Elevated Lactate Dehydrogenase Concentrations in Plasma Compared to Serum

To evaluate the difference in lactate dehydrogenase (LDH) concentrations in plasma vs serum specimens in our patient population.

We measured LDH in 110 paired plasma and serum specimens over a 2-week period. Hemolytic indices were performed on each specimen. These paired specimens were drawn in a single setting and stored under the same conditions. For the last 14 paired specimens, cell counts were performed on the plasma/serum.

Plasma LDH was on average 22% higher than serum LDH. There was no difference in the hemolytic indices between the plasma and the serum specimens. In the last 14 specimens, cell counts revealed increased platelets in the plasma specimens compared to the serum specimens.

We propose switching back to using serum for LDH testing because there was unpredictable elevation in plasma LDH concentrations. These elevations in LDH levels may be linked to the platelets present in plasma and that may lyse or become activated with storage at refrigerated temperature.