Normal urine contains no glucose because the kidneys are able to reclaim all of the filtered glucose back into the bloodstream.
What does glucose in urine mean?
'Glucose in urine' is glycosuria or glucosuria, and refers to the excretion of glucose into the urine.
What are the causes of glucose present in urine?
Glycosuria can be due to:
1. Diabetes mellitus (most common)
2. Intrinsic problem with glucose reabsorption in kidneys (rare)
Glycosuria is nearly always caused by elevated blood glucose levels, most commonly due to untreated diabetes mellitus. Excess glucose in the blood spills over and exits in urine.
Rarely, glycosuria is due to an intrinsic problem with glucose reabsorption within the kidneys themselves, a condition termed renal glycosuria.
What causes osmotic diuresis?
Glucose is an osmotic molecule - it attracts water. Glycosuria leads to excessive water loss into the urine with resultant dehydration, a process called osmotic diuresis.
Explain the filtration of glucose in the kidney.
Blood is filtered by millions of nephrons, the functional units that comprise the kidneys. In each nephron, blood flows from the arteriole into the glomerulus, a tuft of leaky capillaries. The Bowman's capsule surrounds each glomerulus, and collects the filtrate that the glomerulus forms.
The filtrate contains waste products (e.g. urea), electrolytes (e.g. sodium, potassium, chloride), amino acids, and glucose.
Explain the reabsorption of glucose in the kidney.
The filtrate passes into the renal tubules of the kidney. In the first part of the renal tubule, the proximal tubule, glucose is reabsorbed from the filtrate, across the tubular epithelium and into the bloodstream.
The proximal tubule can only reabsorb a limited amount of glucose. When the blood glucose level exceeds about 8.9-10.0 mmol/L (160 – 180 mg/dL), the proximal tubule becomes overwhelmed and begins to excrete glucose in the urine.
What happens when blood glucose exceeds the renal threshold for glucose?
Glucose will be excreted into urine; glucose appears in urine; glucose can be detected in urine.
What is the renal threshold of glucose?
The point at which high glucose exceeds the renal threshold of glucose (RTG) causes it to overflow into urine.
The average renal threshold of glucose is 8.9-10.0 mmol/L (160-180 mg/dL).
It varies in individuals and in different physiological states; it is lowered in pregnancy and in children.
What is the renal threshold for glucose in children and pregnant women?
Children and pregnant women, may have a low RTG (less than ~7 mmol/L or 126 mg/dL glucose in blood to have glucosuria).
What are the other conditions where glucosuria may occur?
Glucosuria can occur temporarily from:
- emotional stress or pain,
- hyperthyroidism,
- alimentary hyperglycemia, and
- meningitis.
What is renal glycosuria?
If the RTG is so low that even normal blood glucose levels produce the condition, it is referred to as renal glycosuria.
What is the urine dipstick test?
The urine dipstick test is a convenient urine test where a reagent test strip is used and dipped in freshly voided urine for the detection of pH, specific gravity (S.G.), protein, ketone, glucose, hemoglobin, red blood cells (rbc), white blood cells (wbc), and others.
Different dipsticks test for different things or combinations in urine.
The urine dipstick test is often used for OSCEs, a type of practical examination format that is used in medical schools.
What is the relationship between glucose detected by dipstick and blood/plasma glucose levels?
External links:
http://wiki.answers.com/Q/How_do_you_lower_blood_glucose#slide=4
http://www.elmhurst.edu/~chm/vchembook/624diabetes.html
http://en.wikipedia.org/wiki/Glycosuria
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