Glycosuria
Encyclopedia
Glycosuria or glucosuria is the excretion of glucose
into the urine. Ordinarily, urine contains no glucose because the kidneys are able to reclaim all of the filtered glucose back into the bloodstream. Glycosuria is nearly always caused by elevated blood glucose levels, most commonly due to untreated diabetes mellitus
. Rarely, glycosuria is due to an intrinsic problem with glucose reabsorption within the kidneys themselves, a condition termed renal glycosuria
. Glycosuria leads to excessive water loss into the urine with resultant dehydration, a process called osmotic diuresis
.
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. 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 160 – 180 mg/dl, the proximal tubule becomes overwhelmed and begins to excrete glucose in the urine.
This point is called the renal threshold of glucose (RTG). Some people, especially children and pregnant women, may have a low RTG (less than ~7 mmol/L glucose in blood to have glucosuria).
If the RTG is so low that even normal blood glucose levels produce the condition, it is referred to as renal glycosuria
.
Glucose in urine can be identified by Benedict's qualitative test.
A urine dipstick can show a false-positive glucosuria if someone is taking Pyridium or AZO Standard, medications that relieve symptoms of urinary tract infection.
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
into the urine. Ordinarily, urine contains no glucose because the kidneys are able to reclaim all of the filtered glucose back into the bloodstream. Glycosuria is nearly always caused by elevated blood glucose levels, most commonly due to untreated diabetes mellitus
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
. Rarely, glycosuria is due to an intrinsic problem with glucose reabsorption within the kidneys themselves, a condition termed renal glycosuria
Renal glycosuria
Renal glycosuria, also known as renal glucosuria, is a rare condition in which the simple sugar glucose is excreted in the urine despite normal or low blood glucose levels. With normal kidney function, glucose is excreted in the urine only when there are abnormally elevated levels of glucose in...
. Glycosuria leads to excessive water loss into the urine with resultant dehydration, a process called osmotic diuresis
Osmotic diuresis
Osmotic diuresis is increased urination caused by the presence of certain substances in the small tubes of the kidneys. The excretion occurs when substances such as glucose enter the kidney tubules and cannot be reabsorbed...
.
Pathophysiology
Blood is filtered by millions of nephrons, the functional units that comprise the kidneys. In each nephron, blood flows from the arterioleArteriole
An arteriole is a small diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries.Arterioles have muscular walls and are the primary site of vascular resistance...
into the glomerulus
Glomerulus
A glomerulus is a capillary tuft that is involved in the first step of filtering blood to form urine.A glomerulus is surrounded by Bowman's capsule, the beginning component of nephrons in the vertebrate kidney. A glomerulus receives its blood supply from an afferent arteriole of the renal...
, a tuft of leaky capillaries. The Bowman's capsule
Bowman's capsule
The Bowman's capsule is a cup-like sac at the beginning of the tubular component of a nephron in the mammalian kidney that performs the first step in the filtration of blood to form urine. A glomerulus is enclosed in the sac...
surrounds each glomerulus, and collects the filtrate that the glomerulus forms. The filtrate contains waste products (e.g. urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
), electrolytes (e.g. sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
, potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
, chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
), amino acids, and glucose. The filtrate passes into the renal tubules of the kidney. In the first part of the renal tubule, the proximal tubule
Proximal tubule
The proximal tubule is the portion of the duct system of the nephron of the kidney which leads from Bowman's capsule to the loop of Henle.-Structure and appearance:...
, 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 160 – 180 mg/dl, the proximal tubule becomes overwhelmed and begins to excrete glucose in the urine.
| Urine dipstick Urinalysis A urinalysis , also known as Routine and Microscopy , is an array of tests performed on urine, and one of the most common methods of medical diagnosis... designation | Approximate plasma Blood plasma Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid... concentration |
|---|---|
| trace | 100 mg/dL |
| 1+ | 250 mg/dL |
| 2+ | 500 mg/dL |
| 3+ | 1000 mg/dL |
| 4+ | 2000 mg/dL |
This point is called the renal threshold of glucose (RTG). Some people, especially children and pregnant women, may have a low RTG (less than ~7 mmol/L glucose in blood to have glucosuria).
If the RTG is so low that even normal blood glucose levels produce the condition, it is referred to as renal glycosuria
Renal glycosuria
Renal glycosuria, also known as renal glucosuria, is a rare condition in which the simple sugar glucose is excreted in the urine despite normal or low blood glucose levels. With normal kidney function, glucose is excreted in the urine only when there are abnormally elevated levels of glucose in...
.
Glucose in urine can be identified by Benedict's qualitative test.
A urine dipstick can show a false-positive glucosuria if someone is taking Pyridium or AZO Standard, medications that relieve symptoms of urinary tract infection.