Prevalence of raised sodium-lithium countertransport activity in type 1 diabetic patients.

The prevalence of raised Na+/Li+ countertransport (CT) activity (greater than 0.41 mmol/liter RBC/hr) was assessed in 185 consecutive insulin-dependent diabetic patients attending an outpatient diabetic clinic. Normoalbuminuria was defined as an overnight albumin excretion rate (AER) of less than 20 micrograms/min (N = 121), microalbuminuria as AER between 20 and 150 micrograms/min (N = 35) and macroalbuminuria as AER greater than or equal to 150 micrograms/min (N = 29). The prevalence of elevated Na+/Li+CT (greater than 0.41 mmol/liter RBC/hr) was 21.5, 42.8 and 51.7% (P = 0.0005), in patients with normo-, micro- and macroalbuminuria, respectively. In the whole group, Na+/Li+CT was significantly related to mean blood pressure (MBP; rs = 0.37, P less than 0.001) and AER (rs = 0.38, P less than 0.001). In a multiple regression analysis the significant correlates of AER, as a continuous variable, or of proteinuria (micro + macroalbuminuria), as a categorical variable, were Na+/Li+CT, MBP, duration of diabetes and glycosylated hemoglobin (HbA1). The frequency of normoalbuminuric patients with high Na+/Li+CT activity fell with duration of diabetes. The risk of proteinuria was significantly greater in patients with raised Na+/Li+CT compared to those with Na+/Li+CT within the normal range (odds ratio 3.8, 95% CI, 1.9 and 7.8). A relative excess of patients with proteinuria (micro + macroalbuminuria) was found in the group with elevated Na+/Li+CT and HbA1 above the median value (8.05%) of the whole population (chi 2 = 9.7, P less than 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)