CVC Highlight: Why you should worry about your patients with proteinuria - Veterinary Medicine
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CVC Highlight: Why you should worry about your patients with proteinuria
Don't be quick to dismiss that positive protein result on a urine dipstick test because of a high urine specific gravity or hematuria. Identifying the source of proteinuria early may give you a chance to improve your patient's survival.


VETERINARY MEDICINE



Gregory F. Grauer, DVM, MS, DACVIM
Practitioners have long interpreted proteinuria clinically in conjunction with their canine and feline patients' urine specific gravity and sediment examination results. For example, a urine dipstick colorimetric or sulfosalicylic acid turbidimetric test reading of trace or 1+ protein in urine that has a high specific gravity is often attributed to urine concentration rather than to pathologic proteinuria. Or a dipstick result positive for protein in a patient with microscopic hematuria or pyuria is usually attributed to urinary tract hemorrhage or inflammation.

However, in both cases, these interpretations may be incorrect because these semi-quantitative screening tests have several limitations.1,2

CAN I RELY ON URINE DIPSTICK PROTEIN RESULTS?


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Albumin is the primary protein found in urine in both healthy dogs and cats as well as in dogs and cats with renal disease. The urine dipstick test is the most commonly used screening test, but it has relatively low sensitivity (many false negative results) and low specificity (many false positive results) for albuminuria.1 Although the sulfosalicylic acid test has greater sensitivity than the dipstick test, its specificity for albuminuria is also relatively poor.1 In addition, grading the turbidity of the sulfosalicylic acid test and the dipstick color change is subjective, and results can differ among laboratories and individuals.

Two questions need to be answered when proteinuria/albuminuria is detected on screening tests. One: Is the proteinuria persistent (vs. transient)? Two: What is the cause or origin of the proteinuria? Serial testing along with urine sediment examination will help answer these two questions.

HOW IS PERSISTENT PROTEINURIA DEFINED?

Persistent proteinuria is proteinuria found on three separate screening tests separated by seven to 10 days.2

WHAT ARE THE POSSIBLE CAUSES OF PROTEINURIA?

Proteinuria can be caused by physiologic or pathologic conditions.

Physiologic proteinuria may result from fever, exposure to extreme cold or heat, strenuous exercise, stress, or seizures; it is usually transient and resolves after the underlying cause is corrected.

Pathologic proteinuria can be caused by nonurinary system problems that are prerenal (e.g. Bence-Jones proteins produced by neoplastic plasma cells) or postrenal (e.g. prostatitis or metritis) in origin. To reduce the possibility of contaminating the urine with protein from the lower urinary tract, obtain samples by cystocentesis.

Pathologic proteinuria can also result from urinary system problems and may be nonrenal (lower urinary tract inflammation or hemorrhage) or renal (glomerular or tubulointerstitial conditions) in origin. Renal proteinuria from glomerular and tubular disease is usually persistent and most often accompanied by inactive urine sediment findings, with the exception of hyaline casts. However, renal proteinuria can also result from inflammatory (e.g. pyelonephritis) or infiltrative (e.g. neoplasia) kidney disorders; thus, the urine sediment findings are often active (e.g. bacteriuria, pyuria, hematuria, neoplastic cells). Persistent proteinuria arising from glomerular or tubular lesions is a marker of chronic kidney disease that is likely to be progressive.


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Source: VETERINARY MEDICINE,
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