Increased serum liver enzyme activities may be noted with either primary liver disease or a reactive hepatopathy. Common causes
of increased liver enzyme activities include hepatic neoplasia, pancreatitis, cholangitis from bacteria that presumably originate
from the intestines, hepatic lipidosis, and cholangiohepatitis. Normal enzyme activities do not rule out liver disease. In
cats with cirrhosis, liver enzyme activities may be normal because of decreased functional hepatocellular mass and a subsequent
decrease in liver enzyme production. Alkaline phosphatase (ALP) activity is not usually increased in cats with hepatic tumors,
probably because its serum half-life is short. Gamma-glutamyltransferase (GGT) has greater sensitivity than ALP does for feline
liver disease, except in cases of hepatic lipidosis.6 An increase in ALP without a concurrent increase in GGT is consistent with hepatic lipidosis.
An increased bilirubin concentration may occur with hepatobiliary disease and hemolysis. Hemolysis must cause a rapid and
marked drop in red blood cells to produce clinical icterus. Icterus is usually not detectable in the sclera until the serum
bilirubin concentration is > 3 mg/dl.
If hepatic disease is suspected, measure fasting and postprandial serum bile acid concentrations to confirm liver dysfunction.
If a hepatopathy is suspected, remember that cholangiohepatitis, pancreatitis, and intestinal disease frequently occur together
in cats and are referred to as triaditis. Assessing amylase and lipase activities is not helpful in diagnosing clinical pancreatitis in cats.7
Hypercalcemia may occur with renal disease, paraneoplastic syndrome (e.g. lymphoma, squamous cell carcinoma), idiopathic hypercalcemia, primary hyperparathyroidism, and laboratory error (which is
the most common cause and can occur with lipemic and hemolyzed blood samples). Hypercalcemia of malignancy is rare in cats.8 Cats do not have a linear relationship between serum total calcium and albumin concentrations and the total protein concentration,
so do not adjust the calcium concentration based on the albumin concentration. Evaluating concentrations of ionized calcium,
parathyroid hormone, and parathyroid-related protein (a substance released by cancer cells that mimics the effects of parathyroid
hormone) can help identify the cause of hypercalcemia.
A cat is hypoglycemic if its blood glucose concentration is < 60 mg/dl. The most common causes of hypoglycemia are liver failure,
sepsis, prolonged sample storage, and iatrogenic causes (e.g. insulin therapy). Increases in blood glucose concentration should be interpreted with knowledge of the urine glucose concentration.
Because hyperglycemia may be transient or caused by stress, if there is doubt about the cause of the hyperglycemia obtain
a serum fructosamine concentration to assess the average blood glucose concentration over the preceding two to three weeks.
Serum T4 concentration
Nonthyroidal illness may decrease the serum T4 concentration into the normal range, or even below normal, in a hyperthyroid cat. More severe illnesses tend to be associated
with lower T4 values.9 Additional testing, such as a free T4 by equilibrium dialysis, may be needed if you suspect hyperthyroidism, even with a normal serum T4 concentration.
Performing a urinalysis at the same time as the CBC and serum chemistry profile reveals a wealth of information. You can detect
diabetes mellitus, inadequate urine concentrating ability, ketonuria, proteinuria, hematuria, crystalluria, ongoing renal
tubule damage, and a bacterial urinary tract infection. A suboptimal urine concentration may be present with acute or chronic
renal insufficiency or failure, pyelonephritis, hyperthyroidism, diabetes mellitus or diabetes insipidus, or polydipsia caused
by the reasons mentioned earlier.
Urine protein:creatinine ratio
Protein loss into the urine may cause chronic weight loss. Proteinuria should prompt a thorough evaluation for an underlying
cause. If indicated, request a urine protein:creatinine ratio; normal is < 0.5. Glomerulonephritis can occur secondary to
chronic infectious, inflammatory, and neoplastic conditions. Glomerulosclerosis can occur secondary to diabetes mellitus,
hyperfiltration, and hypertension. Preglomerular proteinuria can occur from increases in the serum protein concentration (>
Urinary tract infections can be occult (without pyuria or hematuria) with diseases or medications, such as glucocorticoids,
that suppress the inflammatory response and immune system. Older cats are also more prone to urinary tract infections because
of immune system senescence and inadequate urine concentrating ability. Urine, obtained by cystocentesis, should be submitted
for bacterial culture and antimicrobial sensitivity testing.