What does low specific gravity of urine mean? Measuring USG is an easy and convenient way to gauge a patient’s hydration status as well as the functional ability of his kidneys. URINE SPECIFIC GRAVITY (USG) measures the concentration of particles in urine and the density of urine compared with the density of water. What does urine specific gravity tell you? High urine specific gravity can indicate that you have extra substances in your urine, such as: glucose. The higher the number, the more dehydrated you may be. Specific gravity results above 1.010 can indicate mild dehydration. What happens if specific gravity of urine is high? 10 What is the normal range of specific gravity?.8 What causes low specific gravity in urine?.5 What does it mean when specific gravity is abnormal?.3 What does a specific gravity of 1.050 mean?.2 What does urine specific gravity tell you?.1 What happens if specific gravity of urine is high?. In addition, urinary constituents (erythrocytes, leukocytes and casts) can lyse in dilute urine (USG 1. Parameters also is influenced by the specific gravity of the specimen. The interpretation of several urine chemical The USG is very useful for identifying the cause of azotemia. Knowledge of urinary solute concentration is essential for proper interpretation of BUN and serumĬreatinine, which are indicators of glomerular filtration rate. Urine osmolality can be approximated from the USG, by multiplying the last 2 digits of the USG by 36. Osmolality can be measured by freezing point depression (technique used at Cornell University) and changes in vapor pressure. Urine osmolality is directly related to the number of particles in solution and is unaffected by molecular weight and size. The following substances will increase the USG by 0.001 units. The presence of large amounts of protein and glucose will alter the USG and should be considered when interpreting USG results. It is also affected by temperature, with urine density decreasing with increasing temperatures. The USG is influenced by the number of molecules in urine, as well as their molecular weight and size, therefore it only approximates solute concentration. For routine clinical purposes, USG isĭetermined using a refractometer (refractive index generally correlates well with USG). Urine specific gravity is a measurement of the density of urine compared to pure water. When this NaCl-rich fluid enters the NaCl-permeable (water-impermeable) thin ascending limb, NaCl is absorbed passively along its concentration gradient, producing a relatively dilute renal tubule fluid.Īdapted from: Schrier: Renal and Electrolyte Disorders. This high concentration of urea osmotically extracts water from the solute-impermeable descending limb, thus concentrating NaCl in the descending-limb fluid.ĥ. In the inner medulla, water and urea are absorbed (under the action of ADH) from the collecting duct, contributing substantially to the medullary interstitial osmotic gradient.Ĥ. Water is resorbed down the osmotic gradient established in the outer medulla in the last part of the distal tubule and collecting ducts (the latter under the influence of ADH).ģ. Urea is poorly absorbed and is retained in the tubular fluid.Ģ. In the water-impermeable thick ascending limb, absorption of NaCl via the NaK2Cl carrier renders the tubular fluid dilute and the outer medullary interstitium hyperosmotic. The thin ascending limb in the inner medulla and the thick ascending limb in the outer medulla and first part of the distal tubule are permeable to NaCl but impermeable to water (as indicated by the thickened lining).ġ. Schematic representation of the passive urinary concentrating mechanism The diagram and notes below detail how the kidney concentrates urine. Urine specific gravity (USG) and osmolality are measures of the solute concentration in urine and are used to assess the ability of the renal tubules to concentrate or dilute the glomerular filtrate. Specific Gravity of Urine Specific Gravity of Urine
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