March 16, 2011 by dailybolusoflr
Urine nitrite on dipstick evaluation is used to detect bacteria and is used by clinicians to diagnose UTI in patients.
Nitrites normally are not found in urine but can be found when bacteria are present that reduce urinary nitrates to nitrites.
· Many gram-negative and some gram-positive organisms are capable of this
· A positive urine nitrite on dipstick indicates that these organisms are present in significant numbers to cause infection (typically > 10,000 per cc)
Urine nitrite is specific but not highly sensitive for UTI (specificity 92-100%, sensitivity 19-48%)
· A positive result is suspicious for the presence of bacteria
· A negative result does not rule out UTI
False Positive Test
· Urine that has remained at room temperature for an extended period of time with multiplication of bacteria to levels that produce a detectable urine nitrite.
· Uncapped vial
o when the reagent strips are exposed to air the number of strips giving a false positive increases…. By the end of a week of exposure, one-third of the nitrite tests gave false-positive readings. At the end of a second week, nearly three-quarters gave false-positive readings, for a specificity of only 28%.
Simerville JA, Maxted WC, Pahira JJ. Urinalysis: a comprehensive review. Am Fam Physician2005;71(6):1153-62.
Gallagher EJ, Schwartz E, Weinstein RS. Performance characteristics of urine dipsticks stored in open containers. Am J Emerg Med1990;8(2):121-3.
Linda Regan, MD FACEP
Program Director, Emergency Medicine Residency
Johns Hopkins Medical Institutions