Evaluation of the validity of the pre-marriage mean corpuscular volume value as a predictive test for b-thalassemia carrier status

Background: The national mandatory premarital screening test is based on mean corpuscular volume (MCV) > 80 fL value for the detection of b-thalassemia to provide acceptance for marriage. The objective of this study is to assess the efficacy of MCV as a screening test for b-thalassemia trait in the present population. Methods: This study was conducted on 418 blood samples collected from adult individuals. The diagnosis of b-thalassemia carrier was given to those having HbA2 values equal to or above 3.5%. The diagnostic reliability of different RBC indices and formulas in discriminating cases of b-thalassemia trait were evaluated. Finally, a new index called "Momani" was determined based on MCV, RDW and RBC count. Results: b-thalassemia trait was identified in 10% of the cases. The measured MCV value was significantly lower in b-thalassemia carrier group compared to non-carrier group (p = <0.001). MCV value and RBC count showed a higher diagnostic reliability than other RBC indices. We found that MCV ≤ 74.45 fL is more suitable cutoff value of MCV with 86.2% specificity, 71.4% sensitivity, 36.6% positive predictive value, and 96.4% negative predictive value. Finally, our index "Momani" was found to be useful in predicting carrier and paralleled the performance of Sirdah, Mentzer, and Ehsani indices. Conclusions: MCV<80 is a useful but not a perfect cutoff point for the screening of b-thalassemia carriers from noncarriers. The diagnostic accuracy of MCV can be improved by selecting a new cutoff value. Moreover, "Momani" index shows good discrimination ability in diagnosing b-thalassemia carrier in our population