Microalbuminuria Varies by Race in Healthy Teens
By Todd Neale, Staff Writer, MedPage Today
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco
Healthy black teens have about a 10% higher rate of urine albumin excretion (AER) than whites of similar age (P=0.006), researchers here found.
This study found that normotensive black adolescents had a higher rate of albumin excretion than their white counterparts, which might indicate an increased risk for developing hypertension.
"If these findings are confirmed, high-normal AER may be considered a risk factor that prompts early intervention for blacks with [blood pressures] in the prehypertensive range," concluded Gregory Harshfield, Ph.D., of the Medical College of Georgia, and colleagues in the February issue of Hypertension.
Accounting for much of the racial difference, they said, was the fact that black females had about a 22% higher AER than white females (P=0.036).
Most of the participants in this study excreted sodium normally during a stressful activity, the researchers said, but 26% of blacks and 21% of whites experienced impaired stress-induced pressure natriuresis.
In blacks, those who were impaired had a significantly higher albumin excretion rate than those who were not (P=0.024). A similar relationship was not seen in whites.
AER showed a significant positive correlation with systolic blood pressure only in black males, with the highest associations occurring during the stress period (P=0.001).
"The demonstration here of relative elevation of AER in normotensive black adolescents as compared with white youths is noteworthy," the researchers said. "The link between higher [blood pressure] and impaired sodium natriuresis shown here supports a propensity to develop sustained hypertension with age."
Racial and gender differences in albumin excretion rate have been found in studies of adults, but no data are available for healthy youths, the researchers said.
So they evaluated AER in teens participating in a study of stress-induced pressure natriuresis. Participants included 317 normotensive teenagers (216 blacks and 101 whites; 155 males and 162 females) ages 15 to 18.
The black participants were significantly younger and shorter, and had higher blood pressure (P=0.001 for all) than whites; they also had significantly higher body mass indices (P=0.05).
Males had higher systolic blood pressure and sodium and creatinine excretion than females (P=0.001 for all).
For three days before the study, the researchers provided each participant with a controlled diet and verified compliance with overnight urine collections.
On the fourth day, participants underwent a five-hour test. It consisted of two hours of rest, one hour of stress induced by competitive video game play for a cash prize, and then two more hours of rest. Urine samples were collected every hour.
AER was measured after the first hour of rest.
When looking at the effects of race and sex on albumin excretion adjusted for creatinine excretion, the researchers found that the black adolescents had a significantly greater albumin to creatinine ratio than whites (1.87 ± 0.8 versus 1.65 ± 0.8 ìg/mg of creatinine, P=0.01).
This ratio was also higher in girls than in boys (2.01 ± 0.7 versus 1.58 ± 0.8 ìg/mg of creatinine, P0.0001), as a result of lower levels of creatinine excretion in females at baseline.
During the stress period, males had greater changes in both diastolic (P=0.05) and systolic (P=0.001) blood pressure and sodium excretion (P=0.05) than females.
The heart rates of the white participants increased significantly more than those of blacks (P=0.05).
The authors noted some limitations of the study, including the fact that they could not exclude the possibility of a postural effect on albumin excretion because they did not use first-morning urine samples.
Also, they noted, only one sample was analyzed for each participant, so intrasubject variability in albumin excretion could have affected the findings.
Furthermore, the use of spot measurements of albumin to creatinine ratio may have over- or underestimated albumin excretion. Age and pubertal development may also affect albumin excretion, they said.
Nonetheless, "these findings suggest that albumin excretion may be a marker for a population at increased risk for the development of vascular and renal injury even before the manifestation of hypertension," the researchers concluded.
The study was supported by grants from the National Heart, Lung, and Blood Institute.
The authors made no disclosures.
Hanevold C, et al "Racial differences in microalbumin excretion in healthy adolescents"Hypertension 2008; DOI: 10.1161/HYPERTENSIONAHA.107.098095.
www.medpagetoday.com February 29, 2008
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