Study of Two in Vitro Diagnostic Tests for Paroxysmal Nocturnal Haemoglobinuria

Summary. The variability with time of the serum haemolytic activity of normal subjects in the acidified‐serum and sucrose‐haemolysis tests towards the red cells of paroxysmal nocturnal haemoglobinuria (PNH) and PNH‐like cells (i.e. normal red cells treated in vitro with the sulfhydryl compound AET) was investigated. A wide variability was observed in samples of serum obtained from individual donors at intervals of months, days, and even hours, without evidence of a circadian rhythm. In spite of this variability each donor of serum, considered in respect to other donors, maintained unchanged with time his rank of serum haemolytic activity towards both PNH and AET cells in the acidified‐serum test, but not in the sucrosehaemolysis test. From the practical point of view it seems convenient for the laboratory diagnosis of PNH to carry out acidified‐serum tests with the serum of one selected normal subject (in addition to the patient's own serum) and sucrosehaemolysis tests with a few random normal sera.