In addition, many nonpancreatic conditions are associated with a marked increase in serum lipase activity, leading to an incorrect diagnosis of pancreatitis. For example, patients with conditions such as renal failure, glomerulosclerosis, glomerulonephritis, hepatic necrosis, hepatic fatty degeneration, hepatocellular carcinoma, bile duct carcinoma, lymphosarcoma, hemangiosarcoma of the heart, adenocarcinoma of the small intestine, sepsis, and amyloidosis of multiple organs have all been described as having an increased serum lipase activity.^17,20 Also, heat stress and prednisone or dexamethasone administration can cause increased serum lipase activity in dogs.^21-23 While some dogs with pancreatitis have elevated serum lipase activity, others have no or only mild elevations of serum lipase activity.¹⁷

Thus, serum lipase activity is neither sensitive nor specific for diagnosing pancreatitis in dogs and should only be used if an in-house assay with immediate turn-around is available and the results can be confirmed by another, more specific diagnostic modality. Finally, if serum lipase activity is analyzed, I think the results should be interpreted cautiously, and only elevations of three to five times the upper limit of the reference range should be considered suggestive of pancreatitis.

Six cats with experimentally induced pancreatitis had significantly increased serum lipase activities, but 12 cats with spontaneous pancreatitis did not.^24,25 In one study, not a single cat with spontaneous pancreatitis had a serum lipase activity above the upper limit of the reference range.²⁴ These data suggest that serum lipase activity is of no clinical usefulness in diagnosing pancreatitis in cats.²⁴

The diagnostic utility of serum amylase activity for canine and feline pancreatitis is similar to that of serum lipase activity. Dogs with experimentally induced pancreatitis had elevated serum amylase activities.^15,16 Also, some dogs with spontaneous pancreatitis have an elevated serum amylase activity, but others have normal serum amylase activities.¹⁷ Furthermore, dogs with nonpancreatic conditions can have elevated serum amylase activities.^17,20 In contrast to its effect on serum lipase activity, prednisone or dexamethasone administration in clinically healthy dogs led to a decrease in serum amylase activity.^22,23 These data suggest that, as for serum lipase activity, serum amylase activity should only be used to diagnose pancreatitis in dogs if an in-house assay is available and results are available before more specific diagnostic test results can be obtained. Also, the diagnosis must then be confirmed by more accurate diagnostic modalities.

In contrast to serum amylase activity in dogs, serum amylase activity has been shown to be unchanged or decreased in cats with experimental pancreatitis.²⁵ In another study, serum amylase activity was not significantly different among cats with spontaneous pancreatitis, clinically healthy cats, and cats with nonpancreatic diseases.²⁴ These findings suggest that serum amylase activity has no clinical usefulness in diagnosing pancreatitis in cats.

Serum trypsin-like immunoreactivity

The serum trypsin-like immunoreactivity (TLI) assay mainly measures trypsinogen in serum but also detects trypsin and some trypsin molecules bound to proteinase inhibitors. The TLI assay is species-specific, and different assays for people, dogs, and cats have been developed and validated. In healthy patients, a small amount of trypsinogen is secreted into the vascular space, but little or no trypsin is present in serum. Serum TLI originates from the exocrine pancreas almost exclusively.^18,19 Similar studies are not available in cats, but as in dogs, no evidence is available that suggests that serum TLI originates from cells other than pancreatic acinar cells.

Dogs and cats with experimental pancreatitis and some dogs and cats with spontaneous pancreatitis have increased serum TLI concentrations. ^26,27 However, only 30% to 60% of dogs and cats with spontaneous pancreatitis have elevated serum TLI concentrations. This is most likely due to the short half-life of serum TLI concentration.

Trypsinogen activation peptide

When trypsinogen is activated to trypsin, a small peptide, trypsinogen activation peptide (TAP), is split from the trypsinogen molecule. Under normal conditions, trypsinogen activation occurs exclusively in the small intestine. Thus, normal dogs and cats have no or only minimal concentrations of TAP circulating in the bloodstream.²⁸ In patients with pancreatitis, trypsinogen is activated prematurely in pancreatic acinar cells, and TAP is released into the vascular space.