Decreased urine specific gravity

Introduction Urine specific gravity refers to the ratio of the weight of the same volume of water at 4 degrees Celsius. It is an indicator of the concentration of solute contained in urine. Urine specific gravity is mainly used to understand the function of enrichment and dilution of the kidney, and can also be used for the auxiliary diagnosis and condition monitoring of certain diseases. The urine specific gravity of normal people may fluctuate greatly depending on the situation of diet and drinking water, sweating and urination. The baby's urine specific gravity is much lower than that of adults. The 24-hour urine specific gravity of healthy people is between 1.010 and 1.025. The specific gravity of the urine is related to the amount of water and the urine value at that time, mainly depending on the concentration function of the kidney.

Cause

Reduced: seen in diabetes insipidus, chronic nephritis.

Urinary specific gravity <1.010 is hypotonic urine, seen in impaired renal concentrating function, such as chronic glomerulonephritis, acute nephritis, polyuria, uremia and polyuria. Specific gravity can be used as a reference for the identification of diabetes and diabetes insipidus. The former has a large amount of urine and a high proportion. The latter has a large amount of urine and a low specific gravity.

Urine specific gravity is mainly used to understand the function of enrichment and dilution of the kidney, and can also be used for the auxiliary diagnosis and condition monitoring of certain diseases. The urine specific gravity of normal people may fluctuate greatly depending on the situation of diet and drinking water, sweating and urination. The baby's urine specific gravity is much lower than that of adults. The 24-hour urine specific gravity of healthy people is between 1.010 and 1.025.

an examination

Related inspection

Urine routine water test

First, urine routine: urine specific gravity is low, mostly below 1.020, often fixed at 1.010 in the late stage of the disease. Urinary protein traces ~+++. There are often red blood cells and casts in the urine (granular tube type, transparent tube type). There is obvious hematuria or gross hematuria during the acute attack.

Second, blood test: often have mild to moderate pigmented anemia, red blood cells and hemoglobin proportion decreased, erythrocyte sedimentation rate increased, may have hypoproteinemia, general serum electrolytes no obvious abnormalities.

Third, renal function test: glomerular filtration rate, endogenous creatinine clearance rate decreased, blood urea nitrogen and creatinine increased, renal function staging mostly compensated or decompensated period, phenol red excretion test and urine concentration dilution The function is reduced.

Water test

Urine specific gravity inspection method:

1. Test strip method: also known as dry chemical method, there are instrument colorimetry and visual colorimetry. The test strip contains an acid-base indicator and a polyelectrolyte.

2. Refractometer method: There is a trial clinical refractometer method and a portable refractometer method. The measurement is made using the correlation between the refractive index of light and the total amount of solids in the solution.

3. Urine hydrometer method: The ratio of the weight of urine to the same volume of water at 4 degrees Celsius is measured by a special hydrometer.

4. Weighing method: At the same temperature, weigh the same volume of urine and water separately, and compare them to obtain the specific gravity of urine.

Differential diagnosis

Differential diagnosis

Increased urine specific gravity: Urine specific gravity measurement is used to estimate the concentrating function of the kidney, but the accuracy is poor and the affected factors are many. The measured values are for reference only. Increased urine specific gravity is seen in dehydration, diabetes, acute nephritis and so on. The proteinuria is light and heavy (1~3g/d). There are microscopic hematuria. The red blood cells are pleomorphic and diverse. Sometimes, red blood cell casts, granular casts and renal tubular epithelial cells can be seen. Urinary fibrin degradation products (FDP) can be positive. Blood urea nitrogen and creatinine may increase transiently, serum total complement (CH50) and C3 decrease, return to normal within more than 8 weeks, and serum anti-streptolysin "O" titer may increase.

Increased urinary biliary: urinary biliary is derived from the binding of bilirubin. In combination with bilirubin in the lower part of the small intestine and in the colon, it is decoupled by the action of intestinal bacteria. After several stages of reduction, bilirubin becomes urinary biliary and then excreted with feces. A part of urinary biliary is absorbed into the portal vein from the intestine, most of which is taken up by the liver cells and then discharged into the intestinal fluid (intestinal hepatic circulation), and part of it enters the systemic circulation from the portal vein and is excreted from the urine through the kidney. A variety of factors can cause an increase in urinary biliary.

Increased urinary amylase: When pancreatitis and other diseases occur, pancreatic amylase enters the bloodstream and is excreted from the urine due to inflammation and other diseases in the pancreatic tissue, causing the patient's blood amylase to rise and amylase to be detected in the urine. Amylase assay, which is one of the important objective indicators for the diagnosis of acute pancreatitis, but not a specific diagnostic method. In the early stage of the disease, when there is embolism of the pancreatic blood vessels and some hemorrhagic necrotizing pancreatitis, it may not increase due to severe destruction of pancreatic tissue. Amylase may also increase in the case of shock, acute renal failure, pneumonia, mumps, perforation of ulcer disease, and intestinal and biliary infections. Therefore, when there is an increase in amylase, it is necessary to combine the history, symptoms and signs to rule out the increase of amylase caused by non-pancreatic diseases, in order to diagnose acute pancreatitis.

Urine osmotic pressure decreased: Urine osmotic pressure, also known as urinary osmolality, is the number of particles that reflect solute molecules and ions per unit volume of urine. The decrease in osmolality reflects the decrease in the concentration of the distal tubules, as seen in chronic pyelonephritis, chronic interstitial lesions caused by various causes, and chronic renal failure.

The urinary filtration fraction is significantly reduced: the production of urine depends on the filtration of the glomerulus and the reabsorption and secretion of the renal tubules and collecting ducts. Therefore, the regulation of the body's formation of urine is achieved by adjusting the filtration, reabsorption and secretion. The amount of filtrate produced by the two kidneys per unit time is called glomerular filtration rate (GFR), which is about 125 ml/min in normal adults. The ratio of glomerular filtration rate to renal plasma flow is called the filtration fraction. The renal plasma flow rate per minute is about 660 ml, so the filtration fraction is 125/660 x 100% 19%. This result indicates that about one-fifth of the plasma flowing through the kidney is filtered into the sac by the glomerulus to produce primary urine. Glomerular filtration rate and filtration fraction are indicators of renal function. Glomerular capillary blood pressure is significantly reduced, renal vasoconstriction, filtration membrane permeability and changes in filtration area can reduce glomerular filtration rate.

The material in this site is intended to be of general informational use and is not intended to constitute medical advice, probable diagnosis, or recommended treatments.