Analytical Quality Specifications for Serum Lactate Dehydrogenase Isoenzyme 1 Based on Clinical Goals

The aim of the study was to deduce analytical quality specifications for the determination of catalytic concentration of serum lactate dehydrogenase isoenzyme 1 (S-LD-1) according to clinical goals (the clinical utility model). We defined clinical goals for false positive and false negative S-LD-1 measurements in the monitoring of patients with testicular germ cell tumors (TGCT), clinical stage I, on a surveillance only program. The absolute S-LD-1 catalytic concentrations were routinely corrected for contamination from preanalytical hemolysis. A reference group of 37 men had a near ln-Gaussian distribution for the absolute S-LD-1 catalytic concentration. The geometric mean was 76 U/l and an S-LD-1 > 128 U/l (99.72 percentile, the decision limit) indicated a high risk of a relapse of TGCT. We have previously shown that an S-LD-1 > 160 U/l (treatment limit) was associated with a suboptimal outcome from the treatment of metastatic TGCT. The maximum allowable analytical positive bias was 5 U/l, and the maximum allowable analytical negative bias was −32 U/l. The maximum allowable analytical coefficient of variation, CVA, was 11 % (≈14 U/l) at a bias = −5 U/l. For S-LD-1 measurements not corrected for hemolysis, the decision limit was 145 U/l, the maximum allowable negative bias −19 U/l, and CVA 8 % (≈12 U/l). A routine correction for hemolysis had a large impact on the analytical quality specifications.