respond properly to anemia 1
• White blood cells: May show lymphopenia (reduced lymphocyte count) 3

Distinguishing Features from Other Anemias

Differentiating from Iron Deficiency Anemia:

• In pure iron deficiency anemia: serum ferritin <30 μg/L
• In anemia of chronic disease: serum ferritin >100 μg/L
• In mixed picture (both conditions): serum ferritin 30-100 μg/L 1

Time Course in Long COVID:

• Anemia prevalence increases with disease duration, reaching up to 87.8% in patients hospitalized for two weeks 4
• The anemia phenotype may shift over time from predominantly anemia of inflammation in early post-acute phase toward iron deficiency anemia in later stages 5

Clinical Correlation

The anemia pattern in long COVID reflects the underlying chronic inflammatory state, with:

• Impaired iron utilization despite adequate stores
• Decreased erythropoiesis due to inflammatory cytokines
• Possible impaired oxygen binding to hemoglobin 3
• Association with hyperinflammation markers 4

Monitoring Recommendations

1. Complete blood count with MCV, reticulocytes, serum ferritin, transferrin saturation, and CRP 1
2. Consider more extensive workup including vitamin B12, folic acid, haptoglobin, and differential white blood cell count if diagnosis remains unclear 1
3. Monitor hemoglobin trends, as declining levels correlate with disease severity 4
4. Evaluate reticulocyte response to assess bone marrow function 6

Pitfalls to Avoid

• Don't assume all anemia in long COVID is due to iron deficiency; check ferritin and transferrin saturation to distinguish between anemia of chronic disease and iron deficiency anemia 1
• Avoid premature iron supplementation without confirmed iron deficiency, as it could mask underlying conditions 6
• Remember that HbA1c interpretation should be cautious in patients with anemia 6
• Be aware that anemia in long COVID is mainly driven by inflammation, and resolution of infection typically results in normalization of dysregulated iron homeostasis 4

The pattern of anemia in long COVID reflects the complex interplay between inflammation, iron metabolism, and erythropoiesis, with normocytic anemia and elevated ferritin being the hallmark findings on CBC.