Chemical Examination of Urine
reagent strips
the most common method for chemical testing
ascorbic acid
high amounts that can interfere and cause false positives
moisture, heat, chemicals, and light
factors that reagent strips should be protected against
isothenuria
specific gravity of urine will always be 1.010; implies end stage renal disease; tubules of nephron are unable to function properly
1.002-1.035
normal specific gravity
specific gravity strip method
measures ionic solutes Na K Cl NH4
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
bromthymol blue
indicator of color change
4.5-8.0
normal pH of urine
bromothymoml blue and and methyl red
double indicators of pH test pad
5.0
pH orange
7.0
pH green
9.0
pH blue
4.5 or less, 8.0 or more
not physiologically possible pH
yellow green
pH urine turns blue green to?
???
three most common reasons for a urine pH to be above 8.0
proteins
normally very small amounts in urine
150 mg
normal amount of protein in urine
proteinuria
first sign of kidney disease
albumin
the protein usually present at increased concentration; strip test most sensitive
prerenal
overflow proteinuria; too much protein in plasma and passes into urine; septicemia, hemoglobinuria, and myoglobinuria, MM BJ proteins
renal
glomerular and tubular proteinuria; GFB is defective allowing proteins in plasma to enter ultra filtrate; tubular reabsorption function is altered or impaired
postrenal
develops from inflammatory process in the urinary tract
nephrotic syndrome
most serious and damaging type of glomerular proteinuria, renal
fanconi's
proximal tubular dysfunction; renal proteinuria
sulfosalicylic acid precipitation test
detects all proteins in urine albumin and globulins; historical
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
greater than 9.0 pH
can produce false positive proteins
hematuria
red blood cells in urine; smoky, cloudy urine clarity
hemoglobinuria
free hemoglobin in urine; clear urine clarity
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
hemoglobinuria
red or brown urine; plasma shows hemolysis
myoglobinuria
pink, red or brown urine; plasma appears normal
ammonium sulfate precipitation method
historical method to differentiate hemoglobinuria from myoglobinuria
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
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
leukocyte esterase
normally few WBCs seen
greater than 20 u/L
a leukocyte indication of pathologic process (inflammation) from kidney (pyelonephritis) to urinary tract (urethritis)
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
lymphocytes
not detected in leukocyte esterase strip pad
10-25 WBCs/uL
amount detected in leukocyte esterase
nitrite
formed from nitrate reducing bacteria
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
glucosuria
presence of glucose in urine
glycosuria
presence of non-glucose sugars (fructose sucrose lactose) or combination in urine
glucose
not normally seen in normal urine
diabetes mellitus
most common disease that causes hyperglycemia and glucosuria
160-180 mg/dL
renal threshold for plasma glucose
galactose
most significant sugar other than glucose signifying inability to metabolize it into glucose (GALT seen in infants)
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
(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
ketones
breakdown products from large amounts of fatty acids
acetoacetate
principal form detected by reagent strip method
B-Hydroxybutyrate
not detected by strip tests
ketonuria
caused when blood ketone level exceeds 70 mg/dL; breath fruity; caused by starvation, bulimia, strenuous exercise, diabetes mellitus, or alcoholism
70 mg/dL
renal threshold for ketones
nitroprusside reaction
used to detect ketones; color change from beige to purple; positives always confirmed with Acetest
acetest
tablet test used to correctly identify ketones if truly present
bilirubin
seen in hepatic or post hepatic jaundice
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
ictotest
tablet test for confirmation of bilirubin in urine; detects even lower amounts than strip test; azo coupling of bilirubin with diazonium salt
urobilinogen
normally present in low amounts
Ehrlich's reaction
multistix
chemstrip
use azocoupling reaction specific for urobilinogen