The presence of sugar in urine, known as glycosuria, indicates that glucose is being excreted through the kidneys. Its appearance in urine is typically an unusual finding. Normally, kidneys efficiently prevent glucose loss. If sugar is detected, it may signal an underlying health condition, prompting further investigation.
How the Body Manages Sugar
The body meticulously regulates glucose after carbohydrates are digested into glucose, which then enters the bloodstream. The pancreas responds to rising blood glucose levels by releasing insulin. Insulin enables glucose to move from the bloodstream into cells for energy. Insulin also prompts the liver to store excess glucose as glycogen for future energy needs.
The kidneys play a role in maintaining this delicate balance. Blood is filtered through tiny structures called glomeruli. During filtration, glucose enters the kidney tubules. Specialized transport proteins in the proximal tubules reabsorb almost all filtered glucose back into the bloodstream.
This reabsorption capacity is not limitless. The point at which the kidneys can no longer reabsorb all filtered glucose is the “renal threshold” for glucose. If blood glucose levels exceed this threshold, typically around 180 to 200 milligrams per deciliter (mg/dL), the excess glucose spills into the urine. Its presence in urine indicates that blood glucose levels have surpassed the kidneys’ ability to reclaim it.
Reasons for Sugar in Urine
The most frequent reason for glucose to appear in urine is elevated blood sugar levels, often associated with diabetes mellitus. In Type 1 diabetes, the pancreas does not produce enough insulin, while in Type 2 diabetes, the body either does not produce sufficient insulin or does not utilize it effectively. In both cases, high blood glucose concentrations overwhelm the kidneys’ reabsorption capacity, leading to excretion in the urine.
Another cause is renal glycosuria, a condition where the kidneys themselves have a lower-than-normal renal threshold for glucose. This means glucose can appear in the urine even when blood sugar levels are within a normal range. This condition often results from genetic variations affecting the kidney tubules’ ability to reabsorb glucose. Medical evaluation is important to rule out other factors.
Pregnancy can also lead to the presence of sugar in urine. During pregnancy, some individuals experience a temporary lowering of their renal threshold for glucose. This can also be a sign of gestational diabetes, a form of diabetes that develops during pregnancy.
Certain medications are designed to cause glucose to be excreted in the urine. A class of drugs called SGLT2 inhibitors, or “gliflozins,” specifically block the reabsorption of glucose in the kidneys. This helps lower blood glucose levels in individuals with diabetes. Rare genetic conditions like Fanconi syndrome can also affect kidney reabsorption of various substances, including glucose, leading to its presence in urine. A temporary form, alimentary glycosuria, can also occur after consuming large carbohydrates.
Understanding Your Diagnosis
Detecting sugar in urine warrants consultation with a healthcare professional to determine the cause. While a urine test can indicate the presence of glucose, it is not as accurate as blood tests for diagnosing conditions like diabetes. Urine tests are often part of a broader health assessment.
Several blood tests identify the reason for glycosuria. A fasting blood glucose test measures blood sugar levels after an 8- to 12-hour fast and is frequently used for initial screening. An oral glucose tolerance test (OGTT) measures blood glucose before and at specific intervals after consuming a sugary drink, providing insight into sugar processing. This test is useful for diagnosing diabetes, including gestational diabetes.
The HbA1c test provides an average of blood glucose levels over two to three months. It measures the percentage of hemoglobin with attached glucose and does not require fasting. Early diagnosis and management of the condition causing sugar in urine are important for health and preventing complications.