A 28-year-old primigravida at 32 weeks of gestation is screened for anemia. Her hemoglobin is 9.5 g/dL. Which laboratory finding best distinguishes iron deficiency anemia from anemia of chronic disease in pregnancy?

Explanation

## Distinguishing Iron Deficiency Anemia from Anemia of Chronic Disease in Pregnancy ### Core Discriminator **Key Point:** Serum ferritin is the **single best laboratory test** to distinguish iron deficiency anemia (IDA) from anemia of chronic disease (ACD). A serum ferritin <30 ng/mL is highly specific for depleted iron stores and is diagnostic of IDA. **High-Yield:** In IDA, ferritin is low (<30 ng/mL) because ferritin directly reflects iron stores. In ACD, ferritin is normal or elevated (>100 ng/mL) because ferritin is an acute-phase reactant that rises with chronic inflammation — even when functional iron availability is reduced. ### Comparison Table | Parameter | Iron Deficiency Anemia | Anemia of Chronic Disease | |---|---|---| | **Serum ferritin** | ↓ (<30 ng/mL) — **best discriminator** | ↑ or normal (>100 ng/mL) | | **TIBC** | ↑ (>360 μg/dL) | ↓ or normal (<300 μg/dL) | | **Serum iron** | ↓ (<60 μg/dL) | ↓ (<60 μg/dL) — *not discriminating* | | **MCV** | ↓ (<80 fL) | Normal or mildly ↓ — *not discriminating* | | **Transferrin saturation** | ↓ (<16%) | ↓ (<16%) — *not discriminating* | ### Why Ferritin is Superior to TIBC 1. **Ferritin directly reflects iron stores:** A low ferritin is virtually pathognomonic of IDA; no other condition lowers ferritin. 2. **TIBC is elevated in IDA** (body upregulates transferrin to maximize absorption) and **low in ACD** (hepcidin suppresses transferrin production) — this is a valid finding, but ferritin is more sensitive and specific as a single discriminator per standard references (Harrison's, WHO guidelines). 3. **Serum iron and MCV** are reduced in BOTH conditions and therefore cannot reliably distinguish between them. 4. **Pregnancy caveat:** Ferritin may be mildly elevated in concurrent infection/inflammation, but a value <30 ng/mL still reliably identifies IDA. Values <12 ng/mL are unequivocally diagnostic. **Clinical Pearl:** According to Harrison's Principles of Internal Medicine and WHO antenatal guidelines, serum ferritin is the recommended first-line test to confirm iron deficiency. TIBC adds confirmatory value but is not the primary discriminator. In resource-limited settings (including routine Indian antenatal care), ferritin is the preferred and most cost-effective single test. **Mnemonic:** **Ferritin = Iron Store Meter** — Low ferritin = empty stores = IDA; High/Normal ferritin = stores intact = ACD (iron trapped, not depleted). *Reference: Harrison's Principles of Internal Medicine, 21st ed., Chapter on Anemias; WHO Guidelines for Antenatal Care.*