Effect of temperature, storage time, and sample type on sorbitol dehydrogenase activity in llama serum and plasma

Serum and heparinized plasma samples were collected from 11 adult, clinically healthy llamas. Aliquots were assayed for sorbitol dehydrogenase (SDH) activity after storage at room temperature (20 degrees C), 4 degrees C, or -20 degrees C for defined time intervals up to 1 week postcollection. Sorbitol dehydrogenase activity in all samples was within reference intervals for our laboratory. No difference was found between serum and plasma SDH activity when measured immediately (within 1 hour) after collection. Sorbitol dehydrogenase activity decreased to 79% of initial activity by 24 hours in serum stored at room temperature; plasma had 94% of initial SDH activity under the same conditions. Sorbitol dehydrogenase activity was stable in both plasma and serum stored for up to 1 week at 4 degrees C or -20 degrees C. With the exception of serum stored at 20 degrees C for > 8 hours, in vitro stability of llama SDH was adequate or its use in diagnostic testing.