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You’ve just been to the doctor. He found sugar in your urine. But your blood sugars are usually in the 90s fasting, and around 140 mg/dl after meals, at least when you check. And isn’t the renal threshold, or the level of blood glucose above which kidneys fail to reabsorb, and thus spill glucose into urine, often stated as 180 mg/dl?
Might your sugars be going higher without you knowing it?
In addition to home testing, a simple A1C test might indicate that fact.1
However, there’s the possibility you could be spilling glucose at levels below 180 mg/dl. A fair amount of normal variability exists in the renal threshold – both among individuals and within an individual – which makes urine testing not a very dependable tool for detecting a high blood glucose.
Here are a few references I found to that effect:
, Diabetes Care, 2004
Reasons why the use of urine glucose testing to estimate blood glucose concentrations in diabetes management is undesirable include the following: Although the renal threshold for glucose in healthy adults corresponds to a plasma glucose concentration of ~180 mg/dl (10 mmol/l), there is wide individual variation. Of particular importance are findings that adults, especially those with long-standing diabetes, may have substantial increases in this threshold, resulting in underestimation of the blood glucose level. Conversely, children and, particularly, pregnant women may have very low or variable renal thresholds, resulting in overestimation of the blood glucose level. Fluid intake and urine concentration affect urine test results. The urine glucose value reflects an average level of blood glucose during the interval since the last voiding and not the level at the time of the test. A negative urine glucose test does not distinguish between hypoglycemia, euglycemia, and mild or moderatehyperglycemia. Thus, urine glucose testing is of limited value in preventing hypoglycemia and hyperglycemia. Urine glucose testing, which uses a color chart with which the test strip color is compared, is less accurate than capillary blood glucose monitoring, which typically uses a digital readout from a reflectance meter. Some drugs interfere with urine glucose determinations. Evaluation of urine dipsticks reveals high imprecision at low glucose concentrations. Manufacturers claim that the test strips are positive if urinary glucose concentrations are 100 mg/dl or greater, but the data indicate this does not always occur.”
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