Urine For GTT

Function

The Urine Glucose Tolerance Test (GTT) is performed in conjunction with the oral blood glucose tolerance test. It measures the presence of glucose in the urine at specific intervals after a patient consumes a concentrated glucose beverage. Normally, the kidneys reabsorb almost all glucose from the filtrate; glucose only appears in the urine when blood levels exceed the 'renal threshold.'

Why it is Ordered

This test is primarily used to screen for gestational diabetes in pregnant women or to evaluate patients with suspected type 2 diabetes or renal glycosuria. It helps determine if the kidneys are leaking glucose at lower-than-expected blood sugar levels or if blood sugar is spiking so high that the kidneys cannot keep up.

Associated Conditions

• Diabetes Mellitus: Persistent glycosuria during the test indicates high systemic blood sugar.
• Gestational Diabetes: Critical for identifying pregnancy-induced glucose intolerance.
• Renal Glycosuria: A condition where glucose is excreted in the urine despite normal blood glucose levels due to kidney tubule dysfunction.
• Cushing’s Syndrome: Excess cortisol can lead to glucose intolerance.

Clinical Insight

While blood glucose testing is the gold standard, urine testing provides historical data on the 'spillover' effect during the test period. If glucose is found in the urine while blood levels are normal, it suggests a kidney-specific issue rather than a metabolic one.