Diagnostic markers for exocrine pancreatic disease

Diagnostic markers for exocrine pancreatic disease

Serum lipase activity remains a sensitive indicator for canine pancreatitis

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Exocrine pancreatic disorders are common in dogs and cats. Based on clinical findings, pancreatitis is the most-common exocrine pancreatic disorder in small animals, followed by exocrine pancreatic insufficiency, exocrine pancreatic neoplasia, and some rare conditions.

The following discussion will focus on diagnostic markers for pancreatitis and exocrine pancreatic insufficiency in dogs and cats.

•Diagnostic markers for pancreatitis The true incidence of pancreatitis in dogs and cats is unknown, but a recent study suggests that, similarly to human beings, pancreatitis in dogs remains undiagnosed in the vast majority of cases. This might be due to subclinical or mild disease in some patients that are not presented to a veterinarian. The low rate of diagnosis also might be due to non-specific clinical signs and diagnostic findings in dogs and cats with pancreatitis.

Thus, in spite of the many advances in the diagnosis of canine and feline pancreatitis, the diagnosis remains challenging in many cases. Many minimally invasive diagnostic tests for canine and feline pancreatitis have been described. However, few have been found to be clinically useful.

•Trypsinogen activation peptide (TAP) When trypsinogen is activated to trypsin, a small peptide, trypsinogen activation peptide (TAP) is cleaved from the trypsinogen molecule. Under normal conditions activation of trypsinogen is limited to the small intestine. Thus, normal dogs and cats have no or only minimal concentrations of TAP circulating in the blood stream. During pancreatitis, trypsinogen is activated prematurely in pancreatic acinar cells, and TAP is released into the vascular space.

Unfortunately, clinical trials have shown that the diagnostic indices for TAP are suboptimal in both dogs and cats. This is most likely due to the short serum half-life of TAP in combination with the fact that veterinary patients with pancreatitis rarely are presented during the first 24-48 hours after disease initiation.

•Serum lipase activity Serum lipase activity has been used to diagnose canine pancreatitis for several decades. However, it has been well recognized that serum lipase activity is neither very sensitive, nor very specific for pancreatitis. This is due to the fact that many different cells in the body synthesize and secrete lipases that all can contribute to the serum lipase activity measured. Serum lipase activity decreases in dogs after pancreatectomy indicating that some of the lipase activity present in the serum does originate from the exocrine pancreas. However, considerable serum lipase activity remains in dogs after pancreatectomy, indicating that lipase activity in serum also originates from other tissues.

Also, many non-pancreatic conditions, such as gastrointestinal, renal, or hepatic disorders or even heat stress or glucocorticoid administration, have been associated with an increase in serum lipase activity. While some dogs with pancreatitis have elevated serum lipase activity, others display no or only mild elevations. Thus, in dogs, serum lipase activity only should be used as a screening test until the diagnosis can be confirmed by other, more-specific, diagnostic modalities.

Also, if serum lipase activity is analyzed, it 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.

Cats with experimentally-induced pancreatitis showed significantly increased serum lipase activities, but cats with spontaneous pancreatitis did not. In one study, not a single cat with pancreatitis had a serum lipase activity outside the reference range. Thus, it appears that, in cats, serum lipase activity is of no clinical usefulness for the diagnosis of pancreatitis.

•Serum amylase activity Like serum lipase activity, serum amylase activity is neither sensitive nor specific for pancreatitis. While some dogs with spontaneous pancreatitis have an elevated serum amylase activity, others have serum amylase activities in the normal range. Furthermore, many dogs with non-pancreatic conditions have elevations of serum amylase activity. As for serum lipase activity, serum amylase activity only should be used as a screening tool for canine pancreatitis until the diagnosis can be confirmed by more-specific diagnostic modalities.

Serum amylase activity has been shown to be decreased in cats with experimentally-induced pancreatitis, but in cats with spontaneous disease serum amylase, activity was of no clinical value.