Analytical imprecision of lactate dehydrogenase in primary serum tubes

Previous studies showed high frequency of duplicate errors of lactate dehydrogenase (LDH) measurement in primary lithium-heparin blood tubes. We hence evaluated imprecision of LDH testing and frequency of replicate errors in primary serum samples centrifuged at two different speeds.

Serum samples were collected from 15 healthy subjects and centrifuged at either 1300 g or 2000 g. Serum LDH was then measured on Beckman Coulter AU5800 using the International Federation of Clinical Chemistry-recommended procedure. Complete blood cell count of top layer of serum supernatant was also performed using Advia 2120. Imprecision was calculated as coefficient of variation of 10 replicates of each serum tube, whereas the frequency of replicate errors was compared to the desirable specifications for imprecision.

Mean LDH values were slightly but significantly higher in serum samples centrifuged at 2000 g rather than 1300 g, whereas blood cell counts were similar. The mean imprecision of LDH was more than double in samples centrifuged at 2000 g than in those centrifuged at 1300 g (8% versus 3%). The percentage of replicate measurements exceeding the desirable specifications was more than threefold higher in samples centrifuged at 2000 g than in those centrifuged at 1300 g (30% versus 9%; P < .001).

The lower frequency of replicated errors in LDH measurement observed using serum samples centrifuged according to manufacturer's instruction suggests that assay precision in serum is better if samples are centrifuged at 1300 g rather than 2000 g when the International Federation of Clinical Chemistry-recommended procedure is used.