Value of Erythrocyte ZPP (Zinc Protoporphyrin) and MCV in Differential Diagnosis of b-Thalassemia Minor and Iron Deficiency Anemia (a Study on 1000 Patients)
The purpose of this study was to assess the clinical usefulness of the measurement of erythrocyte zinc protoporphyrin (ZPP) and mean corpuscular volume (MCV), as well as the possible use of other assays, in differential diagnosis of iron deficiency anemia (IDA) and beta-thalassemia minor. This prospective study was conducted on a consecutive series of patients at the hematology clinic of one of the regional referral hospitals of the Tehran University of Medical Sciences (in Tehran, Iran). A total of 1,003 patients were studied between June and August 2000. Complete blood count (CBC) and ZPP assays were performed for all patients, followed by further diagnostic tests as warranted in each case. Such assays included serum iron, serum ferritin, total iron binding capacity (TIBC), hemoglobin A2, and hemoglobin F for the patients within the scope of this study (i.e. iron deficiency anemia and thalassemia). Of the 1,003 subjects studied, 142 (14.2%) had iron deficiency anemia, 88 (8.8%) had beta-thalassemia minor and 48 (4.8%) had evidence of anemia of chronic disease (ACD). 321 (32%) of the patients had elevated ZPP (ZPP > 35), of which 138 (43%) had iron deficiency anemia and 34 (10.6%) had thalassemia. Of the 54 patients who had elevated ZPP together with normal ferritin, 32 (59.3%) had thalassemia and 15 (27.8%) had ACD, while only one patient (1.9%) had IDA. Among the 85 patients who had ZPP in the range of 15 to 35 together with MCV less than 76, we found that 53 (62.4%) had thalassemia while only 2 (2.4%) had IDA. A total of 137 patients had ZPP between 15 and 35, of which 131 had serum ferritin levels between 15 and 400 micrograms/L. Among these 131 patients, 54 (41.2%) had thalassemia, 29 (22.1%) had ACD while only one patient (0.8%) had IDA. ZPP values are increased in over 97% of the patients with iron deficiency anemia (138 of the 142 patients with IDA) and in part of the patients with thalassemia (34 of the 88 cases or 38.6%). The combined measurement of ZPP and MCV can result in correct classification of these patients with significant accuracy. The predictive value of this method is better than the results from the formulae based on RBC indices. In screening programs of the general population for thalassemia, MCV can be used as the initial test followed by ZPP assay as the second test in those patients who have microcytosis. Measurement of ZPP is a simple, quick, and relatively cheap method which can help differentiate between patients with microcytosis due to iron deficiency anemia and with microcytosis due to thalassemia.