This test is a rapid, indirect method for detecting bacteria in the urine. Significant UTI may be present in a patient who does not experience any symptoms. Common gram-negative organisms contain enzymes that reduce the nitrate in the urine to nitrite.

Healthcare providers frequently request the urine nitrite test to screen high-risk patients: pregnant women, school-age children (especially females), diabetic patients, elderly patients, and patients with a history of recurrent infections.

The majority of UTIs are believed to start in the bladder as a result of extreme contamination; if left untreated, they can progress to the kidneys. Pyelonephritis is a frequent complication of untreated cystitis and can lead to kidney damage. Detection of bacteria using the nitrite test and subsequent antibiotic therapy can prevent these serious complications. The nitrite test can also be used to evaluate the success of antibiotic therapy.

Negative for nitrites

1. Obtain a first morning specimen because urine that has been in the bladder for several hours is more likely to yield a positive nitrite test than a random urine sample that may have been in the bladder for only a short time. A clean-catch (midstream) urine specimen is needed to minimize bacterial contamination from adjacent anatomical areas.

2. Follow the exact testing procedure according to prescribed guidelines for reliable test results. Any shade of pink is positive for nitrite-producing bacteria.

3. Compare the reacted reagent area on the dipstick with a white background to aid in the detection of a faint pink hue that might otherwise be missed.

4. Perform a microscopic examination to verify results, if at all possible.

1. Under the light microscope, the presence of >20 bacteria per high-power field (hpf) may indicate a UTI. Untreated bacteriuria can lead to serious kidney disease.

2. The presence of a few bacteria suggests a UTI that cannot be confirmed or excluded until more definitive studies, such as culture and sensitivity tests, are performed. Again, this finding merits serious consideration for treatment.

3. A positive nitrite test is a reliable indicator of significant bacteriuria and is a cue for performing urine culture.

4. A negative result should not be interpreted as indicating absence of bacteriuria, for the following reasons:

   1. If an overnight urine sample is not used, there may not have been enough time for the nitrate to convert to nitrite in the bladder.

   2. Some UTIs are caused by organisms that do not convert nitrate to nitrite (e.g., staphylococci, streptococci).

   3. Sufficient dietary nitrate may not be present for the nitrate-to-nitrite reaction to occur.

Pretest Patient Care

1. Explain purpose of test, procedure for clean-catch (midstream) urine collection, and interfering factors.

2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. Azo dye metabolites and bilirubin can produce false-positive results.

2. Ascorbic acid can produce false-negative results.

3. False-positive results can be obtained if the urine sits too long at room temperature, allowing contaminant bacteria to multiply.

4. High SG will reduce the sensitivity.