Anemia in Rheumatoid Arthritis: Expected Laboratory Findings
In a 40-year-old woman with rheumatoid arthritis and hemoglobin of 9.1 g/dL, you would most likely find elevated inflammatory markers (ESR and CRP), low or low-normal ferritin (30-100 μg/L), low transferrin saturation (<20%), and possibly elevated platelet count, consistent with a mixed picture of anemia of chronic disease and iron deficiency. 1
Key Laboratory Findings to Expect
Inflammatory Markers
- Elevated ESR and CRP are nearly universal in RA patients with anemia, with CRP being the strongest predictor of anemia after ESR 2
- Approximately 98% of RA patients with active disease demonstrate elevated inflammatory markers 1
- These markers help distinguish between pure iron deficiency and anemia of chronic disease 1
Iron Studies: The Critical Distinction
Ferritin interpretation depends entirely on inflammation status:
- Ferritin 30-100 μg/L suggests a combination of true iron deficiency and anemia of chronic disease, which is the most common scenario in RA 1
- Ferritin >100 μg/L with transferrin saturation <20% confirms anemia of chronic disease 1
- Ferritin <30 μg/L (rare in active RA) indicates pure iron deficiency 1
Important caveat: Ferritin acts as an acute-phase reactant in RA, so levels up to 100 μg/L may still represent iron deficiency despite appearing "normal" 1
Complete Blood Count Findings
- Normocytic or microcytic anemia (MCV may be normal or low) 1
- Elevated RDW (red cell distribution width) indicating mixed cell populations 1
- Thrombocytosis (elevated platelet count) correlates with active inflammation and iron deficiency 3
- Low reticulocyte count indicating inadequate bone marrow response despite anemia 4
Additional Expected Findings
- Transferrin saturation <16-20% is common in both iron deficiency and anemia of chronic disease 1
- Elevated soluble transferrin receptor (sTfR) occurs in 26% of RA patients and indicates functional iron deficiency 3
- Low hepcidin (below 14.5 ng/ml) found in 56% of RA patients, reflecting altered iron regulation 3
Prevalence Context
Research demonstrates that anemia occurs in 31.5% of RA patients overall, with severe anemia (hemoglobin <10 g/dL) in only 3.4% 2. In your patient with hemoglobin of 9.1 g/dL, this represents moderately severe anemia requiring thorough evaluation. Studies show that 60-70% of RA patients develop anemia, with approximately half having iron deficiency anemia and half having anemia of chronic disease 5, 3.
Clinical Algorithm for Interpretation
Step 1: Check ESR and CRP to confirm active inflammation 2
Step 2: Obtain complete iron panel (ferritin, transferrin saturation, serum iron, TIBC) 1
Step 3: Interpret ferritin in context of inflammation:
- If ferritin 30-100 μg/L → mixed iron deficiency and anemia of chronic disease 1
- If ferritin >100 μg/L with TSAT <20% → anemia of chronic disease 1
- If ferritin <30 μg/L → pure iron deficiency (investigate GI blood loss) 1
Step 4: Check MCV and RDW to assess red cell morphology 1
Step 5: Obtain reticulocyte count to evaluate bone marrow response 4
Common Pitfalls to Avoid
Do not rely on ferritin alone in the setting of active RA, as inflammation falsely elevates ferritin levels, masking true iron deficiency 1. A ferritin of 50-80 μg/L that appears "normal" may actually represent significant iron deficiency in an RA patient with elevated CRP.
Do not assume microcytosis is required for iron deficiency diagnosis in RA—many patients have normocytic anemia with mixed pathology 1.
Do not overlook renal function, as creatinine clearance is approximately 10 ml/min lower in RA patients compared to controls and contributes to anemia 2.
The correlation between disease activity (measured by DAS-28) and anemia severity is strong, with higher disease activity scores predicting lower hemoglobin levels 5. Your patient's fatigue likely reflects both the anemia and active RA disease.