500 mg/g or
3000 mg/g. These
probabilities can help clinicians decide whether to order more
precise measurements of urinary protein.Because urine dipsticks are used widely to screen urine samples, we need to know how closely dipstick protein measurements correlate with directly measured urinary protein-creatinine (UPC) ratios. Researchers analyzed 2098 urine samples that were submitted to a hospital laboratory for simultaneous dipstick urinalysis and UPC ratio. Urine specific gravity (SG) also was factored into the analysis, since a given dipstick protein value represents a higher rate of protein excretion in dilute than in concentrated specimens.
The researchers created two 8-by-5 tables that displayed 40 combinations of urine SG values (ranging from 1.005 to 1.040) and dipstick protein values (0, 10, 30, 100, and >300 mg/dL). Each cell of one table provided the proportion of patients with UPC ratios of 500 mg/g or greater (overt proteinuria), and each cell of the other table provided the proportion of patients with UPC ratios of 3000 mg/g or greater (nephrotic-range proteinuria). For example, a patient with 0 mg/dL dipstick protein level and 1.020 SG has a 2% probability of overt proteinuria and 0% probability of nephrotic-range proteinuria. In contrast, a patient with 300 mg/dL dipstick protein level and 1.020 SG has a 98% probability of overt proteinuria and 62% probability of nephrotic-range proteinuria.
Using the data from this study, the authors provide a "proteinuria
calculator": One enters the dipstick protein level and SG
values, and the calculator displays the probability that the protein-creatinine
ratio is
500 mg/g or
3000 mg/g. These
probabilities can help clinicians decide whether to order more
precise measurements of urinary protein.
Reference:
Constantiner M et al. A dipstick protein and specific gravity algorithm accurately predicts pathological proteinuria. Am J Kidney Dis 2005 May; 45:833-41.