Chemical Examination of Urine

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1

reagent strips

the most common method for chemical testing

2

ascorbic acid

high amounts that can interfere and cause false positives

3

moisture, heat, chemicals, and light

factors that reagent strips should be protected against

4

isothenuria

specific gravity of urine will always be 1.010; implies end stage renal disease; tubules of nephron are unable to function properly

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1.002-1.035

normal specific gravity

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specific gravity strip method

measures ionic solutes Na K Cl NH4

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polyelectrolyte and a pH indicator

impregnated into reagent strip pad at alkaline pH that allows for the color change when protons are released decreasing pH

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bromthymol blue

indicator of color change

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4.5-8.0

normal pH of urine

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bromothymoml blue and and methyl red

double indicators of pH test pad

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5.0

pH orange

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7.0

pH green

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9.0

pH blue

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4.5 or less, 8.0 or more

not physiologically possible pH

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yellow green

pH urine turns blue green to?

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???

three most common reasons for a urine pH to be above 8.0

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proteins

normally very small amounts in urine

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150 mg

normal amount of protein in urine

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proteinuria

first sign of kidney disease

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albumin

the protein usually present at increased concentration; strip test most sensitive

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prerenal

overflow proteinuria; too much protein in plasma and passes into urine; septicemia, hemoglobinuria, and myoglobinuria, MM BJ proteins

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renal

glomerular and tubular proteinuria; GFB is defective allowing proteins in plasma to enter ultra filtrate; tubular reabsorption function is altered or impaired

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postrenal

develops from inflammatory process in the urinary tract

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nephrotic syndrome

most serious and damaging type of glomerular proteinuria, renal

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fanconi's

proximal tubular dysfunction; renal proteinuria

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sulfosalicylic acid precipitation test

detects all proteins in urine albumin and globulins; historical

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reagent strip tests

protein error in indicators; buffers hole pH constant indicator dyes release H ions due to proteins present; H and proteins create color change; blue green

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greater than 9.0 pH

can produce false positive proteins

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hematuria

red blood cells in urine; smoky, cloudy urine clarity

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hemoglobinuria

free hemoglobin in urine; clear urine clarity

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myoglobin

intracellular protein of muscle that will e increased in the bloodstream when muscle tissue is damaged by trauma or disease and will pass through glomerular filtration barrier; detected in reagent strip; also caused by alcohol OD, toxins (cocaine or heroin) and certain metabolic disorders

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hemoglobinuria

red or brown urine; plasma shows hemolysis

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myoglobinuria

pink, red or brown urine; plasma appears normal

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ammonium sulfate precipitation method

historical method to differentiate hemoglobinuria from myoglobinuria

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heme's pseudoperoxidase activity

pad contains chromogen and peroxide to detect blood; heme reduces peroxide, chromogen is oxidized, causing color change from yellow to green

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ascorbic acid (vitamin C)

interferes with hydrogen peroxide in blood and glucose, bilirubin, and nitrites reactions causing false negative suggested by microscopic findings but negative reagent strip result

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leukocyte esterase

normally few WBCs seen

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greater than 20 u/L

a leukocyte indication of pathologic process (inflammation) from kidney (pyelonephritis) to urinary tract (urethritis)

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leukocyte esterase

azurophilic granules of leukocytes to cleave an ester in pad; cleavage forms and couples with diazonium salt; end result is azo dye and color change from beige to violet

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lymphocytes

not detected in leukocyte esterase strip pad

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10-25 WBCs/uL

amount detected in leukocyte esterase

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nitrite

formed from nitrate reducing bacteria

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diazotization reaction of nitrite with aromatic amine pad

forms diazonium salt which couples with compound in pad to produce azo dye; color change white to pink

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glucosuria

presence of glucose in urine

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glycosuria

presence of non-glucose sugars (fructose sucrose lactose) or combination in urine

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glucose

not normally seen in normal urine

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diabetes mellitus

most common disease that causes hyperglycemia and glucosuria

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160-180 mg/dL

renal threshold for plasma glucose

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galactose

most significant sugar other than glucose signifying inability to metabolize it into glucose (GALT seen in infants)

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glucose oxidase

double sequential; oxidizes glucose to form hydrogen peroxide and gluconic acid; peroxidase oxidizes chromogen in pad resulting in color change; specific for glucose

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(Benedict's) copper reduction tests

used to identify reducing sugars; most common is Clinitest (tablet test); strip negative for glucose, Clintest positive, sugars present other than glucose

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ketones

breakdown products from large amounts of fatty acids

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acetoacetate

principal form detected by reagent strip method

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B-Hydroxybutyrate

not detected by strip tests

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ketonuria

caused when blood ketone level exceeds 70 mg/dL; breath fruity; caused by starvation, bulimia, strenuous exercise, diabetes mellitus, or alcoholism

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70 mg/dL

renal threshold for ketones

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nitroprusside reaction

used to detect ketones; color change from beige to purple; positives always confirmed with Acetest

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acetest

tablet test used to correctly identify ketones if truly present

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bilirubin

seen in hepatic or post hepatic jaundice

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diazo reaction

only direct conjugated bilirubin detected since indirect is not water soluble and stays bound to albumin; bilirubin reacts with diazonium salt in pad to form azobilirubin which is brown

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ictotest

tablet test for confirmation of bilirubin in urine; detects even lower amounts than strip test; azo coupling of bilirubin with diazonium salt

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urobilinogen

normally present in low amounts

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Ehrlich's reaction

multistix

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chemstrip

use azocoupling reaction specific for urobilinogen