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

Abstract

The prevalence of raised Na+/Li+ countertransport (CT) activity (>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 <20 μg/min (N = 121), microalbuminuria as AER between 20 and 150 μg/min (N = 35) and macroalbuminuria as AER ≥ 150 μg/min (N = 29). The prevalence of elevated Na+/Li+CT (>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; r(s) = 0.37, P < 0.001) and AER (r(s) = 0.38, P < 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 (χ2 = 9.7, P < 0.002). Elevated Na+/Li+CT activity is more prevalent in IDDM patients with proteinuria and is rare in long-standing normoalbuminuric patients; the risk of proteinuria increases with increasing Na+/Li+CT rates; blood glucose control and Na+/Li+CT appear to interact in determining proteinuria.