Microalbuminuria and hypertension

An elevated urinary albumin excretion (UAE) below the proteinuric level, i.e. microalbuminuria (MAU), has long been recognized as a marker of kidney disease and increased cardiovascular risk in both types of diabetes mellitus. Subsequent clinical evidence documented an association between MAU and other cardiovascular risk factors, target organ damage and risk of cardiovascular disease in the general population and in specific clinical contexts including essential hypertension. This article reviews the available evidence on the clinical value of MAU in subjects with essential hypertension. In these subjects, the reported prevalence of MAU ranges from about 4% to 46% across different studies and these differences may be explained by the huge intraindividual variability in UAE, age and ethnicity, discrepancies in the technique of measurement and different definitions of MAU. A direct and continuous association between UAE and blood pressure (BP) and left ventricular mass has been found in most studies. In contrast, it is not yet clear whether the association between UAE and other factors including age, gender, smoking, ethnicity, insulin resistance, lipids and obesity is independent or due to confounders, particularly BP. Several prospective studies disclosed an association between MAU and the risk of future cardiovascular disease. Of particular note, in some of these studies the incidence of major cardiovascular events progressively increased with UAE starting below the conventional MAU thresholds. Thus, besides being a direct risk factor for progressive renal damage, MAU can be considered a marker which integrates and reflects the long-term level of activity of several other detrimental factors on cardiovascular system. Antihypertensive treatment reduces UAE and such effect may be detected after just a few days of treatment. Among available antihypertensive drugs, angiotensin converting enzyme (ACE) inhibitors and the angiotensin II receptor antagonists seem to be superior to other antihypertensive drugs in reducing UAE. The dual blockade of the renin angiotensin system with an ACE inhibitor and an angiotensin II receptor antagonist is a new and promising approach to control UAE in hypertensive patients. Determination of MAU is recommended in the initial work-up of subjects with essential hypertension as suggested in the most recent European hypertension guidelines, even though, as upcoming evidence suggest, the periodic evaluation of this simple, inexpensive and predictive marker might be valuable and cost-effective.