Glycosuria

What is Glycosuria?

The term glycosuria or glucosuria indicates the presence of glucose in the urine. Usually, the kidneys absorb the blood glucose back into the bloodstream and it does not allow the glucose to be excreted. However, in a condition like diabetes mellitus, the kidneys are not able to reabsorb the glucose and some of it is lost in the urine and leads to glycosuria. The loss of glucose in urine also results in loss of water due to excessive urine production (diuresis), leading to dehydration of the body. The most common cause of glycosuria in our body is Diabetes Mellitus.

Most urine tests for sugar are done using standard 'dip-stick or a strip' and are used more as a screening test or for self-monitoring of diabetes rather than as a definitive test for diagnosis. A blood test will be required for the diagnosis of diabetes.

Nephrons are the smallest functional units of kidneys. Blood flows from the arteriole into the kidney's special capillaries called glomerulus. These capillaries are surrounded by a capsule called Bowman's capsule which absorbs the filtrate - a mixture of water, solutes like glucose, sodium, potassium and amino acids and waste products such as urea. Some of these solutes, including glucose, are reabsorbed back into the bloodstream. The nephrons are able to take back sugar from the filtrate only up to a certain level of glucose concentration in the filtrate. When the blood glucose level exceeds 160 to 180 milligram per deciliter (mg/dL), the tubules cease to absorb the glucose back into the bloodstream and this filtrate along with glucose is excreted in the urine. This is called renal threshold or RTG. The rate at which glucose is reabsorbed into the bloodstream from the filtrate is called glucose reabsorption rate.

When the blood glucose level exceeds about 160 - 180 mg/dl, there is a saturation of the reabsorbed filtrate and glucose is excreted in urine.

Causes of Glycosuria

• Diabetes mellitus: The lack of insulin in the blood elevates the glucose levels. When there is too much glucose in the blood, the kidneys are not able to reabsorb the sugar back into the bloodstream, allowing some of it to be excreted in the urine.
• Pregnancy: or Gestational Diabetes: Increased renal blood flow decreases the renal threshold, thus eliminating more sugar in the urine. Most women are tested for with a blood glucose test, between their 24th and 28th weeks of pregnancy.
• Hyperthyroidism: Increased thyroid hormones in the bloodstream can result in poor absorption of glucose from the filtrate, and glucose passes out of the body.
• High-sugar diet: High sugar content in the blood can result in exceeding the renal threshold levels of reabsorption and more sugar in the urine. The condition is called alimentary glycosuria.

• Drugs: A class of drugs that work by decreasing the absorption of sugar in the kidney and hence can induce glycosuria. These drugs work on the renal tubules and are called Dapagliflozin and canagliflozin. Their use can slightly increase the risk of urinary tract infections.(1^✔)

• Raised intracranial pressure: Hyperglycemia and glycosuria are sometimes seen in patients with increased intracranial pressure and other brain lesions. This occurs because of the activation of the sympathetic nervous system and the consequent alterations in carbohydrate metabolism.
• Liver disease: Cirrhosis of the liver affects the carbohydrate metabolism, resulting in high glucose levels in the blood. High levels of blood glucose exceed the renal threshold resulting in excretion of glucose in urine.
• Emotions causing glycosuria: Emotional glycosuria is a condition in which emotions like fear, anger, anxiety etc can cause to release the hormone adrenaline. This hormone promotes breaking down of sugars to produce energy for "flight or fight" reaction. Such an event results in temporary rise in blood sugar levels, which can exceed renal threshold for glucose resulting in glycosuria.

Other possible causes of glycosuria include:

• Post-gastrectomy
• Interstitial nephritis
• Hereditary tyrosinemia
• Glucose-galactose malabsorption in the intestine
• Wilson's disease
• Cystinosis
• Heavy metal poisoning (lead, mercury etc)

Types of Glycosuria

Based on the rate of absorption and renal threshold, benign glycosuria is categorized into three types:

Type A: Most common type of glycosuria where there is a decline in both glucose threshold and maximal glucose reabsorption rate.

