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 th e determination of catalytic concentration of serum lactate dehydrogenase i soenzyme 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 m easurements 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 preanatytical hemolysis. A reference group of 37 men had a near In-Gaussia n distribution for the absolute S-LD-1 catalytic concentration. The geometr ic mean was 76 U/I and an S-LD-1 > 128 U/I (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/I (treatment limit) was associated with a suboptima l outcome from the treatment of metastatic TGCT. The maximum allowable anal ytical positive bias was 5 U/I, and the maximum allowable analytical negati ve bias was -32 U/I. The maximum allowable analytical coefficient of variat ion, CVA, was 11 % (approximate to 14 U/I) at a bias = -5 U/I. For S-LD-1 m easurements not corrected for hemolysis, the decision limit was 145 U/I, th e maximum allowable negative bias -19 U/I, and CVA 8 % (approximate to 12 U /I). A routine correction for hemolysis had a large impact on the analytica l quality specifications.