Fecal alpha1-protease inhibitor measurement
Fecal alpha1-protease inhibitor is a protein that can be measured in feces to detect excess protein loss through the GI tract.* In a study
of nine cats with chronic GI disease, eight had increased fecal alpha1-protease inhibitor concentrations.17 The sample should be collected through defecation, not digitally. In a study performed in dogs, most digitally collected
samples had increased alpha1-protease inhibitor concentrations compared with samples spontaneously voided, probably because of trauma to the rectal mucosa
and resultant leakage of the protein.18
Ultrasonography is commonly performed in patients with weight loss. Evaluate the patient for normal echogenicity of organs
relative to each other (e.g. the spleen should be more echogenic than the liver, which should be greater or equal in echogenicity to the renal cortices);
masses; bladder, kidney, or gallbladder stones; lymph node enlargement; cystic structures; increased organ size or thickness
of GI wall layers; apparent discomfort with transducer pressure; and regional or generalized free abdominal fluid.
I recommend attempting to image the pancreas in every patient undergoing abdominal ultrasonography, regardless of the presenting
problem, to learn to identify the pancreas and recognize the variability in the normal pancreas. A width of greater than 1
cm in a ventrodorsal dimension for the left limb of the pancreas is suspicious for pancreatic enlargement in cats. In a study
of 84 cats, the obtained 95% reference interval for this dimension was 2.6 to 9.5 mm,19 and the size and echogenicity of the pancreas did not change with age.19 The diagnostic accuracy of ultrasonography in diagnosing feline pancreatitis is variable. Normal ultrasonographic findings
do not rule out pancreatitis in cats because the disease may only be identifiable microscopically and may be focal to multifocal.
Neoplastic infiltration, such as occurs with lymphoma, is also a differential diagnosis for ultrasonographic pancreatic abnormalities.
Increased intestinal wall thickness (> 3 mm in cats) or decreased distinction of the wall layers can be seen with infiltrative
disease, such as inflammatory bowel disease or lymphoma. However, ultrasonography is not sensitive for diagnosing diffuse
infiltrative disease, so a normal ultrasonogram doesn't rule out infiltrative GI disease. It is my impression that palpation
is more sensitive for diagnosing increased intestinal wall thickness than is ultrasonography, especially if the patient is
Cytologic and histologic examination
Collecting fluid or cellular material by fine-needle aspiration or collecting tissue by needle or surgical biopsy for cytologic
or histologic examination may be required to obtain a definitive diagnosis in a cat with weight loss. Fine-needle aspiration
usually poses little risk, and cytologic analysis of obtained samples can diagnose lymphoma, mast cell tumors, some carcinomas,
infections, and hepatic lipidosis. Assess the patient's coagulation status, especially before performing a liver biopsy, and
carefully consider the limitations, risks, and benefits of obtaining samples from various organs. Aspirate free abdominal
fluid as close as possible to the suspected primary lesion for the best chance of obtaining a diagnostic sample. For example,
if liver disease is suspected and fluid is seen both between the liver lobes and near the urinary bladder, the aspirate should
be taken near the liver.
In cases of suspected bacterial cholangitis and cholangiohepatitis, ultrasound-guided transhepatic cholecystocentesis can
be done to obtain bile for cytology and aerobic and anaerobic cultures. Deflating the gallbladder by removing most of the
bile during aspiration reduces the risk of leakage. The procedure is not recommended when necrotizing cholecystitis or extrahepatic
biliary obstruction with a severely distended gallbladder is suspected. A gallbladder wall thickness of greater than 1 mm
is an indication of gallbladder disease, but an ultrasonographically normal gallbladder does not rule out disease.
Pancreatic neoplasia, pancreatitis, and focal septic peritonitis cannot be differentiated ultrasonographically. To make a
definitive diagnosis, perform a cytologic examination of a fine-needle aspirate. Fine-needle aspiration can also diagnose
pancreatic pseudocysts. Since obtaining biopsy samples of the pancreas rarely causes pancreatitis, fine-needle sampling is
considered a low-risk procedure.