Blood work: revelations, limitations for cattle - DVM
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Blood work: revelations, limitations for cattle


DVM360 MAGAZINE


If the TIBC is high or the TIBC is normal and the serum ferritin is low, the anemia is due to iron deficiency. If the TIBC is low, the anemia is from chronic disease. Determining the difference is important because, even if chronic blood loss is stopped, these animals might have trouble regenerating RBCs without parenteral iron supplementation.

Total protein easily can be evaluated with a refractometer, although a chemistry panel is required to determine albumin and globulin changes specifically. The difference in plasma protein and serum protein is mainly due to fibrinogen. Increases in total protein are due to dehydration or inflammation.

Physical examination and/or globulins and fibrinogen are needed to determine the exact cause. Hypoproteinemia most often is caused by lack of adequate protein in the diet or protein loss. Liver disease usually does not result in a low protein in ruminants. Nutrition problems and chronic parasitism should be ruled out first. These animals might be anemic also. If these are ruled out, loss from the gastrointestinal tract, urinary tract or into the peritoneal or pleural cavities should be suspected.

Loss from the gastrointestinal tract is difficult to prove without an intestinal biopsy, so a thorough physical examination is necessary to rule out pleuritis and peritonitis. A urinalysis also should be performed. Results that show proteinuria without evidence of infection point to amyloidosis. If these are ruled out, loss from the gastrointestinal tract can be assumed.

Johne's disease should be next on the differential list. Other inflammatory bowel diseases such as lymphocytic-plasmacytic or eosinophilic enteritis occur but are rare.

Evaluating fibrinogen, globulin

Although there are other acute phase proteins that increase during inflammation, fibrinogen is the one that can be readily assessed in practice. A quick way to estimate fibrinogen is to subtract the serum protein (from clotted blood) from the plasma protein (blood in anticoagulant) that's measured by a refractometer.

Multiply the total by 1,000. An increase in fibrinogen occurs approximately 24 hours after the start of an inflammatory process.

As long as the inflammation is active, the fibrinogen usually will stay elevated.

The exception is when the inflammatory process leads to severe debilitation, and the liver no longer can produce fibrinogen. Globulin levels also will increase with inflammation and remain elevated even after fibrinogen levels returns to normal.

The reason fibrinogen and globulin levels are important to evaluate is because the white blood-cell count usually does not accurately reflect inflammation in cattle. Cattle have a small, marginated pool of neutrophils, so they don't have a ready reserve to start circulating when they are needed, and neutrophilia is not always seen. Since the marginated pool is low, the bone marrow responds by putting immature neutrophils in the blood. A left shift can occur early and dramatically in cattle. A severe left shift indicates severe inflammation, but it is not the death sentence it is for small animals.

Cattle normally have many different sizes of circulating lymphocytes, so large, reactive-looking lymphocytes should not be interpreted as neoplastic cells. Also, a common mistake is to confuse persistent lymphocytosis with lymphosarcoma.

Persistent lymphocytosis (an increase in absolute lymphocyte count at least 3 standard deviations above the normal mean for three months) is an indication of BLV infection only, not the presence of tumors.

Chemistry panel

One of the most useful parts of a serum chemistry profile is the electrolyte values (sodium, potassium, chloride, total CO2). They not only help diagnose certain problems, but they can be useful in making fluid therapy decisions. Most electrolyte abnormalities in adult cattle are a high TCO2 (metabolic alkalosis), hypochloremia and hypokalemia, particularly in cattle with gastrointestinal disease.

Hypokalemia is common in anorexic animals but should be interpreted with the acid-base status. Acidosis might cause hyperkalemia, but total body potassium is rarely elevated and is usually low. Potassium can be supplemented in the face of hyperkalemia if the acidosis is corrected at the same time. Make sure that serum has not been sitting on the clot too long and that hemolysis does not occur; both of these conditions will falsely increase potassium.

Hyponatremia and hypochloremia can occur with diarrhea.


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Source: DVM360 MAGAZINE,
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