Rapid Determination of Erythrocyte Pyruvate Kinase Activity

We report a new potentiometric method for determining pyruvate kinase (PK). Enzymatic activity is measured by monitoringthe change inpH produced inthe reaction bufferunder InternationalCommittee forStandardization in Haematology (ICSH) standardized assay conditions, and thelactatedehydrogenasereactionisautomatically subtracted ineach measuringcycle.The analysis,per-formed at 37#{176}C,requires a 10-FL sample (isolated eryth-rocytes or whole blood) and is completed in 2.5 mm. The intra-assay CV is <4 % (PK between 3 and 35 U/g Hb); the interassay CV is 4.0 % (PK 15 U/g Hb); results are linearfrom 3 to 30 U/g Hb. A good correlation with the ICSH referencemethod (x)was found:y = 1.01 lx- 0.5; n = 32; r = 0.9939; S = 0.75 (units: U/g Hb). The reference intervals of the PK activity in isolated erythro-cytes (RBC-PK) were estimatedin89 normalsubjects. We foundthatwomen possess a higherRBC-PK thando men (P <0.0001) and thatthebiological variability (CVb) of RBC-PK is 13.5%. Applicationsof the proposed method to the hematological routine are reported. Indexing Terms: potentiometry pH. hemolytic anemia enzyme activity. heritable disorder