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urine protein/creatinine ratio

December 8, 2012
The protein/creatinine ratio is used to estimate the urine protein excretion rate once patients have overt proteinuria. Normal individuals excrete < 150 mg/day of total protein in the urine, including a very small amount of albumin (< 20 mg/day) that’s well below the detection limit of the urine dipstick (300-500 mg/day). By the time the dipstick test turns positive, the urine protein excretion rate is > 300 mg/day, and you’re dealing with what’s called albuminuria or overt proteinuria.

While albuminuria or proteinuria indicates a disease state, microalbuminuria (30-300 mg/day) identifies patients at risk. It’s important to understand that microalbuminuria can occur even if the total urine protein excretion is normal. Regardless of the mechanism, microalbuminuria reflects a generalized endothelial dysfunction that may predispose to both cardiovascular disease and progression of kidney disease. So it’s a useful marker to identify high-risk patients early on and consider intervention. Because measuring urinary albumin in a timed sample is often cumbersome and inaccurate, a spot albumin/creatinine ratio is a good stand-in — it correlates well and is a simple test to perform and monitor.

The protein/creatinine ratio, on the other hand, helps to guide therapy once patients have overt proteinuria. The two conditions, then, are at opposite ends of the spectrum of abnormal urine protein excretion. Checking for microalbuminuria is a screening test that should be performed in healthy individuals, but there’s no point in screening a patient who already has a known dysfunction, i.e. proteinuria.


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