on 15-Nov-2020 (Sun)

Total urinary protein excretion in the normal adult should be less than 150 mg/day.

In this study of 1011 patients, of whom 68 had a kidney biopsy, the ratio of the urine albumin to total protein concentration was generally less than 0.4 in patients with tubular or overflow proteinuria and greater than 0.4 in patients with predominantly glomerular proteinuria

In one study of more than 2000 patients, for example, a urine dipstick for proteinuria of 2+ or higher was predictive of significant proteinuria (urine protein-to-creatinine ratio (UPCR) greater than or equal to 500 mg/g) regardless of the specific gravity; however, a urine dipstick for proteinuria of trace or 1+ was only predictive of significant proteinuria if the specific gravity was 1.025 or less [9]

False positive urine dipstick results may occur in the following settings:

● After the use of iodinated radiocontrast agents [11]. Thus, the urine should not be tested for protein with the standard dipstick for at least 24 hours after a contrast study.

● With a highly alkaline urine (pH greater than 8) [12,13].

● In the presence of gross hematuria and a urocrit (the percent of urine volume comprised of red blood cells) greater than 1 percent [14].

● When specific antiseptics (eg, chlorhexidine, benzalkonium) are used for clean-catch urine samples [15]

As a general rule in adults under the age of 50 years, daily creatinine excretion should be 20 to 25 mg/kg (177 to 221 micromol/kg) of lean body weight in men and 15 to 20 mg/kg (133 to 177 micromol/kg) of lean body weight in women. From the ages of 50 to 90 years, there is a progressive 50 percent decline in creatinine excretion (to approximately 10 mg/kg in men, lower in women) due primarily to a fall in muscle mass. Formulas that incorporate race and weight with or without serum phosphorous in addition to age and sex may improve the estimation of creatinine excretion

However, the UPCR may produce errors when applied to the individual patient, especially in those who consistently excrete much more (or less) than 1 g/day of creatinine (which is typical for younger men and many younger women) or in those who are losing or gaining muscle mass

The UPCR is useful on the population level because the average 24-hour urine creatinine excretion for the population is assumed to be approximately 1000 mg/day (8.84 mmol/day) per 1.73 m².

● In individuals with large muscle mass, in whom creatinine excretion may be much higher than 1000 mg/day, the UPCR (or UACR) will underestimate proteinuria.

● In a cachectic patient or a patient with small muscle mass, in whom creatinine excretion may be much lower than 1000 mg/day, the UPCR (or UACR) will overestimate proteinuria

In addition, all patients with persistent proteinuria that is greater than 500 mg/day for total protein (or an estimated protein excretion rate [ePER] greater than 0.5 g/day) or greater than 300 mg/day for albumin (or an estimated albumin excretion rate [eAER] greater than 300 mg/day) should be referred to a nephrologist for decisions regarding further evaluation and management (eg, kidney biopsy, discussed below)