Measurement of urinary albumin excretion (UAE) may be done on a morning urinary sample or on a 24 hours-urine sample. Values defining microalbuminuria are: 24 hour-urine sample: 30-300 mg/24 hours; morning urine sample: 20-200 mg/ml or 30-300 mg/g creatinine or 2.5-25 mg/mmol creatinine (men) or 3.5-35 mg/mol (women). Timed urine sample: 20-200 microg/min. The optimal use of semi-quantitative urine test-strip is not clearly defined. It is generally believed that microalbuminuria reflects a generalized impairment of the endothelium; however, no definite proof has been shown in humans.
In diabetic subjects: Microalbuminuria is a marker of increased risk of cardiovascular (CV) and renal morbidity and mortality in type 1 and type 2 diabetic subjects. The increase in UAE during follow-up is also a marker of CV and renal risk in type 1 and type 2 diabetic subjects; its decrease during follow-up is associated with lower risks.
In no diabetic subjects: Microalbuminuria is a marker of increased risk for diabetes mellitus, deterioration of the renal function, CV morbidity and all-cause mortality. It is a marker of increased risk for the development of hypertension in normotensive subjects, and is associated with unfavorable outcome in patients with cancer and lymphoma. Persistence or elevation of UAE overtime is associated with deleterious outcome in some hypertensive subjects. Measurement of UAE may be recommended in hypertensive subjects with one or two CV risk factors in whom CV risk remains difficult to assess, and in those with refractory hypertension: microalbuminuria indicates a high CV risk and must lead to strict control of arterial pressure. Studies focused on microalbuminuria in non-diabetic non-hypertensive subjects are limited; most of them suggest that microalbuminuria predicts CV complications and deleterious outcome as it is in diabetic or hypertensive subjects. Subjects with a history of CV or cerebrovascular disease have an even greater CV risk if microalbuminuria is present than if it is not; however, in all cases, therapeutic intervention must be aggressive regardless of whether microalbuminuria is present or not. It is not recommended to measure UAE in non-diabetic non-hypertensive subjects in the absence of history of renal disease. Monitoring of renal function (UAE, serum creatinine and estimation of GFR) is annually recommended in all subjects with microalbuminuria.
Management: In patients with microalbuminuria, weight reduction, sodium restriction (<6 g/day), smoking cessation, strict glucose control in diabetic subjects, strict arterial pressure control are necessary; in diabetic subjects: use of maximal doses of ACEI or ARB are recommended; ACEI/ARB and thiazides have synergistic actions on arterial pressure and reduction of UAE; in non diabetic subjects, any of the five classes of antihypertensive medications (ACEI, ARB, thiazides, calcium channel blockers or betablockers) can be used.