Laboratory evaluation of kidney disease - Veterinary Medicine
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Laboratory evaluation of kidney disease
The results of routine blood and urine evaluation can reveal early indicators of renal disease. Know what to be on the lookout for to help you intervene before life-threatening damage occurs.


VETERINARY MEDICINE


OTHER TESTS OF GFR

The ideal substance for measuring GFR should be a) exclusively cleared by glomerular filtration, b) neither secreted nor reabsorbed by the kidney tubules, and c) easily measured.32 Unfortunately, a substance meeting all these criteria is not available as a simple or routine test on most commercially available veterinary biochemical profiles. The crudest estimates of GFR on a serum chemistry profile are BUN and creatinine concentrations; however, as discussed above, measuring and interpreting these values have their limitations.

Cystatin C has been investigated as a marker of GFR in dogs. This cysteine protease inhibitor is freely filtered by the glomerulus and unaffected by nonrenal factors such as inflammation and sex. It correlates well with GFR measurements and may be a reasonable alternative to creatinine concentration measurement.33 The main limitation of cystatin C measurement in people is intraindividual variation. It has lower sensitivity than serum creatinine concentration in detecting changes in the same individual, even though cystatin C may be a better indicator of early decreases in GFR.34 Cystatin C measurement is not available for veterinary patients outside a research setting.

Multiple tests are typically reserved for a laboratory or university setting that provides accurate measurements of GFR. Many of these methods have several disadvantages, including high cost, labor intensiveness, risks caused by anesthesia, or need for specialized equipment or licensing. The gold standard is the urinary clearance of inulin. Other tests include nuclear scintigraphy, clearance tests of endogenous and exogenous creatinine, clearance of chromium-51 EDTA, and the iohexol clearance test.35 Of the aforementioned tests, the iohexol clearance test is probably the most practical and easiest to perform (see the Related Link "Case study: Acute kidney failure from hypotension in a dog" below). It does not require any specialized equipment or urine collection and can be completed in four hours.36,37 (Iohexol measurement for the iohexol clearance test is available at the Diagnostic Center for Population and Animal Health, Michigan State University, 4125 Beaumont Road, Lansing, MI 48910-8104; phone: (517) 353-1683; FAX: (517) 353-5096; http://www.animalhealth.msu.edu/.)

SUMMARY

A combination of routine blood and urine tests, along with more specialized laboratory tests, can provide a wealth of information about the presence of kidney disease and clues about its cause. In addition, these tests may help detect complications associated with kidney disease.

Michael Geist, DVM, DACVIM
VCA Animal Specialty Group
5610 Kearny Mesa Road, Suite B
San Diego, CA 92111

Cathy Langston, DVM, DACVIM
The Animal Medical Center
510 East 62nd St.
New York, NY 10065


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Source: VETERINARY MEDICINE,
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