Increased Na+/Li+ countertransport activity may help to identify type 1 diabetic adolescents and young adults at risk for developing persistent microalbuminuria

OBJECTIVE - To evaluate whether erythrocyte sodium-lithium countertransport (Na+/Li+ CT) activity may identify adolescents and young adults with child hood-onset of type 1 diabetes to be at greater risk to develop persistent m icroalbuminuria and incipient diabetic nephropathy RESEARCH DESIGN AND METHODS - In January 1989, Na+/Li+ CT was measured in 1 70 normoalbuminuric diabetic adolescents and young adults (age 12-23 years, onset of diabetes before age 18 years; duration of diabetes longer than 7 years). Participants were clinically examined at baseline and biennially th ereafter. Na+/Li+ CT activity was measured every 2 years during the 8-year follow-up period. Na+/Li+ CT activity was measured also in parents of diabe tic offspring. RESULTS - Over 8 years. 18 (10 male, 8 female) out of 170 patients (10.5%) developed persistent microalbuminuria; no patient developed overt nephropat hy The risk of developing microalbuminuria was higher in children with incr eased Na+/Li+ CT (using 300 mu mol . 1 erythrocytes(-1) . h(-1) as the arbi trary cutoff point) (group 1) compared with those with normal Na+/Li+ CT at the beginning of the study (group 2) (18.98 vs. 3.29%, P < 0.01; sensitivi ty 96.7%; specificity 57.9%). Sex did not influence predictive value, sensi tivity, or specificity Na+/Li+ CT was not significantly correlated with HbA (1c) or duration of type 1 diabetes. The percentage of offspring with both parents having Na+/Li+ CT activity above the median values was significantl y higher in patients in group 1 than in group 2. The odds ratio for the occ urrence of microalbuminuria after adjustment for confounding variables (alb umin excretion rate [AER], sex, HbA(1c), mean blood pressure, cholesterol, triglycerides) in type 1 diabetic adolescents with elevated baseline erythr ocyte Na+/Li+ CT was 4.5 (95% CI of 2.1-11.4). CONCLUSIONS - These results confirm those of previous studies and suggest t hat Na+/Li+ CT may be one of the predictors and risk factors for incipient diabetic nephropathy in adolescents and young adults with onset of diabetes during childhood. Persistently increased Na+/Li+ CT activity may help to i dentify normotensive, normoalbuminuric patients with type 1 diabetes who ar e predisposed to develop microalbuminuria and incipient diabetic nephropath y.