Urinalysis Dipstick Flashcards
chemical reaction of pH reagent strip
methyl red + (H+) → bromothymol blue - (H+)
(red-orange → yellow) (green → blue)
chemical reaction of protein reagent strip
indicator (yellow) + protein —(pH 3.0)→ protein + (H+) OR indicator - (H+)
(blue-green)
chemical reaction of glucose reagent strip
- glucose + O2 —(glucose oxidase)→ gluconic acid + H2O2
- H2O2 + chromogen —(peroxidase)→ oxidized colored chromogen + H2O
chemical reaction of ketone reagent strip
acetoacetate + acetone + sodium nitroprusside + glycine —(alkaline)→ purple color
chemical reaction of blood reagent strip
H2O2 + chromogen —(hemoglobin peroxidase)→ oxidized chromogen + H2O
chemical reaction of bilirubin reagent strip
bilirubin glucuronide + diazonium salt —(acid)→ azo dye
chemical reaction of urobilinogen reagent strip
urobilinogen (Ehrlich’s reactive substances) + p-dimethylaminobenzaldehyde (Ehrlich’s reagent) —(acid)→ red color
chemical reaction of nitrite reagent strip
Greiss reaction:
- aromatic amine in reagent strip reacts with nitrite, producing diazonium salt
- diazonium salt (arsinilic acid) reacts with sulfanilic acid and acetic acid to produce a pink azo dye
chemical reaction of leukocyte esterase (LE) reagent strip
indoxylcabonic acid ester —(leukocyte esterase)→ indoxyl + acid indoxyl + diazonium salt —(acid)→ purple azo dye
chemical reaction of specific gravity (SG) reagent strip
- based on pKa (dissociation constant) of polyelectrolyte in alkaline medium
- poly electrolyte ionizes, releasing H+ in relation to concentration of urine
- higher concentration = more H+ released
- bromothymol blue measures pH change
pH reaction interferences
none
protein reaction interferences
- FP (4)
- FN (1)
FP:
- highly buffered alkaline urine (overrides acid buffer system)
- highly pigmented urine
- high SG
- quaternary ammonium compounds, detergents, antiseptics, chlorhexidine
FN:
- dilute speciment
glucose reaction interferences
- FP (3)
- FN (6)
FP:
- oxidizing cleaning agents
- peroxide
- hypoclorite (bleach)
FN or decreased sensitivity:
- cold specimens (slows down reaction)
- increased SG
- alkaline pH
- increased ketones
- high dose of ascorbic acid (mega-dose of vitamin C)
- testing old samples (bacteria eats glucose)
ketones reaction interferences (2)
- FP (1)
- FN (1)
- levodopa in large dosages
- medications containing sulfhydryl groups (produces atypical color reactions)
FP:
- improperly timed readings
FN:
- improperly preserved specimens (breakdown of acetoacetic acid)
blood reaction interferences
- FP (3)
- FN (4)
FP:
- menstrual contamination
- strong oxidizing agents (bleach)
- bacterial peroxidases
FN:
- ascorbic acid
- high SG/crenated cells
- high concentrations of nitrite
- unmixed specimens
bilirubin reaction interferences
- FP (3)
- FN (3)
FP:
- urine pigments
- pyridium (phenazopyridine) → UTI drug
- drugs lodine (NSAID) → arthritis
FN:
- old specimens (bilirubin oxidizes to biliverdin)
- large amounts of ascorbic acid
- nitrite + diazonium salt = blockage of bilirubin reaction
urobilinogen reaction interferences
- FP (2)
- FN (5)
FP:
- p-aminosalicylic acid
- sulfonamides
FN:
- broad spectrum antibiotics
- urine nitrites and formalin preservatives
- improper storage of specimen
- loss of intestinal bacteria (conjugated bilirubin would not convert to urobilinogen)
- biliary obstruction (ex. kidney stone)
nitrite reaction interferences
- FP (3)
- FN (6)
FP:
- old specimen
- highly pigmented urine
- pink edge/spotting on reagent strip is considered negative
FN:
- nonreductase-containg bacteria (bacteria that doesn’t convert nitrates to nitrites)
- insufficient contact time between bacteria and nitrate
- large quantities of bacteria converting nitrite to nitrogen
- high SG
- high concentrations of ascorbic acid and urobilinogen
- lack of nitrates
leukocyte esterase reaction interferences
- FP (1)
- FN (3)
FP:
- strong oxidizing agents
FN:
- high concentrations of protein or glucose
- crenation from high SG
- inaccurate timing
SG reaction interferences
- decreased readings → pH 6.5 or higher
interferes with indicator
pH clinical sig.
when increase of pH occurs:
- after meals
- vegetable heavy diet
when decrease of pH occurs:
- during sleep
- protein heavy diet
- some foods produce acid, decreasing pH
- metabolic disorders (ex. diabetes mellitus; patients produce keto-acids)
leukocyte esterase clinical sig.
presence of WBCs in urine suggests infection and inflammation
nitrite clinical sig.
presence of bacteria that reduce nitrates to nitrites; commonly seen in UTIs
protein clinical sig.
may indicate kidney disease, hypertension, or diabetes
