Renal threshold for glucose in non-insulin-dependent diabetic patients

Measurement of glycosuria is still widely used for home monitoring of glycaemic control in non-insulin-dependent diabetes (NIDDM). This method has been criticized because the renal threshold for glucose (RTglu) varies between subjects. In order to evaluate the validity of RTglu by measuring corresponding measurements of blood and urine glucose in NIDDM patients, we studied the blood/urine glucose relationship in 24 NIDDM patients. RTglu estimated from 75 contemporary blood and urine glucose concentrations measured at home by each patient (h-RTglu) was compared with RTglu measured by a hyperglycaemic glucose clamp (c-RTglu). H-RTglu and c-RTglu, being 7.6 mmol/1 (range 5.5–12.4) and 10.3 mmol/1 (6.2–12.3) respectively ( P < 0.005), were weakly correlated ( R( S) = 0.35, P = 0.15). In conclusion, c-RTglu varies two-fold between NIDDM patients. RTglu detected by home monitored urine and blood glucose determinations underestimates the true RTglu, probably due to the splay phenomenon. However, the method for detection of RTglu used by us seems of clinical relevance, since it reflects the individual blood glucose level at which glucose is detectable in the urine.