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Q: What are the current methods of screening for diabetic nephropathy?
A: Initial screening for microalbuminuria is recommended at diagnosis in patients with type 2 diabetes, and in persons with type 1 diabetes of 5 years or longer duration. Annual follow-up measurements are recommended thereafter. Three screening methods are available: 1) measurement of the microalbuminto-creatinine ratio in a random spot urine specimen; 2) 24-hour urine collection, which allows simultaneous measurement of creatinine clearance; and 3) timed, less than 24-hour collection (eg, overnight, or 4-hour samples). For many years, the mainstay of surveillance was measurement of albumin excretion in a 24-hour or timed urine specimen. Such measurements (especially the 24-hour collections) were cumbersome and notoriously inaccurate for large-scale population screening. A major advance in the field has been the validation of spot urine specimens for screening. Simultaneous measurement of microalbumin and creatinine concentrations in spot urine samples yields informative results when microalbuminuria is expressed as a ratio of creatinine excretion. A first-void or morning collection is preferable because of diurnal variation in albumin excretion. The normal range is a spot urine microalbumin concentration of <30 µg/mg creatinine, which is equivalent to <30 mg/24 h. The convenience of spot urine screening offers a great opportunity for disease surveillance during office visits. Because day-to-day variations occur in albumin excretion, it is prudent to obtain repeat (confirmatory) measurements.2
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