The specific weight of the urine depends on the quantity of substances dissolved in them; among these, the main contribution is provided by urea, nitrogen, sodium chloride and various minerals, as well as "anomalous" substances such as glucose and proteins. Therefore, the more concentrated the urine, the greater their specific weight; if we drink a lot, for example, the urinary volume increases and the specific weight decreases; vice versa, in conditions of marked dehydration the urine is more concentrated and the specific weight is higher.
Urine specific gravity High = HYPERSTENURIA
Increased urine specific gravity is common to all conditions characterized by dehydration, such as diarrhea, vomiting, excessive sweating, and glucosuria (presence of glucose in the urine).
A high urinary specific weight is also a consequence of kidney diseases that decrease the organ's ability to reabsorb an "abnormal" filtrate. If we compare our kidneys to sieves, in some conditions it can happen that the meshes loosen, letting substances pass normally. considered as proteins, this is the case of nephrotic syndrome. Among the other kidney diseases responsible for hyperstenuria we remember the stenosis of the renal artery (which decreases the blood supply to the kidneys) and the hepatorenal syndrome.
A rare disease that increases the specific gravity of urine is the so-called syndrome of inappropriate (excessive) secretion of antidiuretic hormone (ADH or vasopressin; as the name suggests, this "hormone promotes the reabsorption of water in the renal tubules by acting on the dehydration) In congestive heart failure, the specific gravity of the urine increases due to the reduced blood supply to the kidney.
Low urine specific gravity = HYPOSTENURIA
The decrease in the specific gravity of the urine is often the result of excessive dilution of the same, as occurs in diuretic therapy, in both pituitary (in which the production of ADH is lacking) and nephrogen (in which the kidney is insensitive to ADH), in the reabsorption of edema or more simply in the excessive intake of liquids. A low specific gravity of urine is also a consequence of kidney diseases that decrease the organ's ability to concentrate or dilute urine, as occurs in chronic renal failure, tubular necrosis, interstitial nephritis and acute pyelonephritis (kidney infections) .
In chronic renal insufficiency, the specific weight of the urine tends to remain almost constant over time (1007 - 1010 g / L), regardless of the state of hydration of the organism; in these cases we speak of isostenuria to emphasize the emission of urine with constant specific weight, even after water restriction or the introduction of large quantities of water.
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