Glucose in urine: what a positive result means

The kidneys filter the blood and then reclaim useful substances, including glucose. Patient.info explains that three membrane proteins in the proximal tubule are responsible for reabsorbing glucose, and that virtually all the glucose filtered is taken back, so the amount left in the urine is normally too small to be detected by standard techniques. Glycosuria is the term for glucose present in urine in detectable amounts.

There are two basic causes. One is that the blood glucose is so high that the tubules cannot reabsorb it all. The other is that the tubules fail to reabsorb glucose at a normal blood level, a situation called renal glycosuria. The blood level at which glucose starts to spill into the urine is the renal threshold, which under normal circumstances is around 10 mmol/L according to Patient.info.

High blood glucose is the most important cause to exclude. Patient.info says this is usually indicative of impaired glucose tolerance or frank diabetes, and that other conditions that raise blood glucose include an overactive thyroid, acromegaly, Cushing's syndrome (including corticosteroid drugs), severe anxiety, very rapid gastric emptying after some stomach operations and severe illness, when stress hormones raise glucose beyond the threshold. A large sugary intake can also transiently cause glycosuria in a person without diabetes.

The NHS explains that diabetes is a condition that causes your blood glucose level to become too high, either because the body does not make enough insulin or because it does not work properly. People with pre-diabetes have glucose above the normal range but not high enough to be called diabetes.

Causes in which blood sugar is normal include pregnancy, which lowers the renal threshold because of increased kidney blood flow; Fanconi syndrome, a tubular problem; and renal glycosuria, a rare inherited disorder that Patient.info says is usually asymptomatic and in most affected individuals needs no treatment, although some may go on to develop diabetes. SGLT2 inhibitor medicines used for diabetes cause a dose-dependent glycosuria, and the article lists a range of rare secondary causes such as Lowe syndrome, cystinosis and Wilson's disease.

Glucose in urine causes no symptoms of its own. What matters is the cause. The NHS lists these common symptoms of diabetes:

• Feeling thirsty all the time.

• Peeing more than usual.

• Feeling very tired.

• Losing weight without trying.

A positive dipstick is a prompt for further testing, not a diagnosis. Patient.info explains that glycosuria is diagnosed by laboratory tests showing glucose in the urine with normal or low blood glucose in renal glycosuria, and that standard dipsticks use glucose oxidase, which is specific for glucose. In practice, a GP will usually check blood glucose or HbA1c, look at your symptoms, medicines and family history, and may also check kidney function.

If the cause is diabetes, the NHS describes treatment that depends on type: insulin for type 1, and lifestyle changes with or without medicines such as metformin for type 2. Because not everyone with diabetes has symptoms, the NHS stresses the importance of being checked if you are at higher risk.

If you are pregnant and glucose is found in your urine, tell your midwife or GP. Patient.info points to NICE guidance on testing for gestational diabetes, and says a urine dipstick is not a reliable test for it.

The NHS says that diabetes can increase the chance of other health problems, including kidney problems, and that complications are linked to high blood glucose, so good management can lower the chances. Where renal glycosuria is the explanation, the outlook is generally good. Regular reviews through your GP or diabetes team are the norm.

Both NHS and private providers can carry out urine dipsticks and blood glucose tests. Home urine strips are sometimes sold, but a positive strip should be confirmed with a blood test through a GP or pharmacist-led service.