Diagnostic value of zinc protoporphyrin in a screening strategy for α-thalassemia

The definitive diagnosis of α-thalassemia involves detection of a deletion of one or more α-globin that encode the α-chains of Hb (hemoglobin). To determine whether DNA analysis is indicated, screening tests such as mean corpuscular volume (MCV) and Hb typing are employed. α-Thalassemia often correlates with normal or low HbA2 values. Zinc protoporphyrin (ZPP) is usually high in ferropenic anemia or lead-poisoning and is normal or slightly raised in ß-thalassemia. Therefore, ZPP is currently used as a marker to discriminate between ferropenic anemia and β-thalassemia. We investigated the diagnostic potential of ZPP < 150 μmol/mol heme in a screening strategy for α-thalassemia. We measured ZPP and performed DNA analysis for detecting the seven most prevalent α-thalassemia deletions, namely, α3.7, SEA, α20.5, α4.2, MED, FIL, and THAI, in the blood samples of 200 patients with MCV < 70 fL and HbA2 ≤ 3.5%. Deletions were detected in 9% subjects in the ZPP ≥ 150 group (n = 175) and 56% subjects in the ZPP < 150 group (n = 29); this difference was statistically significant (chi-square test, P < 0.001). We conclude that ZPP < 150 μmol/mol heme can be used in a new screening strategy for α-thalassemia.