The effects of storage time and temperature on the stability of salivary phosphatases, transaminases and dehydrogenase.

OBJECTIVES: To investigate the influence of temperature and storage time on salivary acid phosphatase (ACP), tartrate-resistant acid phosphatase (TRAP), alkaline phosphatase (ALP), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and lactate dehydrogenase (LDH).

DESIGN: Unstimulated whole expectorated saliva was collected from healthy men and women subjects (n=26) between 8 and 10a.m. The saliva samples were centrifuged, and the supernatants were measured for ACP, TRAP, ALP, AST, ALT and LDH activities immediately (without freezing) [baseline values] and after time intervals of 3, 7, 14 and 28days (d) of storage at -20°C and -80°C using spectrophotometric methods The influence of storage time was analyzed by one-way ANOVA followed by the Dunnett post-test, while the paired Student's-t-test was used to compare the differences between the temperature (p<0.05).

RESULTS: There was significant decline in the activities of all enzymes at -20°C with increasing storage time. This decrease was relevant from day 14 onward for the majority of the enzymes, with the exception of AST. After day 28, the more sensitive enzymes were ALP and LDH, which showed residual activity of 39% and 16%, respectively, compared with baseline values. There were considerable, but insignificant changes, in the activities of all enzymes after storage at -80°C for 28days.

CONCLUSIONS: Frozen samples should be kept at -80°C to preserve these activities, but there are restrictions for the enzymes ALP, ALT and LDH. Storage of samples at -20°C could introduce high error variance in measured activities.