Evaluation of hemoglobin of blood donors deferred by the copper sulphate method for hemoglobin estimation

Abstract 

Introduction

The copper sulphate (CuSO₄) specific gravity test for Hb screening tends to give inappropriate failures. This prompted us to compare it with alternate screening methods.

Aim

To study the impact of inaccuracy of CuSO₄ method on donor deferral.

Methods

Capillary and venous blood samples of 400 potential blood donors failing the primary Hb screening using appropriately standardized CuSO₄ test (specific gravity 1.053) were tested by Hemocue photometer, the Hb colour scale, Cyanmethemoglobin method as well as the automated hematology analyser, which was considered as the standard reference method.

Results

One hundred and sixteen donors (29%) who failed the CuSO₄ test had true Hb levels >12.5g/dl. The Hb levels of 131 (32.8%) deferred donors were between 12 and 12.5g/dl. The sensitivity of Hemocue, Hb colour scale and Cyanmethemoglobin was 99%, 97% and 96% and their specificity was 45%, 93% and 46%, respectively. The positive predictive values (PPV) of Hemocue and Cyanmethemoglobin methods were low (43% and 44%, respectively) but their negative predictive values (NPV) were high (99%, and 97%, respectively). The Hb colour scale had an overall best performance with a PPV of 96% and NPV of 95%.

Conclusion

The Hemoglobin colour scale which is inexpensive, convenient for field testing and has the overall best performance, is the most suitable for donor Hb screening. Since its readability is 12g/dl, lowering the donor Hb threshold to 12g/dl should be actively considered.

Keywords: Blood donor, Hemoglobin, Deferral, Copper sulphate method