Type B: The rate of reabsorption is normal but there is a decline in the renal threshold.

Type O: Glucose reabsorption does not happen in the kidneys. There is a lot of glucose excreted through urine though blood glucose, glucose tolerance and insulin levels are normal.

Symptoms of Glycosuria

Glycosuria may not present with any obvious symptoms. Pregnant women may have asymptomatic glycosuria but test positive for glucose in urine. This may not indicate any medical problems except that it could be a warning sign of gestational diabetes.

Symptoms may occur when the glycosuria is persistent and these may be subtle indicator of dehydration or the diuretic effect of the sugar. This may result in -

• Abdominal pain
• Excessive thirst
• Urinary Frequency
• Urine Urgency and sometimes leakage
• Nighttime urination or Nocturia
• Women may present with vaginal infections
• Men maybe get infections of the foreskin and glans

Other symptoms include:

• Feeling of Tiredness
• Urinary infections
• Vision trouble
• Slow healing of minor cuts or bruises
• Unexplained weight loss

If there is urinary infection it may manifest with pain in the kidney area, fever with chills and shivering and urinary frequency. Urine tests may reveal excretion of glucose along with a large number of white blood cells and protein trace.

Diagnosis of Glycosuria

Historically, glycosuria was detected by tasting the urine or with its distinctive sweet scent. Currently, urine dipstick analysis reveals the presence of excessive amounts of glucose. Further urine tests confirm the exact concentration of glucose in urine.

However it is wise to confirm this with a blood test of fasting and post prandial glucose along with HBA1C reading.

One should be warned that if using the 'stick or strip' many substances and drugs can cause a positive test without the presence of sugar in the urine and these include -

• Vitamin C ingestion
• Antibiotics like- cephalosporins and penicillins
• Parkinson's drug - Levodopa
• Blood thinners like salicylates or aspirin

There are other medications too including - Nitrofurantoin, p-aminosalicylic acid, phenazopyridine, probenecid, and X-ray contrast media.(2^✔)

Treatment of Glycosuria

The cause of glycosuria determines whether the condition is chronic or acute.

However, the presence of glucose in urine is not necessarily a serious or life-threatening condition.

Managing diabetes, Hyperthyroidism and regular kidney function tests can help in reducing excretion of sugars in urine.

There is a condition called Familial renal glycosuria (FRG). In this condition the kidney function is normal and there is persistent renal glycosuria in isolation without any kidney disorder. This is due to the mutations in the SLC5A2 gene. In this condition treatment is not typically required.(3^✔)

Prevention of Glycosuria

Reducing the amount of sugar consumption, both direct and indirect ways can help prevent high sugar levels in urine.

Glycosuria symptoms depend on glycosuria causes and may not always indicate high blood sugar levels. Renal glycosuria may show negative in blood glucose tests but positive in glucose urine.

Health Tips

• Avoid eating food that contains more sugar than necessary.
• Get regular health checks.
• During pregnancy, urinalysis must be done at frequent intervals to check gestational diabetes or glycosuria.
• Lifestyle diseases such as diabetes and obesity are factors contributing to glycosuria. Leading a healthy lifestyle and preventing such diseases can help keep glycosuria at bay.
• Home remedies like fenugreek and juice from bitter gourd have found to be helpful in controlling blood sugar and thus reducing glycosuria.

References:

1. Sodium-glucose co-transporter 2 inhibitors for type 2 diabetes mellitus: An overview for the primary care physician. - (https://www.ncbi.nlm.nih.gov/pubmed/28440009)
2. Review of drug interference with urine glucose tests. - (https://www.ncbi.nlm.nih.gov/pubmed/3552507)
3. Novel SLC5A2 mutation contributes to familial renal glucosuria: Abnormal expression in renal tissues. - (https://www.ncbi.nlm.nih.gov/pubmed/27446256)

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