WVC 2017: Don't Underestimate the Importance of Clinical Pathology

Interpreting hemograms and urinalyses as part of a diagnostic workup was the focus of a group of sessions this week at a clinical pathology symposium at the Western Veterinary Conference in Las Vegas, Nevada.

Dr. Dennis DeNicola, DVM, PhD, DACVP, medical affairs fellow with Idexx Laboratories, and Fred Metzger, DVM, MRCVS, DABVP, owner of Metzger Animal Hospital in State College, Pennsylvania, used an interactive, case-based discussion to highlight the importance of proper interpretation of urinalysis and complete blood count (CBC) results when evaluating patients.

The case discussion focused on the diagnostic workup for a cat suspected of having renal disease and concurrent hyperthyroidism. The lecturers noted that the cat’s creatinine level and baseline thyroid level were not elevated significantly, but other indicators suggested underlying illnesses.

Both speakers discussed the importance of symmetric dimethylarginine (SDMA) as an early indicator of renal disease because SDMA increases earlier than serum creatinine does, and elevations are not affected by changes in lean body mass. These factors increase the likelihood of identifying early renal disease before creatinine and other indicators are likely to suggest abnormalities.

The cat in the case presentation was experiencing progressive loss of muscle mass, polydipsia, appetite loss, weight loss, lethargy, and other signs pointing potentially to renal and/or thyroid disease. As part of the patient’s evaluation, the speakers described abnormalities in the CBC such as erythrocyte acanthocytosis, microcytosis, the presence of schistocytes, and other erythrocyte morphologic changes that can occur with renal disease. The speakers stressed that the importance of the hemogram shouldn’t be minimized when evaluating suspect patients.

Radiography also played a prominent role in the diagnostic assessment for the cat in the case discussion. At one point, the cat presented with constipation. Radiographs taken at that time showed renoliths in both kidneys. The speakers noted that this important finding would have gone undetected if the radiographs hadn’t been taken to assess the constipation.

Dr. Metzger cautioned clinicians to include renal imaging and other diagnostics when facing a pet that seems to have chronic kidney disease. He commented, “There are other things that can cause kidney disease. You could have pyelonephritis, renoliths, infectious disease, and other things that can cause renal failure.”

The speakers also cautioned that when evaluating a urine sample, it’s important to consider the urinalysis within the context of other findings. For example, urine specific gravity should be interpreted in the context of the total patient. A urinalysis that reveals trace proteinuria in a normally concentrated urine sample might be insignificant. But trace proteinuria in a very dilute urine sample suggests a much higher amount of protein and could indicate significant pathology.

The speakers recommend that the chemistry panel and other diagnostic findings should be included when assessing the significance of these urinalysis results.