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Clinical Pathology


Individual Chemistry Tests

All the chemistry tests that are components of our panels can be ordered individually. There are also some tests that are not included in the panel, which must be ordered as individual tests. These are indicated below. Click on certain tests to obtain more information. Please refer to our Chemistry Module for additional information about the tests, including disease associations.

Bile acids:

Bile acids provide useful information about the portal venous circulation and hepatic function.

Bile acids aid in fat absorption and modulate cholesterol levels. They are produced from cholesterol in the liver and are stored in the gall bladder. Gall bladder contraction with feeding releases bile acids into the intestine. Bile acids undergo enterohepatic circulation, i.e. they are absorbed in the intestine and taken up by hepatocytes for re-excretion into bile. Bile acids increase in circulation under the following conditions:

Cholestasis: bile acids (along with conjugated bilirubin) regurgitate back into blood. Bile acids do not provide any additional information about hepatic function in the presence of cholestasis.
Liver disease: Bile acid extraction from portal blood is impaired, resulting in increased blood levels.
Portosystemic shunts: Congenital and acquired vascular shunts allow an increased proportion of portal blood to bypass the liver.
Measurement of bile acid concentrations is, therefore, a good indicator of hepatobiliary function, but is not specific for the type of underlying disease. In addition, extrahepatic diseases (e.g. metabolic diseases like hyperadrenocorticism) can elevate bile acid concentrations.

In small animals, measurement of both fasting and post-prandial bile acids is useful. Feeding stimulates gall bladder contraction which releases bile acids into the intestine and portal circulation (after intestinal absorption). This increases the load of bile acids that must be extracted from blood by the liver and increases the sensitivity of the procedure to hepatobiliary or vascular defects. Note that horses lack gall bladders and only fasting or random bile acid concentrations are measured in these species. Furthermore, the range of bile acid concentration in healthy ruminants is quite large, decreasing its diagnostic utility.

Bile Acid Interpretation

For more information to bile acids, refer to the specialized chemistry test section.

Cholinesterase:

Measurement of cholinesterase activity in serum or plasma is a quick screening test indicated for animals with a history of possible exposure to organophosphate or carbamate compounds and/or that show clinical signs compatible with exposure. Remember that erythrocytes are rich in cholinesterase, therefore hemolysis invalidates the results.

LDH:

Lactate dehydrogenase catalyzes the conversion of lactate to pyruvate. It is not tissue-specific, being found in a variety of tissues, including liver, heart and skeletal muscle. There are at least 5 different isoenzymes, which are found in varying proportions in different tissues. Because LDH is so non-specific and isoenzyme measurement is not routinely available, its measurement does not confer any additional information about skeletal muscle or hepatic disease in domestic animals, than that provided by enzyme assays routinely used for this purpose (i.e. CK for muscle and SDH and ALT for liver).

Lipase:

Lipase hydrolyzes triglycerides and is used primarily as an indicator of pancreatitis in dogs. Lipase concentrations are variably increased in cats with pancreatitis, so it is less useful in this species.

Non-essential fatty acid (NEFAs), B-hydroxybutyrate (BHB) and metabolic profile testing in cattle:

NEFAs are performed to evaluate the energy balance of prepartum dairy cows, in particular. BHB testing is performed to determine the incidence of sub-clinical ketosis in dairy cows post-calving. These tests should never be interpreted on an individual cow basis and are only meaningful when interpreted on a herd-basis. For this reason, we recommend a minimum of 12 samples be submitted from each herd for this testing (these samples can be submitted whenever suitable cows can be tested and do not have to be submitted simultaneously - they should, however, be interpreted together). We also offer a metabolic profile test in dairy cows post-calving. This test includes BHB, NEFAs, Urea, albumin and AST. We will provide guidelines on interpretation with the test results.

Osmolality:

Serum and urine osmolality is affected by the number of osmotically active particles in solution and is unaffected by their molecular weight and size. For this reason, osmolality is superior to specific gravity, which is affected by particle weight and size.We measure osmolality with a freezing point depression osmometer; 1 osmol (defined as 1 mol of a nondissolving substance in 1 kg H2O) will decrease the freezing point by 1.86°C. Normal serum or plasma osmolality is between 290 and 330 mOsm/kg and is determined principally by sodium, which together with glucose, is an effective osmol. Urine osmolality is useful for evaluating urine concentrating ability, e.g. water deprivation tests, and is more accurate than measurement of urine specific gravity in this regard. Serum or plasma osmolality provides valuable information in suspected hyperosmolar states, e.g. hyperosmolar diabetic ketoacidosis or ethylene glycol poisoning. In the latter condition, an osmolal gap can be calculated from the measured osmolality minus the calculated osmolality. A very high osmolal gap (> 25) supports a diagnosis of ethylene glycol poisoning. Calculated osmolality is determined as follows:

Calculated osmolality = 2 x (Na + K) + (glucose ÷ 18) + (BUN ÷ 2.8),
where values for glucose and BUN are in mg/dL and values for Na and K are in mEq/L

SDH:

Sorbitol dehydrogenase is found in highest concentration in the liver. It is a cytoplasmic enzyme with a short half life (12-24 hours). It is a very specific indicator of liver disease in all species, with increases occurring within 24 hours of liver injury. SDH is the enzyme of choice for detecting hepatocellular injury in large animals and is included in our large animal chemistry panel.

Triglycerides:

Triglycerides are found in high concentrations in chylomicrons (CM) and very low density lipoproteins (VLDL). CM carry lipid absorbed after eating from the GI tract for uptake by adipose tissue and skeletal muscle. VLDL are produced in the liver from free fatty acids and are the main carrier of triglycerides in the fasting state, transporting triglycerides and cholesterol from the liver to peripheral tissues. Increased triglycerides can be seen secondary to increased CM (e.g. post-prandially) or increased VLDL (diseases, such as pancreatitis, diabetes mellitus, Cushing's etc). Visible lactescence (lipemia) in a blood sample is due to increased triglycerides.

Uric acid:

Uric acid is formed in the liver from the catabolism of the nucleic acids, adenine and guanine. Certain dog breeds, e.g. Dalmatians, have a defect in uric acid metabolism, resulting in supersaturation of the urine with uric acid. This predisposes this breed to urate urolithiasis (see uric acid under our urine tests). Uric acid is also used to assess renal function in birds (see non-mammalian chemistry panel). It can be measured in urine or blood.