Nitrite in urine may arise in vivo and is found in normal urine in low concentration. Patients receiving medications such as nitroglycerine, isosorbide dinitrate, nitroprusside, and ranitidine may have increased nitrite levels in their blood. However, concentrations of nitrite were below 36 |g/mL in specimens cultured positive for microorganisms, and nitrite concentrations were below 6 |g/mL in patients receiving medications that are metabolized to nitrite. On the other hand, nitrite concentrations were 1910-12,200 |g/mL in urine specimens adulterated with nitrite (23). The authors analyzed nitrite concentrations in urine utilizing a Lachat QuickChem® AT automated continuous-flow analyzer (Lachat Instruments) using a protocol approved by the US Environmental Protection Agency.
Whizzies is another urine adulterant that contains potassium nitrite. The presence of nitrite in urine can be detected by a simple spot test using a standard solution of 2% potassium permanganate in distilled water and 2 N hydrochloric acid solution (22). If nitrite is present in the urine sample, the pink permanganate solution turned colorless with effervescence immediately after addition of hydrochloric acid. This is because of reduction of heptavalent manganese ion of potassium permanganate by nitrite. The presence of very high glucose (>1000 mg/dL) and ketone bodies in urine may cause false positives. However, this may take approx 2-3 min for the solution to turn colorless, whereas if nitrite is present, the solution turns colorless immediately. The potassium iodide spot test, which is effective to detect the presence of chromate in urine, can also be used for detection of nitrite (22). After addition of a few drops of 2 N hydrochloric acid, immediate release of iodine from the colorless potassium iodide solution is observed. As described earlier, shaking of this solution with n-butanol results in the transfer of iodine into the organic phase. If no nitrite is present, the potassium iodide solution remains colorless. No interference from high glucose or ketone bodies is observed if present in the urine.
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