[Urinary albumin excretion during the night in essential arterial hypertension]

The value of nocturnal minute-by-minute urine was analyzed for the detection of microalbuminuria in high blood pressure.

Urinary albumin excretion (UAE) was measured by immunonephelometry in 70 patients with essential arterial hypertension (34 males, mean age 44 +/- 5 years, body mass index [BMI] 28 +/- 4, clinical blood pressure [BP] 157 +/- 12/97 +/- 7 mmHg) and 12 healthy normotensive controls (5 males, mean age 38 +/- 4 years, BMI 27 +/- 3; clinical BP 126 +/- 12/79 +/- 5 mmHg). Both 24 hours urine as well as nocturnal urine were collected over 2 days. The intraindividual variability was evaluated by calculation of the intraclass correlation coefficient and by the Bland and Altman method.

Mean 24-hour UAE was 24.7 +/- 41.9 micrograms/min, greater than nocturnal urine (17.7 +/- 32.8 micrograms/min) (p < 0.05). The UAE rate was significantly greater in the hypertensive patients than in the controls (p < 0.01) for both the 24-hour and nocturnal urine. The intraindividual variability estimated as the percentage of repeatability was 35% for 24-hour UAE and 43% for nocturnal UAE, being slightly higher values than those observed in the controls. Microalbuminuria was detected in 17 (24%) of the patients in 24-hour samples while in the nocturnal urine 12.12 or 10 patients were found according to whether the threshold considered was 14 micrograms/min, 14.9 micrograms/min or 20 micrograms/min, respectively. While the specificity in nocturnal minute-by-minute urine was 98% and the positive predictive value was 0.91 for any of the thresholds considered, sensitivity ranged from 59% for the higher threshold (20 micrograms/min) to 70% for the lower threshold (14 micrograms/min).

The determination of microalbuminuria in minuted nocturnal urine in patients with essential arterial hypertension is less sensitive than that determined in 24-hour urine.