Effects of hemoglobin F levels, KCN, and storage on the isopropanol precipitation test for unstable hemoglobins.

Although the isopropanol precipitation test is a commonly used and sensitive test for detecting unstable hemoglobins, false-positive reactions are frequently observed. In this study, the storage temperature of the test samples, type of stored sample amount of fetal hemoglobin (Hb F) in the sample, and presence of potassium cyanide (KCN) in the hemolysate preparation all affected the accuracy of the test. The addition of 2% KCN to samples before testing eliminated or greatly reduced false-positive reactions. Hb F levels greater than 4% caused false-positive results. When specimens with Hb F levels less than 4% were stored at 4C and as whole blood, they showed no false-positive reaction for as long as two weeks. However, duplicate specimens stored as whole blood but unrefrigerated and those stored as hemolysates showed false-positive reactions after three days.