Methodology of screening for albuminuria.

Albuminuria has been recognized as a marker of generalized vascular endothelial damage. Even low levels, called micro-albuminuria, independently predict poor cardiovascular and renal outcome in subjects with diabetes, hypertension, but also in non-diabetic, non-hypertensive individuals [1–4]. These complications consume a large proportion of health-care budgets. Recently, several nephrological societies, such as the ASN and ISN, proposed to initiate screening for albuminuria to identify subjects at high risk, who might benefit from preventive treatment [5,6]. Screening should be aimed at subjects with hyperten-sion, diabetes and chronic kidney disease; however, mass screening of the general population has also been advocated. Although it is recommended to start screening for albuminuria, there are questions that remain unanswered. For instance, should screening be based on assessment of albuminuria in 24 h urine samples, or are morning urine samples sufficiently reliable? Due to the diurnal rhythm in urinary albumin excretion, it has been assumed that 24 h albuminuria should be regarded as the gold standard. Albumin concentration or the albumin:creatinine ratio in spot urine samples may be less appropriate, because they vary in any given individual, depending on the point of time during the day that they are collected. The definitive answer, in the discussion as to which measure of urinary albumin excretion should be used in clinical practice, should be given by observational studies showing which of the three performs best in predicting cardiovascular and renal endpoints. One such study investigated this issue. Surprisingly, it showed that protein:creatinine ratio in a spot sample is even more reliable than a 24 h urinary protein excretion in predicting decline in GFR and progression to end-stage renal failure, in subjects with non-diabetic renal disease [7]. Unfortunately, albumi-nuria was not measured. Given the paucity of data, measurement of 24 h urinary albumin excretion should remain the gold standard, at least in research areas, until other data come available. Collecting a 24 h urine sample is time-consuming and inconvenient, and therefore not feasible for population screenings. Another possibility for organizing population screening is by pre-screening, based on albuminuria assessment in spot urine samples. Only subjects that score a value above a certain cutoff are then asked to collect 24 h urine samples for confirmation of the presence of micro-albuminuria. This practice may minimize the number of subjects that need to collect 24 h urines. Jafar et al. [8] tested this approach in subjects recruited from the general population in Pakistan. …