A urine test will be one of the basic tests that is performed in a urine sample and would most probably be indicated in situations where a person complaints of burning sensation in the urine, difficulty in passing urine, discolored or foul smelling urine and in instances where systemic signs such as fever, nausea and vomiting indicate toward a possible urinary tract infection. Apart from these, it is a test that is performed routinely for many other investigative strategies.
There are many parameters shown in a urine test analysis and among them you might have noticed a parameter called nitrate or more specifically nitrite. Usually, the urine will contain a certain amount of nitrate but, in a normal urine sample, the nitrite will be indicated as ‘absent’ or ‘not present’. But, in certain instances, the nitrite can be indicated as being ‘present’ or “+”. In such instances, further evaluation has to be made as following reasons can give rise to such findings.
The commonest occurrence of positive nitrites in urine is in the presence of bacteria which is able to convert the non ionic nitrate into nitrite. Thus, the presence of nitrite is an indication to the presence of bacteria in the urine and therefore a urinary tract infection. The organisms can vary and would include certain species of E.coli , klebsiella, Proteus Sp., Pseudomonas…etc. It should be also noted that, the organisms which causes nitrate to become nitrite are almost exclusively of the gram negative variety.
Another reason for the presence of nitrite in urine is when there is a gross hematuria which will be obvious when the appearance of the urine becomes red or tea colored.
But, when interpreting these results, there are certain things that need to be remembered. One of these is the possibility of having ‘false positive results’ such as in the case of vaginal contamination of the urine sample and when the dipstick used to test for nitrites are exposed to air. In another instance, presence of phenazopyridine, which is a chemical used as an analgesic, can also give rise to a false positive result.
In other instances, ‘false negative results’ can appear in cases of higher urine levels of urobilinogen, specific gravity and in cases of bacteria which lacks the enzyme to reduce nitrates to nitrite. Another instance in which there might be a false negative result is when the patient is taking diets which lacks nitrates and in instances where the urine pH becomes less than 6.
In any instance, if nitrites are detected in the urine, further investigations should be carried out and its mere absence should not exclude any urinary infections.