SCREENING FOR MICROALBUMINURIA - WHICH MEASUREMENT

It now seems worth while to identify Type 1 diabetic patients with microalbuminuria, as improved blood glucose control and reduction of arterial blood pressure will slow if not prevent the progression to persistent proteinuria. Measurement of albumin excretion rate (AER) in a timed urine sample remains the gold standard for the definition of microalbuminuria, but is not a practical screening procedure. Thus attempts have been made to relate the albumin concentration or albumin:creatinine random or first morning urine samples to AER. There is a weak correlation of albumin concentration (r = 0.32 to 0.68) and albumin:creatinine ratio (r = 0.43 to 0.54) in a random urine sample with AER, and low sensitivity and specificity of a variety of different albumin concentrations and albumin:creatinine ratios to predict microalbuminuria. The correlation of albumin concentration (r = 0.86 to 0.90) and albumin:creatinine ratio (r = 0.74 to 0.91) in an early morning urine sample with AER is stronger. Measurement of albumin:creatinine ratio in an early morning urine sample appears to be the most reliable method of screening for microalbuminuria, with sensitivity of 88 to 100 % and specificity 81 to 100 % depending on the cut-off ratio chosen and the definition of microalbuminuria used. If the albumin:creatinine ratio in an early morning urine sample is less-than-or-equal-to 3.5 mg mmol-1, the patient can be classed as normoalbuminuric and re-screened annually. If the ratio is greater-than-or-equal-to 10.0 mg mmol-1, confirmation of microalbuminuria should be sought in a timed urine collection and appropriate therapy begun. If the ratio is 3.6 to 9.9 mg mmol-1, there is a high risk of more rapid progression to definite microalbuminuria and the patient should be re-screened more frequently.