Determination of optimal storage temperature and duration for analysis of total and isoenzyme lactate dehydrogenase activities in canine serum and cerebrospinal fluid.

Abstract

Lactate dehydrogenase (LDH) exists as 5 isoenzymes in both serum and cerebrospinal fluid (CSF). Human studies have demonstrated that changes in LDH activity can be correlated with a particular disease. Conflicting reports regarding the stability of LDH made it necessary to determine storage conditions before further study of the diagnostic power of this enzyme's activity can be pursued in dogs. The purpose of this study was to optimize measurement of LDH activity and analysis of its isoenzyme profile in canine serum and CSF through proper storage. Serum and CSF were collected from 5 healthy dogs. Samples were stored at 22°C, 4°C, or -20°C for up to 2months. Total LDH activity was measured spectrophotometrically. Isoenzyme profiles were determined using the QuickGel LDH Isoenzyme technique and densitometric scanning. Retention of >70% LDH activity in stored samples was considered clinically acceptable. Serum and CSF stored at -20°C retained >85% of the total LDH activity for 4weeks, although CSF total LDH activity degraded by >10% within 24hours of storage. All serum LDH isoenzymes retained >85% activity for up to 4weeks at -20°C. CSF LDH isoenzyme activity degraded rapidly, therefore CSF LDH should be evaluated within 72hours to assure >75% of LDH isoenzyme activity. Proper storage at -20°C can optimize detection of total LDH activity and the LDH isoenzyme profile in canine serum and CSF. This information is important for evaluating the potential usefulness of LDH in veterinary medicine.