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Serum Chemistry Tests

Alanine Transferase

Increased ALT indicates hepatic cell damage or necrosis

Alanine transferase (ALT), formerly known as SGPT, is present in large quantities in the cytoplasm of canine and feline hepatocytes. This enzyme enters the blood when liver cells are damaged or destroyed and circulates for a few days.

This enzyme is a sensitive indicator of active liver damage but does not indicate the cause or reversibility of the damage. Increased serum ALT activity indicates recent or ongoing liver cell damage. An increase of at least three times normal indicates significant liver damage within the previous 2 to 5 days.

               

Albumin

Increased albumin suggests dehydration malnutrition malabsorption, enteritis, and glomerulonephritis causeI decreased albumin. Severe dehydration often increases serum albumin levels.

Albumin is a serum protein that affects osmotic pressure, binds calcium, and transports fatty acids and many drugs.

Starvation, parasitism, chronic malabsorptive disease, chronic liver disease, exudative enteritis, and glornerulonephritis decrease serum albumin levels.

Hypoalbuminemia with normal serum globulin levels suggests decreased albumin production, increased loss, or sequestration. If both albumin and globulin levels are low, hemorrhage, exudation, and dilution are likely causes.

                       

Alkaline Phosphatase

Alkaline phosphatase (AP) is found in both liver and bone.Elevated AP activity in the serum indicates increased production by the liver parenchyma, bile ducts, and growing bone or decreased excretion in bile and urine.  Elevated AP activity does not suggest liver or bone necrosis.

Serum AP activity increases after an episode of acute pancreatitis because of secondary cholangitis. It also increases if liver disease causes a disruption of hepatobiliary architecture with local impairment of bile flow.

Cats have less AP than dogs and the kidneys rapidly excrete slight excesses. Any increased AP activity in cats is significant and suggests cholestasis.

Normal values in puppies and kittens are higher than in adults because of active bone growth. Diseases causing bone remodeling in adults cause slight elevations of less than two times normal.

Persistence of AP activity unrelated to continued disease might be due to decreased clearance secondary to diseases such as renal failure, cirrhosis, or the formation of macroenzymes.

                          

Alpha-2 Acid Glycoprotein (AGP)

Increased AGP is a very early indicator of disease

Alpha-2 acid glycoprotein (AGP) is an acute phase protein manufactured in the liver and found in the blood. Detection of elevated levels of AGP indicate's illness or other stressors even though an animal appears clinically normal. AGP indicates disease before antibodies are created by the immune system and before clinical symptoms are apparent. AGP is elevated by inflammation, infectious diseases, surgery, malignant tumors, autoimmune diseases, liver cirrhoses, and with all types of stress in general.

The AGP test is species specific and is available in kit form.  It can be used as a prognostic indicator to detect subclinical disease and changes in homeostasis and to monitor immune system function, chemotherapy, and vaccine efficacy. In monitoring cancer therapy, continued high levels of AGP where the level was initially high suggests that treatment is not working or not appropriate. Levels above 1000 mg/ml of serum indicate a poor prognosis, especially if subsequent measurements show increasing levels.

                   

Alpha Glutathione S-Transferase (GST)

Increased GST indicates early hepatocyte injury

Alpha glutathione S-transferase (GST) is a superior marker of hepatocyte injury from toxicity; ischemia, and other liver injury. It is unique to hepatocytes, found in high concentrations, and is readily released in response to injury. It comprises 5% of the soluble protein of hepatocytes. Its rapid release into and removal from the circulation provides immediate information regarding liver status. It is a valuable tool in research evaluation of liver damage.


Amino Acid Ratio

branched-chain AA decrease with gluconeogenesis

Protein catabolism, gluconeogenesis, and increased insulin activity reduce serum levels of branched-chain amino acids.  Hepatic insufficiency from portosystemic shunts or liver fibrosis (cirrhosis) increases serum levels of aromatic amino acids. The ratio of branched-chain to aromatic amino acids is termed the amino acid (AA) ratio.

aromatic AA  increase with hepatic insufficiency

The AA ratio is decreased with hepatic encephalopathy.  CNS signs occur because increased levels of aromatic amino acids increase production of inhibitory neurotransmitters, while decreased levels of branched-chain amino acids decrease production of stimulatory neurotransmitters.

