Nitrites in Urine


Introduction

A urine test is a screening or diagnostic tool that may be requested by a physician to analyze the composition and compounds found in the urine. When certain substances, such as nitrites, are present in an individual’s urine, it is an indication that there is an underlying pathological condition [1, 2, 3].

What is Nitrites in Urine?

The presence of nitrites in the urine, also called as nitrituria, is a good indication that the individual has a urinary tract infection (UTI). Nitrites is formed when gram-negative bacteria metabolizes the commonly occurring urinary nitrates.

The precursor nitrates is obtain from eating vegetables such as lettuce, celery, spinach and red beetroot. Gram-negative bacteria such as E.coli, Pseudomonas Sp., Klebsiella and Proteus Sp., are able to convert the nitrate to nitrates. It is important to note that not all pathogens are able to produce the compound that is being tested. The nitrite test is a good indicator but a negative nitrite test does not necessarily mean that the person does not have UTI. He may be infected with a pathogen that is not able to convert urinary nitrates [2, 3, 4].

Nitrite Urinary Test

In testing for nitrite in the urine, using the first urine of the day is desired. It must have been incubating inside the bladder for at least 4 hours. A special kit that contains sterile cup and wipes is used to collect the sample. Maintaining the sterility of the sample is crucial as it will be able to provide the most accurate result [5, 6].

The clean catch techniques is done to avoid contamination of the urine sample. Hands must be washed prior to obtaining the sample. Females should clean their vulva and perianal area using the wipes that have been provided. Wiping should be done from front to back. For males, there will be a need to retract the foreskin if he is uncircumcised.


The penis should be wiped from the tip to the base twice. Urinate a small amount into the toilet and then consciously hold the urine. Hold the container in front of the urethra to obtain the sample. Care must be observed to prevent any skin from touching the container. After filling half of the container, place it in a stable surface while you finish urinating [5, 6].

Label the sample properly and submit it to the physician right away. The urine must be tested within an hour of the collection of the urine because an old sample may give an accurate result. The sample should be refrigerated if it will be more than 30 minutes before the sample can be submitted. The medical professional will either do a chemical analysis or a dipstick test on the sample urine to identify the presence of nitrite in the urine. Figure 1 illustrates a color block change in a urinary nitrite dipstick test [5, 6].


Nitrites in Urine DipStick Test Positive


Figure 1- Nitrite Dipstick Test

Clinical Significance of Nitrites in Urine

An individual who have been positive for a nitrite test is usually suffering from a UTI. When a patient who is experiencing symptoms such as painful urination and fever consults a physician, a urinary nitrite test may be requested to confirm the diagnosis.

A urine culture and susceptibility test may be ordered afterwards to identify the pathogen and the most appropriate antibiotic agent to resolve the infection. It is advised for the patient to finish the entire course of the treatment to prevent the reoccurrence. It is able advisable for the patient to increase the amount of fluid intake to help flush the bacteria out of the system [3, 4].

Negative

A person who presents with symptoms but has a negative nitrite test does not mean that he has no UTI. Only gram negative bacteria are able to convert the nitrate into nitrite. He may have been infected with a pathogen that are unable to produce nitrite. The pathogen will be identified through a urinary culture and will be given an appropriate course of antibiotic treatment [2, 3, 4].

False Positive

It is also possible to have a false positive reading if the urine is not yet tested right away. If the urine sample is maintained at room temperature, it will be contaminated by bacteria and this will give a false positive nitrite reading. It is essential to follow the instructions of the clean-and-catch kit and submit the sample right away to avoid getting a false result [2, 3, 4].


References

  1. Labtests Online. (2015). Retrieved from Labtests Online: https://labtestsonline.org/understanding/analytes/urinalysis/ui-exams/start/1#nitrite
  2. (2014, September 9). Urine Test. Retrieved from WebMD: http://www.webmd.com/a-to-z-guides/urine-test
  3. (2015, October 21). Nitrates or Nitrites in Urine. Retrieved from Minimedia: http://minimemedia.com/nitrates-in-urine/
  4. (2015). Urinary Nitrites and Leukocyte Esterase. Retrieved from RNceus: http://www.rnceus.com/ua/uanile.html
  5. Kirkwood, J. (2016, January 5). Clean Catch Urine Sample and Culture. Retrieved from Healthline: http://www.healthline.com/health/urine-culture-clean-catch#Overview1
  6. Vorvick, L. (2016, March 2). Clean catch urine sample. Retrieved from Medline Plus: https://www.nlm.nih.gov/medlineplus/ency/article/007487.htm

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