The Best Way to Detect Elevated Albuminuria

BACKGROUND: It has been reported that first morning specimens are more reliable than random spot specimens to assess 24-hour urinary albumin excretion rate (UAER), especially if albuminuria is expressed as albuminuria to creatininuria ratio. We aimed to investigate the influence of (a) posture and activity and (b) the units to best estimate 24-hour albuminuria. METHODS: In this retrospective study, 24-hour UAER was compared to 60 min 'supine' and 90 min 'activity' albuminuria in 124 patients tested for resistant hypertension. The ability to adjust urinary albumin concentration (UAC) to creatininuria (ACR) or to collection duration (tAER) values in order to increase the reliability of albuminuria values was also analyzed. RESULTS: Compared to 24-hour UAER, UAC (mg/l), tAER (μg/min) and ACR (mg/mmol) during the supine period had a similar concordance rate in normo-, micro- and macroalbuminuric patients. The UAC in the supine period was well related to 24-hour UAER. However, UAC almost doubled during activity. Adjustment to creatininuria improved the correlation between albuminuria during both periods and 24-hour UAER, but mainly during the activity period. CONCLUSIONS: Our results confirm that UAC is dependent on physical activity. Correction of UAC by creatininuria (ACR) provides a satisfactory estimation of 24-hour UAER. Thus, for practical reasons, it is advisable to use ACR, where no differences appear to exist, whether a supine urine sample or an activity urine sample is obtained.