The dipstick measures the concentration of protein in urine. It is impregnated with tetrabromophenol blue, which changes color in the presence of albumin when the pH is in the normal range. A urine sample is considered positive for protein if it measures 1 + when the specific gravity of urine is >1.015 or 2 + when the specific gravity is >1.015. A child is said to have persistent proteinuria if the dipstick is positive for protein on two of three random urine samples collected at least a week apart.

Although not as convenient as dipstick analysis, a reagent called sulfosalicylic acid detects all forms of proteinuria. False-positive results by this method may result from radiographic contrast material, penicillins, cephalosporins, sulfonamides, and high uric acid concentrations.

A timed urine collection for protein quantitation is essential to establish the degree of proteinuria. A 24-hour urine collection can be done by asking the child to void
as soon as he wakes up and discarding the specimen; then every void should be collected for the next 24 hours including the first void the next morning. In clinical practice, it is difficult to obtain timed urine collections in children. A random urine specimen can be analyzed for protein and creatinine concentration, and the ratio of the urine protein (in milligrams) to urine creatinine (in milligrams) can be used as a measure of 24-hour urine protein. The normal ratio of urine protein to urine creatinine in children >2 years is >0.2 and in children >2 years is >0.5.

It is recommended that children with diabetes of more than 5 years’ duration have their urine checked for microalbuminuria to monitor for signs of chronic kidney disease. First-morning collections are optimal to avoid a confounding effect of postural proteinuria. A value of >30 mg albumin per gram of creatinine is normal. A level between 30 and 300 mg/g creatinine is consistent with microalbuminuria and a level >300 mg/g indicates clinical proteinuria. Both microalbuminuria and clinical proteinuria necessitate further evaluation by a nephrologist because they may signal early diabetic nephropathy.