Veterinary Medicine - July 2008 - (Page 374)

PEER-REVIEWED The diagnostic approach to hematuria A common ﬁnding in dogs and cats, hematuria causes a swarm of differential diagnoses to come to mind. This internist provides a series of algorithms to help you zero in on the cause. Mary Bowles, DVM, DACVIM H ematuria can be undetectable on gross examination of urine samples, or the red blood cells (RBCs) can impart a variety of colors to urine and must be distinguished from other components that discolor urine. Hematuria is a common nding in dogs and cats, but identifying the source can be dif cult since RBCs can be introduced anywhere along the urinary tract and may arise from the genital tract as well. Underlying causes of hematuria range from iatrogenic sources such as sample collection technique to disorders that produce marked morbidity. This article and the accompanying algorithms are intended to guide practitioners through the series of steps necessary to con rm the presence of hematuria, localize the source of the RBCs, and identify the speci c cause. as a source of urine discoloration is an important rst step in correctly identifying and pursuing patient problems (Figure 1). Dipstick colorimetric testing is a readily available, economic way to identify blood in urine, but keep in mind that a positive result is not speci c for intact RBCs but is also compatible with hemoglobinuria or myoglobinuria. And regardless of pigment type, grossly discolored urine can make accurate interpretation of dipstick test pads dif cult. tive dipstick test result for blood, rule out hemoglobinuria and myoglobinuria by inspecting the patient’s plasma. Pink plasma supports hemoglobinuria, while clear plasma is compatible with myoglobinuria or RBC lysis in the urine before sediment examination. Myoglobinuria may be con rmed with an ammonium sulfate test at a commercial laboratory. Rule out bilirubinuria If the result for blood on a dipstick is negative and the result for bilirubin is positive, bilirubinuria most likely accounts for the urine discoloration. The greater the quantity of bilirubin present in the urine, the more likely that discoloration will result. The clinical relevance of bilirubinuria is a separate issue and depends on the patient’s urine speci c gravity, species, and sex. Any amount of bilirubin in a cat’s urine is considered abnormal. Urine with 1.020 is generally considered normal for male and female dogs. Male dogs may normally have up to a 1+ bilirubin reading in concentrated urine. Urine with a bilirubin > 1+ and a speci c gravity > 1.020 is a potentially clinically relevant nding, especially in female dogs. Canine urine with a bilirubin > 1+ and a speci c gravity < 1.020 is clinically relevant regardless of sex.3 Estimate the number of RBCs If the dipstick test result is positive for blood, examine the urine sediment to con rm RBCs and to approximate their number. A small number of RBCs is normal depending on the case and the urine collection method. Voided urine samples may normally have 0 to 8 RBCs/ HPF, catheterized samples may normally have 0 to 5 RBCs/HPF, and cystocentesis samples may normally have 0 to 3 RBCs/ HPF.1,2 While these numbers may seem counterintuitive, keep in mind that some cystocentesis and catheterized samples may be more dif cult to obtain than others, and the degree of potential trauma or contamination during collection must be taken into account when excessive RBCs are present in urine samples obtained by any of these methods. Conversely, if RBCs are absent or relatively lacking in a urine sample obtained by cystocentesis or catheterization when compared with a voided sample, suspect a genital or urethral source of hematuria. STEP 1: CONFIRM THE HEMATURIA Depending on the degree of hematuria, urine can range from a relatively normal yellow-to-amber color to abnormal red, orange, or brown shades. Thus, RBCs may be detected incidentally when you evaluate urine as a part of a routine health examination or discovered when you examine urine as part of a work-up in patients with a variety of clinical signs. Distinguishing substances other than RBCs Check for pseudohematuria A negative urine dipstick result for blood with a concurrent negative result for bilirubin from a patient with discolored urine warrants testing a second urine sample in case RBCs are only intermittently present. If the second sample’s dipstick or sediment examination results remain negative for RBCs, consider Mary Bowles, DVM, DACVIM Department of Veterinary Clinical Sciences Center for Veterinary Health Sciences Oklahoma State University Stillwater, OK 74078 Rule out hemoglobinuria and myoglobinuria In the absence of a marked number of RBCs in a urine sample that had a posi- 374 July 2008 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - July 2008

Veterinary Medicine - July 2008 Contents Leading Off Practical Matters Idea Exchange Clarification Dental Corner The Diagnostic Approach to Hematuria Guidelines for Evaluating Hypercalcemic Cats CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - July 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.