![]() ![]() Normally, only small plasma proteins filtered at theglomerulus are reabsorbed by the renal tubule. Proteinĭipstick screening for protein is done on whole urine, but semi-quantitativetests for urine protein should be performed on the supernatant of centrifugedurine since the cells suspended in normal urine can produce a falsely highestimation of protein. Subtract 0.004 for every 1% glucose to determine non-glucose solute concentration. In end-stage renal disease,sp gr tends to become 1.007 to 1.010.Īny urine having a specific gravity over 1.035 is either contaminated,contains very high levels of glucose, or the patient may have recently receivedhigh density radiopaque dyes intravenously for radiographic studies or low molecular weight dextran solutions. If sp gr is not > 1.022 after a 12 hour period without food or water,renal concentrating ability is impaired and the patient either has generalizedrenal impairment or nephrogenic diabetes insipidus. Since the sp gr of theglomerular filtrate in Bowman's space ranges from 1.007 to 1.010, anymeasurement below this range indicates hydration and any measurement above itindicates relative dehydration. Specific gravity between 1.002 and 1.035 on a random sample should beconsidered normal if kidney function is normal. The ability of the kidneys to concentrate or dilute the urine over that of plasma is being measured. A U-Osm of 400 mOsm/Kg equates to sp gr of 1.010, and 800 mOsm/kg to sp gr of 1.020 (Note: the amount of solute in a kilogram of solvent is termed osmolality, and the amount per liter of solvent is osmolarity). Urine specific gravity (U-SG) is directly proportional to urine osmolality (U-Osm). Therefore, dipstick specific gravity is altered by very high or low urine pH, but not large particles like proteins. The urine dipstick measurement of specific gravity is an approximation that is most sensitive to cationic concentration in urine. Larger particles such as glucose and albumin will alter refraction to a greater degree. A refractometer measures the change in direction of a light path (refraction) based upon particle concentration and size in a fluid. The most common method of measurement is freezing point depression. Urine osmolality measures the total number of dissolved particles, regardless of their size. Specific gravity of urine is determined by the presence of solutes represented by particles of varying sizes, from small ions to larger proteins. The change to the acid side of 7.4 is accomplished in the distalconvoluted tubule and the collecting duct. However,depending on the acid-base status, urinary pH may range from as low as 4.5 to ashigh as 8.0. The glomerular filtrate of blood plasma is usually acidified by renal tubulesand collecting ducts from a pH of 7.4 to about 6 in the final urine. The strip is dipped into the urine sample, and after the appropriate number of seconds, the color change is compared to a standard chart to determine the findings. If the samplecontained many red blood cells, it would be cloudy as well as red.Įxamples of appearances of urine URINE DIPSTICK CHEMICAL ANALYSIS OverviewĪ dipstick is a paper strip with patches impregnated with chemicals that undergo a color change when certain constituents of the urine are present or in a certain concentration. Clearing of thespecimen after addition of a small amount of acid indicates that precipitationof salts is the probable cause of tubidity.Ī red or red-brown (abnormal) color could be from a food dye, eating freshbeets, a drug, or the presence of either hemoglobin or myoglobin. ![]() Turbidity or cloudiness may be caused by excessive cellular material orprotein in the urine or may develop from crystallization or precipitation ofsalts upon standing at room temperature or in the refrigerator. Normal urine volumeis 750 to 2000 ml/24hr. Normal, freshurine is pale to dark yellow or amber in color and clear. The first part of a urinalysis is direct visual observation. Microscopic urinalysis requires only a relatively inexpensive lightmicroscope. However, a careless doctor,nurse, or assistant is entirely capable of misreading or misinterpreting theresults. The color change occurring on each segment of the stripis compared to a color chart to obtain results. This microchemistry system has been available for many years andallows qualitative and semi-quantitative analysis within one minute by simplebut careful observation. The most cost-effective device used to screen urine is a paper or plasticdipstick. Examples include diabetes mellitus, variousforms of glomerulonephritis, and chronic urinary tract infections. Urinalysis can reveal diseases that have gone unnoticed because they do notproduce striking signs or symptoms. ![]()
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