Specific Sources of Error with Reagent Strip
Testing
Urinalysis and Body
Fluids Review 494
INCREASED OR FALSE POSITIVE DECREASED OR FALSE NEGATIVE
pH
Protein
Glucose
Ketones
Blood
Bilirubin
Urobilinogen
Nitrite
Acid runover from protein square.
Proteins other than albumin.
Unpreserved specimen, ↑ascorbic acid, ↑SG, ↓temp.
Improper storage. Acetone is volatile. Bacteria break down
acetoacetic acid.
↑ascorbic acid, ↑nitrite, ↑SG (crenated RBCs), unmixed
specimen.
Exposure to light, ↑ascorbic acid, ↑nitrite.
Improperly preserved specimen (oxidation to urobilin),
formalin.
Non-nitrate-reducing bacteria, inadequate time in bladder,
reduction of nitrites to N2, ↓dietary nitrate, antibiotics,
↑ascorbic acid, ↑SG.
Improperly preserved specimen
Highly buffered alkaline urine, prolonged
dipping, contaminated container, ↑SG
Contamination with peroxide or bleach
Red pigments, dyes, some meds
Menstruation, oxidizing agents, bacterial
peroxidase
Highly pigmented urine
Highly pigmented urine
Highly pigmented urine, improperly
preserved specimen (contaminating
bacteria produce nitrites)
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