From the Guidelines
A nitrite positive urine test is primarily caused by the presence of certain bacteria in the urinary tract, specifically those that can convert nitrates to nitrites, such as gram-negative organisms like Escherichia coli, Klebsiella, Proteus, Enterobacter, and Citrobacter species, as supported by the most recent evidence 1. The most common bacteria responsible for this conversion possess an enzyme called nitrate reductase that facilitates this conversion. When these bacteria infect the urinary tract, they metabolize nitrates (which are normally present in urine from dietary sources) into nitrites, resulting in a positive nitrite test on urinalysis. This finding is highly suggestive of a urinary tract infection (UTI), particularly when accompanied by other symptoms like dysuria, frequency, urgency, or cloudy urine. Some key points to consider include:
- Not all UTIs will produce a positive nitrite test, as some pathogens like Enterococcus, Staphylococcus, and Pseudomonas do not convert nitrates to nitrites 1.
- For the test to be positive, urine needs to remain in the bladder for at least 4 hours to allow sufficient time for the bacterial conversion process 1.
- False negatives can occur with frequent urination, low dietary nitrate intake, or infections with non-nitrate-reducing organisms 1.
- The presence of either nitrite or leukocyte esterase has a sensitivity of 88% and a false positive rate of 7% for urinary tract infection, and if both tests are positive, the specificity is 96% 1.
- Escherichia coli is the most common organism causing UTIs, accounting for approximately 75% of cases, with other infections caused by Enterococcus faecalis, Proteus mirabilis, Klebsiella, or Staphylococcus saprophyticus 1.
- Urinalysis, including assessment of white and red blood cells and nitrite, is recommended for routine diagnosis of UTIs, and a urine culture and antimicrobial susceptibility testing should be performed in all cases of pyelonephritis 1.
From the Research
Causes of Nitrite Positive Urine Test
- A nitrite positive urine test is often an indication of a urinary tract infection (UTI) caused by certain bacteria, such as Escherichia coli, that are capable of reducing nitrate to nitrite 2, 3, 4.
- The presence of nitrite in urine is highly specific for UTI, but the test may not be highly sensitive, meaning that a negative result does not necessarily rule out an infection 4, 5.
- Factors that can affect the accuracy of the nitrite test include the type of bacteria causing the infection, the concentration of nitrate in the urine, and the presence of substances that can interfere with the test, such as ascorbic acid 5.
- Other causes of a nitrite positive urine test may include:
- Bacterial infections other than UTI, such as those caused by Enterobacterales species 5.
- Contamination of the urine sample with bacteria from the skin or other sources.
- Certain medical conditions, such as kidney disease or diabetes, that can affect the concentration of nitrate in the urine.
- It's worth noting that a nitrite positive urine test should be interpreted in the context of the patient's symptoms and medical history, and should be confirmed with a urine culture if possible 2, 6.
Bacteria that can Cause Nitrite Positive Urine Test
- Escherichia coli (E. coli) is the most common cause of UTI and is often associated with a nitrite positive urine test 2, 3, 4.
- Other bacteria that can cause a nitrite positive urine test include:
Limitations of the Nitrite Test
- The nitrite test is not highly sensitive, meaning that a negative result does not necessarily rule out an infection 4, 5.
- The test can be affected by factors such as the type of bacteria causing the infection, the concentration of nitrate in the urine, and the presence of substances that can interfere with the test 5.
- The test should be interpreted in the context of the patient's symptoms and medical history, and should be confirmed with a urine culture if possible 2, 6.