Background: The primary responsibility of a blood transfusion service (BTS) is to provide arnsafe, sufficient and timely supply of blood and blood products so as to ensure that blood donationrncauses no harm to the donor. The Copper Sulphate (CuSO4) screening test has been found tornerroneously include anemic people and exclude eligible people and its performance is not wellrnstudied in poor settings like Ethiopia.rnObjectives: To determine the rate of false deferral and false pass of prospective blood donorsrnscreened by the copper sulphate gravimetric test from April to June 2016 at Hossana bloodrnbank, Ethiopia..rnMethods: A cross- sectional study was carried out from April to June 2016 in Hossana bloodrnbank. Blood sample from 422 voluntary donors were collected and analyzed by CuSo4rngravimetric test and automated hematology analyzer (Cell-dyn 1800). The data was entered inrnEpi-Data 3.1 and analyzed by SPSS 20 and interpreted accordingly. P value less than 0.05 wasrnconsidered as statistically significant. Agreement between the two methods was determinedrnusing the Kappa coefficient.rnResult: The overall deferra1 rate was 20.1% by the reference method and varies by bloodrncollection site for the copper sulphate method (15.4% and 16.8% using capillary and wholernblood, respectively). False pass rates were 9.2% and 7.6% and false fail rates were 4.5% andrn4.3% using capillary and venous blood samples, respectively. The CuSo4 method using capillaryrnblood sample had sensitivity of 94.4%, specificity 54.1%, PPV 89.1% and NPV 70.8%, whilernusing venous blood sample it gave sensitivity of 94.7%, specificity 62.4%, PPV 90.9% and NPVrn74.6%. The CuSo4 method had moderate with Kappa value of 0.53, (95% CI, 0.425-0.625,rnP