Laboratory Workup for Suspected Anemia in Adults
Initial Essential Laboratory Tests
Order a complete blood count (CBC) with differential, reticulocyte count, serum ferritin, transferrin saturation (TSAT), vitamin B12, and folate levels as your initial anemia workup. 1
Core Panel Components
- CBC with differential and red cell indices: Provides hemoglobin concentration, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), white blood cell count with differential, and platelet count 1
- Absolute reticulocyte count: Critical for determining if bone marrow is responding appropriately—low/normal suggests deficiencies or marrow failure, while elevated indicates hemolysis or acute blood loss 1, 2
- Serum ferritin: Single most useful marker for iron deficiency, though can be falsely elevated in inflammation 1
- Transferrin saturation (TSAT): Essential when ferritin is equivocal or elevated due to inflammation; TSAT <20-30% indicates functional iron deficiency even with normal/high ferritin 1, 2
- Vitamin B12 and folate levels: Mandatory to exclude macrocytic causes that may be masked in combined deficiency states 1, 2
Additional Targeted Tests Based on Clinical Context
- Urinalysis or urine microscopy: Exclude hematuria as ongoing blood loss source 1, 2
- Serum creatinine: Assess for chronic kidney disease causing reduced erythropoietin production 1, 2
- Celiac serology (tissue transglutaminase antibody): Found in 3-5% of iron deficiency anemia cases 1, 2
- Haptoglobin and lactate dehydrogenase (LDH): When hemolysis is suspected based on elevated reticulocytes 2
Critical Diagnostic Pitfalls to Avoid
Do not accept normal ferritin at face value in patients with chronic disease, kidney disease, or rheumatoid arthritis. Ferritin >100-500 μg/L can still represent functional iron deficiency if TSAT is <20-30% due to inflammation artificially elevating ferritin 1, 2. In CKD patients specifically, iron deficiency is defined as TSAT ≤30% and ferritin ≤500 ng/mL 1.
Watch for combined deficiency states presenting as normocytic anemia. Simultaneous iron and B12/folate deficiency can mask each other's typical MCV changes, making both deficiencies harder to detect 1, 2. MCH may be more reliable than MCV for detecting iron deficiency in these situations 1.
A good response to iron therapy (hemoglobin rise ≥10 g/L within 2 weeks) is highly suggestive of absolute iron deficiency, even if initial iron studies were equivocal. 1 This therapeutic trial can serve as a diagnostic test when laboratory results are unclear.
Treatment Considerations Based on Laboratory Findings
Iron Deficiency Confirmed
For CKD patients not on dialysis: Trial of IV iron (or alternatively 1-3 month trial of oral iron) when TSAT ≤30% and ferritin ≤500 ng/mL 1
For non-CKD patients: Oral iron is first-line; select route based on severity of deficiency, GI tolerance, absorption capacity, and response to prior therapy 1
Monitoring Response
- Recheck hemoglobin after 1 month of iron therapy: Expect 1-2 g/dL (10-20 g/L) increase if treatment is adequate 1, 3
- If inadequate response: Consider malabsorption, continued bleeding, undiagnosed lesion, or need for parenteral iron 1, 3
- For CKD patients on treatment: Monitor iron status (TSAT and ferritin) at least every 3 months 1