Veterinary Medicine - September 2007 - (Page 594)

Hyperlipidemia O P E E R - R E V I E W E D hypertriglyceridemia. Lipemia becomes grossly detectable at triglyceride concentrations greater than 300 to 400 mg/dl (normal triglyceride concentration = 50 to 150 mg/dl in dogs and 50 to 100 mg/dl in cats) and is a result of the high concentration of large lipoproteins (chylomicrons and VLDLs).1 Elevated concentrations of cholesterol, without increases in chylomicrons or VLDLs, result in increases of LDLs and HDLs and do not affect the gross appearance of the serum or plasma.1 TABLE 4 Effect of Lipemia on Serum Chemistry Parameters in Dogs and Cats* Parameter Total bilirubin Conjugated bilirubin Phosphorus Alkaline phosphatase** Glucose** Total protein Lipase Alanine aminotransferase Creatinine Total CO2 Cholesterol Blood urea nitrogen Canine Serum Increased Increased Increased Increased Increased Increased Increased Increased Decreased Decreased Decreased Decreased Feline Serum Increased Increased Increased Increased Increased Increased NA Decreased Decreased Decreased NA NA Chylomicron test A patient that presents with fasting lipemia can have elevations of chylomicrons, VLDLs, or both. To further evaluate such patients, a chylomicron test can be performed on lactescent serum by allowing the serum or plasma sample to sit undisturbed in a refrigerator for 12 to 14 hours.2 Chylomicrons are less dense than VLDLs and will float to the top of a chilled sample.2 The VLDLs are denser and tend to stay suspended within the serum or plasma. The formation of a creamy layer indicates the presence of chylomicrons. The absence of a creamy layer in a lipemic sample confirms increased VLDLs when the infranatant is cloudy. Formation of a *Source: Nelson RW, Elliot DA. Disorders of metabolism. In: Nelson RW, Couto CG, eds. Small animal internal medicine. 3rd ed. St. Louis, Mo: Mosby, 2003;822-827. **Interference occurs with severe hypertriglyceridemia. When measured using a refractometer. ESSENTIAL ELEMENT The tests Diagnostic tests include evaluating the gross appearance of serum or plasma, a chylomicron test, and measuring triglyceride and cholesterol concentrations in samples from fasting patients; tests to rule out underlying diseases (e.g. lowdose dexamethasone suppression test, serum T4 and thyroidstimulating hormone concentrations, serum pancreatic lipase immunoreactivity); and measuring lipoprotein lipase activity. creamy top-layer and cloudy plasma is indicative of excessive chylomicrons and VLDLs.2 The presence of chylomicrons alone can result from either familial or acquired diseases that result in reduced or absent lipoprotein lipase activity.2 However, the presence of VLDLs suggests that the hyperlipidemia is secondary to decreased or absent lipoprotein lipase activity or increased VLDL production.2 Both chylomicrons and VLDLs may be present in poorly regulated diabetic dogs.2 Triglyceride and cholesterol concentrations Gross lipemia may not be evident in some patients with clinical signs compatible with hyperlipidemia. In these patients, determining fasting serum or plasma triglyceride and cholesterol concentrations is recommended. Total cholesterol is included on many serum chemistry profiles. A triglyceride concentration must be requested as an additional test. When assessing a patient for hyperlipidemia, submit refrigerated or frozen serum rather than plasma or whole blood.2 Lipemia can alter serum biochemical analysis. Chylomicronemia can interfere with other analytes determined by colorimetric methods (Table 4).2,3 Hyperlipidemia can also lead to in vitro hemolysis resulting from altered erythrocyte membrane fragility.2,12 Because of this interference, some laboratories clear lipemic samples by removing chylomicrons. If the laboratories do not report this, false negative results are possible. Therefore, submit paired lipemic samples to the laboratory—one for determining the triglyceride concentration and one to be cleared of chylomicrons and used to perform routine biochemical testing. Reference ranges for serum lipids vary widely depending on the specific laboratory methodology. 1 So use species-specific reference ranges provided by the laboratory whenever possible. The guidelines used in our laboratory to assess the severity of Continued on page 595. 594 September 2007 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - September 2007

Contents Letters Leading Off The Veterinary Medicine Interview: Dr. William J. Kay Idea Exchange Practical Matters Salivary Mucoceles in Cates: A Retropspective Study of Seven Cases Hyperlipidemia in Dogs and Cats Purina Insert The Latest Management Recommendations for Cats and Dogs with Nonketotic Diabetes Mellitus CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - September 2007

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