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


WHEN SHOULD I MEASURE ALBUMIN IN THE URINE?

Albumin is the major protein found in canine and feline urine, and low-level albuminuria (microalbuminuria), which is defined as concentrations of albumin in the urine that are greater than normal but below the limit of detection with conventional dipstick urine protein screening methodology (i.e. < 30 mg/dl), may be present. Thus, albuminuria testing (e.g. E.R.D.-HealthScreen Canine and Feline Urine Tests—Heska) or a quantitative immunoassay at a reference laboratory (e.g. Heska, Antech) is recommended

1. If the urine dipstick or sulfosalicylic acid screening tests for proteinuria produce equivocal or conflicting results or you suspect a false positive result

2. If screening tests are negative in apparently healthy older dogs and cats, and you would like to obtain more sensitive screening test results

3. If screening tests are negative in apparently healthy young dogs and cats with a familial risk for developing proteinuric renal disease, and you would like to obtain more sensitive screening test results

4. As a screening test in cats (or a urine protein:creatinine ratio; see below), inasmuch as the dipstick and sulfosalicylic acid screening tests have poor specificity for feline albuminuria

5. If a previous albuminuria test result was positive and you want to monitor the patient for persistence or progression of albuminuria.

Albuminuria can result from prerenal and postrenal disorders; therefore, it is important to localize the source of albuminuria as discussed above.

WHEN SHOULD I MEASURE A URINE PROTEIN:CREATININE (UP/C) RATIO?

Persistent proteinuria/albuminuria of suspected renal origin should be quantitated using the UP/C ratio both at baseline and subsequent to treatment.

Because persistent proteinuria can remain constant or change in magnitude over time, use the UP/C ratio to evaluate disease progression or treatment response. The UP/C ratio accurately reflects the amount of protein excreted in the urine over 24 hours. Normal UP/C ratios are < 0.2 in dogs and cats; values between 0.2 and 0.4 in cats and 0.2 and 0.5 in dogs are considered borderline, and values > 0.4 in cats and > 0.5 in dogs are considered abnormal.2

You need to interpret changes in the magnitude of proteinuria in conjunction with the patient's serum creatinine concentration because proteinuria may decrease in patients with progressive renal disease as the number of functional nephrons decreases. Decreasing proteinuria and a stable serum creatinine concentration suggest improving renal function, whereas decreasing proteinuria and an increasing serum creatinine suggest disease progression.

WHY SHOULD I MONITOR PROTEINURIA?

Patients with moderate to severe proteinuria may exhibit hypoalbuminemia, edema, ascites, hypercholesterolemia, hypertension, and hypercoagulability. However, another crucial reason to be concerned about proteinuria is that it is associated with renal glomerular and tubulointerstitial damage and progressive nephron loss in dogs and cats.2

In cats with naturally occurring chronic kidney disease, fairly mild proteinuria (UP/C ratio > 0.2) was a negative predictor of survival.3 In cats with systemic hypertension, proteinuria has been associated with decreased survival time.4 And in geriatric cats, proteinuria has been associated with the development of azotemia.5

In dogs with naturally occurring chronic kidney disease, the relative risk of uremic crises and mortality was about three times higher in dogs that had a UP/C ratio > 1.0 compared with dogs that had a UP/C ratio < 1.0.6

Therefore, veterinarians should be concerned about testing and monitoring for proteinuria (and systemic hypertension) in their patients so that treatment may be instituted as early as possible.

Although renal proteinuria is associated with azotemic renal disease progression, at this point we don't know if proteinuria is simply a marker of severe chronic kidney disease that is more likely to progress or whether it mediates progressive renal injury.2 If proteinuria mediates progressive renal injury, treatments that reduce proteinuria are likely to be renoprotective and improve patients' survival.

To read the ACVIM consensus statement on assessing and managing proteinuria in dogs and cats, go to http://onlinelibrary.wiley.com/doi/10.1111/j.1939-1676.2005.tb02713.x/pdf.

Gregory F. Grauer, DVM, MS, DACVIM
College of Veterinary Medicine
Kansas State University
Manhattan, KS 66506

Editor's note: Dr. Grauer has previously served as a consultant for Heska.


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Source: VETERINARY MEDICINE,
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