Transiently elevated apparent lipase by nephelometry.

Occasional patient sera showing normal or minimally elevated lipase activity in the 6-hour titrimetric assay and discordantly high lipase activity in the 6-minute nephelometric assay were encountered. Most of these sera had normal amylase activity. They represented about 1% of outpatient sera subjected to amylase assay. A few sera with discordant lipase activities showed elevated amylase activities and were from patients with the diagnosis of pancreatic dysfunction. Nephelometric lipase assay in these sera showed pronounced nonlinear kinetics; in the most discordant cases a gradual decay of initially high activity to zero occurred. Elevated nephelometric lipase activity was lost inordinately in serial dilution of serum or on serial reduction of undiluted assay volume. In tracer experiments, two of these sera liberated no significant amount of free fatty acids after extensive "de-emulsification" of the nephelometric substrate mixture. This nonlipolytic "deemulsifying" activity was found to be relatively heat-stable in one serum. The nature of this activity remains obscure. A simple and effective protocol is suggested to detect and identify these aberrant nephelometric lipases in the routine laboratory.