Urine Specific Gravity
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Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. Urine Specific Gravity Urine Specific Gravity (SG) Specific gravity (SG) is a measurement of the kidneys' ability to concentrate urine. The test compares the density of urine against the density of distilled water, which has an SG of 1.000. Because urine is a solution of minerals, salts, and compounds dissolved in water, the SG is a measure of the density of the dissolved chemicals in the specimen. As a measurement of specimen density, SG is influenced by both the number of particles present and the size of the particles. Osmolality is a more exact measurement and may be needed in certain circumstances. Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • The range of urine SG depends on the state of hydration and varies with urine volume and the load of solids to be excreted under standardized conditions; when fluid intake is restricted or increased, SG measures the concentrating and diluting functions of the kidney. Loss of these functions is an indication of renal dysfunction. Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Reference Values • Normal • 1.005-1.030 (usually between 1.010 and 1.025) • Concentrated urine: 1.025-1.030+ • Dilute urine: 1.001-1.010 • Infant < 2 years old: 1.001-1.018 Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Procedure • Test SG with the use of a multiple-test dipstick that has a separate reagent area for SG. An indicator changes color in relation to ionic concentration, and this result is translated into a value for SG. • Determine SG with a refractometer or total solids meter. The refractive index is the ratio of the velocity of light in air to the velocity of light in the test solution. A drop of urine is placed on a clear glass plate of the urinometer and another plate is pressed on top of the urine sample. The path of light is deviated when it enters the solution, and the degree of deviation (refraction) is directly proportional to the density of the solution. • The urinometer (hydrometer) is the least accurate method. It consists of a bulb-shaped instrument that contains a scale calibrated in SG readings. Urine (10–20 mL) is transferred into a small test tube“like cylinder, and the urinometer is floated in the urine. The SG is read off the urinometer at the meniscus level of the urine. This method is becoming obsolete owing to the ease of dipstick testing. Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Specimen collection – For regular UA testing, about 20 mL of a random sample is needed for testing (UA including SG). – When a special evaluation of SG is ordered separately from the UA, the patient should fast for 12 hours before specimen collection. • Clinical Implications • Normal SG: SG values usually vary inversely with the amount of urine excreted (decreased urine volume = increased SG). However, this relationship is not valid in certain conditions, including: – Diabetes(increased urine volume, increased SG) – Hypertension(normal volume, decreased SG) – Early chronic renal disease in which there is increased volume, decreased SG Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Hyposthenuria (low SG, 1.001-1.010) occurs in the following conditions: – Diabetes insipidus (low SG with large urine volume). It is caused by absence or decrease of ADH, a hormone that triggers kidney absorption of water. Without ADH, the kidneys produce excessive amounts of urine that are not reabsorbed (sometimes 15-20 L/day). – Glomerulonephritis (kidney inflammation without infection) and phelonephritis (kidney inflammation with bacterial infection, but not in the acute type of this disease). SG can be low in glomerulonephritis, with decreased urine volume. Tubular damage affects the kidneys' ability to concentrate urine. – Severe renal damage with disturbance of both concentrating and diluting abilities of urine. The SG is low (1.010) and fixed (varying little from specimen to specimen); this is termed isosthenuria. Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Hypersthenuria (increased SG, 1.025-1.035) occurs in the following conditions: – Diabetes mellitus – Nephrosis – Excessive water loss (dehydration, fever, vomiting, diarrhea) – Increased secretion of ADH and diuretic effects related to the stress of a surgical procedure – Congestive heart failure – Toxemia of pregnancy Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Interfering Factors • Radiopaque x-ray contrast media, minerals, and dextran may cause falsely high SG readings on the refractometer. The reagent dipstick method is not affected by high- molecular-weight substances. • Temperature of urine specimens affects SG; cold specimens produce falsely high values using the hydrometer. • Highly buffered alkaline urine may also cause low readings (with dipsticks only). • Elevated readings may occur in the presence of moderate amounts of protein (100–750 mg/dl) or with patients receiving intravenous albumin. • Detergent residue (on specimen containers) can produce elevated SG results. • Diuretics and antibiotics cause high readings. • drugs may affect test outcomes Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Intervention • Pretest Patient Preparation • Explain the purpose and procedure for urine collection. • Follow guidelines for safe, effective, informed pretest care. • Posttest Patient Aftercare • Interpret test outcomes, counsel, and monitor appropriately for conditions associated with altered SG. • Follow guidelines for safe, effective, informed posttest care Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. 2. Urine Osmolality • Osmolality, a more exact measurement of urine concentration than SG, depends solute in a unit of solution. More information concerning renal function can be obtained if serum and urine osmolality tests are run at the same time. The normal ratio between urine and serum osmolality is 3:1. A high urine-to- serum ratio is seen with concentrated urine. With poor concentrating ability, the ratio is low. Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • measurement is indicated to evaluate the concentrating and diluting ability of the kidney, this test is done. Urine osmolality during water restriction is an accurate test of decreased kidney function. It is also used to monitor the course of renal disease; to monitor fluid and electrolyte therapy; to establish the differential diagnosis of hypernatremia, hyponatremia, and polyuria; and to evaluate the renal response to ADH. Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Reference Values • Normal • 24-hour specimen: 300-900 mOsm/kg of H2O • Random specimen: 50-1200 mOsm/kg of H2O • Urine-to-serum ratio: 1:1 to 3:1 • Procedure 1. Tell patient that this is a 24-hour urine collection test. 2. For the 24-hour test, the patient voids at approximately 7:00 a.m. (0700). All of the urine voided is saved in a special 24-hour collection container kept on ice or refrigerated. A high-protein diet may be ordered. At the end of the test, the specimen is labeled and sent to the laboratory. 3. Simultaneous determination of serum osmolality may be done. A high urine-to- serum ratio is seen with concentrated urine Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Clinical Implications • Osmolality is increased in: – Prerenal azotemia – Congestive heart failure – Addison's disease – Syndrome of inappropriate ADH secretion (SIADH) – Dehydration – Amyloidosis – Hyponatremia • Osmolality is decreased in: – Acute renal failure – Diabetes insipidus – Hypokalemia – Hypernatremia – Primary polydipsia – Hypercalcemia – Compulsive water drinking (increased fluid intake) Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Urine-to-serum ratio is: – Increased in prerenal azotemia – Decreased in acute tubular necrosis • Interfering Factors • Intravenous sodium administration • Intravenous dextrose and water administration • Interventions • Pretest Patient Preparation • Explain purpose and procedure of the test to the patient. • A normal diet is prescribed for 3 days before testing. • To increase sensitivity of the osmolality test, a high-protein diet may be ordered for 3 days before the test. No liquids with the evening meal and no food or liquids should be taken after the evening meal until patient has diabetes. • Follow guidelines for safe, effective, informed pretest care. Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. • Posttest Patient Aftercare • Provide the patient with foods and fluids as soon as the last urine sample is obtained. • Interpret test outcomes and monitor appropriately. • Follow guidelines for safe, effective, posttest care. Please purchase PDFcamp Printer on http://www.verypdf.com/ to remove this watermark. Urine pH • The symbol pH expresses the urine as a dilute acid or base solution and measures the free hydrogen ion (H+) concentration in the urine; 7.0 is the point of neutrality on the pH scale. The lower the pH, the greater the acidity; the higher the pH, the greater the alkalinity. The pH is an indicator of the renal tubules' ability to maintain normal hydrogen