Nitrates are ions that are in the green
vegetables that we consume in our diets. Nitrates are converted to nitrites
when there is a bacterial infection in the urinary tract. If a patient is
suffering from a urinary tract infection that is caused by gram-positive
bacteria the nitrite dip-strip test may come out as negative. This false
negative is seen because certain gram-positive bacteria may not produce enzymes
needed to convert nitrate to nitrite. False
results may also be seen if the urine sample contains a high concentration of
most common way to detect nitrites in urine is by using a dip-strip test. The
reagent strip is founded on the Griess test and involves a diazo reaction.
Nitrite reacts with an aromatic amine (such as p-arasnilic or sulfanilic acid)
in an acid medium to create a diazonium salt. This salt will then react with
another aromatic ring to produce an azo dye. The azo dye will produce a pink or
red color on the strip, and this color is what signifies a positive result for
nitrite in the urine.
Chromatography can also be used to determine
nitrite levels in urine. Ion chromatography, gas chromatography, and high-performance
liquid chromatography are all examples of chromatography that could be used in
nitrite tests include electron paramagnetic resonance, spectrophotometry,
infrared spectrophotometry, fluorescence probe, chemiluminescence and capillary
electrophoresis. These tests are not cost-effective and take a long time to
complete and therefore, are rarely used.
conclusion, the negative nitrite results for this patient, whom is suffering
from an Escherichia coli infection was
due to the fact the patient was also suffering from frequent urination. Frequent urination causes the urine sample collected
to not be retained in the bladder long enough for the Escherichia coli to release enzymes to convert nitrate into
nitrite. To get an accurate urinalysis, the urine sample must be retained in
the bladder for at least four hours, which ensures that bacteria in the urine
had enough time to release reducing enzymes to convert nitrate into a
detectable amount of nitrite.