Isosthenuria refers to the excretion of urine whose

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

(concentration) is neither greater (more concentrated) nor less (more diluted) than that of protein-free plasma, typically 1.008-1.012. Isosthenuria reflects damage to the kidney's tubules or the

renal medulla The renal medulla is the innermost part of the kidney. The renal medulla is split up into a number of sections, known as the renal pyramids. Blood enters into the kidney via the renal artery, which then splits up to form the segmental arteries whi ...

. A closely related term is hyposthenuria, where the urine has a relatively low specific gravity "due to inability of the kidney to concentrate the urine normally". This specific gravity is not necessarily equal to that of plasma. Therefore, unlike isosthenuria, this condition is not associated with

kidney failure Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...

as the kidney tubules have altered the glomerular filtrate.

Clinical significance

Isosthenuria may be seen in disease states as chronic kidney disease and

acute kidney injury Acute kidney injury (AKI), previously called acute renal failure (ARF), is a sudden decrease in kidney function that develops within 7 days, as shown by an increase in serum creatinine or a decrease in urine output, or both. Causes of AKI are c ...

in which the

kidneys The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; bloo ...

lack the ability to concentrate or dilute the

urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellular ...

and so the initial filtrate of the blood remains unchanged despite the need to conserve or excrete water based on the body's hydration status.

Sickle-cell trait Sickle cell trait describes a condition in which a person has one abnormal allele of the hemoglobin beta gene (is heterozygous), but does not display the severe symptoms of sickle cell disease that occur in a person who has two copies of that all ...

, the heterozygous form of

sickle-cell disease Sickle cell disease (SCD) is a group of blood disorders typically inherited from a person's parents. The most common type is known as sickle cell anaemia. It results in an abnormality in the oxygen-carrying protein haemoglobin found in red blo ...

, presents with a normal hematological picture but is associated with hyposthenuria.Gupta AK, Kirchner KA, Nicholson R, ''et al.'' Effects of alpha-thalassemia and sickle polymerization tendency on the urine-concentrating defect of individuals with sickle cell trait and increased frequency of

urinary tract infection A urinary tract infection (UTI) is an infection that affects part of the urinary tract. When it affects the lower urinary tract it is known as a bladder infection (cystitis) and when it affects the upper urinary tract it is known as a kidne ...

s J. Clin. Invest. Vol 88, Issue 6, pgs 1963-8. Dec 1991. PMC = 295777. DOI = 10.1172/JCI115521

References

Abnormal clinical and laboratory findings for urine {{Med-sign-stub

Clinical significance

See also

References