Normal branched -chain: aromatic AA ratio >3


Ammonia

Increased ammonia indicates hepatic-insufficiency

Increased baseline blood ammonia levels or persistently high blood ammonia levels after oral administration of ammonium chloride (available as a urine acidifier) indicate hepatic insufficiency. This test is helpful in evaluating animals with chronic weight loss, abnormal CNS signs, and a small liver.  Abnormalities correlate with serum bile acid assays.  Congenital and acquired hepatic shunts, bile duct obstruction, cholangiohepatitis, and cirrhosis increase blood ammonia levels.


Amylase

Increased amylase is an indicator of acute pancreatitis

Pancreatic inflammation, necrosis, or pancreatic duct occlusion releases amylase into the blood and peritoneal cavity. This elevates serum amylase levels to two to three times normal. Increased absorption from upper intestinal inflammation and decreased renal excretion mildly elevate serum amylase activity.

When associated with abdominal pain, increased serum amylase activity suggests acute pancreatitis. Macroamylasemia causes increased levels but is not associated with disease.

Since many cats with acute pancreatitis have amylase within the normal range, trypsin-like immunoreactivity (TLI) is a better test.

Anion Gap

Increased anion gap usually means metabolic acidosis

The anion gap can be used to screen for metabolic acidosis when blood pH cannot be measured. It is calculated with the equation:

Anion gap = (Na + K) - (Cl + HC03)

Anion gap increases when unmeasured anions (lactic acid, keto acids) or exogenous substances (salicylates, ethylene glycol) are present.

The most common cause of increased anion gap in dogs and cats is metabolic acidosis from lactic acidosis, renal failure, diabetes mellitus, ketosis, or hypovolemic shock.

If an increased anion gap cannot be explained by these conditions, consider intoxications (ethylene glycol, salicylate, metaldehyde), dehydration, drug therapy (penicillin), alkalosis, and laboratory error.


Aspartate Transferase (AST)

Increased AST activity suggests muscle necrosis or liver necrosis

Aspartate transferase (AST), formerly known as SGOT, is a mitochondriabound enzyme. It is found in several body tissues but is especially high in liver and striated muscle.

Serum AST activity is elevated with skeletal muscle necrosis and hepatocellular necrosis. Elevated serum AST activity with no ALT elevation indicates muscle necrosis. In liver damage, AST activity rises more slowly than ALT and indicates more complete cellular disruption because it leaks from the cell only with necrosis, not membrane instability. Increased serum AST activity suggests muscle necrosis or liver necrosis. In liver disease the serum AST returns to normal more rapidly than ALT.

Rising levels indicate continued severe insult to the hepatocytes. The normal plasma half-life is approximately 12 hours in dogs or 2 hours in cats. Persistence of high but stable serum levels past two to three normal half-lives may be due to continued cellular injury; increased synthesis by normal hepatic tissue, or the formation of macroenzymes. Hemolysis and lipernia can falsely elevate serum AST activity.


Bicarbonate (HC03 C02)

Increased bicarbonate usually means acidosis

Bicarbonate is measured as C02 or HC03 on routine blood panels. Values can increase in respiratory acidosis or metabolic alkalosis, and decrease in metabolic acidosis or respiratory alkalosis.

                        Dogs      Cats

Normal 18-24 mEq/L 18-24 mEq/L

Acidosis < 18 mEq/L < 18 mEq/L


Bile Acid

Increased bile acids screen for congenital macroscopic and microscopic vascular shunts

Increased bile acids with + alkaline phosphatase occur with cholangiohepatitis not steroid induction

Serum bile acid assays are used to evaluate the excretory system of the liver. They are helpful in determining the cause of chronic weight loss, abnormal CNS signs, and a small liver.

Test paired serum samples (fasting and 2 hours after eating) Congenital and acquired hepatic shunts, bile duct obstruction, cholangiohepatitis, and cirrhosis increase serum bile acid levels. Occasionally, the fasting bile acid values are higher than the postprandial values. This is due to stimulation of the gallbladder by stomach juices that pass into the intestine. If either value exceeds the upper postprandial values, shunting is indicated.

In young animals with seizures but no obvious liver disease, bile acids are used to check for congenital macroscopic and microscopic vascular shunts.

In animals with persistently increased ALT or other indications of hepatobiliary disease, abnormally high bile acids indicate shunting because of the increased resistance of hepatic portal blood flow from intrahepatic disease. This is a good indication of active liver disease. Low levels of bile acids with high alkaline phosphatase levels would suggest steroid hepatopathy rather than cholangitis.

                                                   Dogs               Cats

Preprandial (SU)               <10 Ámol/L         <5 Ámol/L

Postprandial (1U)              <25 Ámol/L         <15 Ámol/L

Severe liver dysfunction      >35 Ámol/L        >35 Ámol/L