Nitrites Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Nitrites and links to relevant pages within the course.
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| Match the following reagent strip tests to the disease or disorder that would most likely cause a positive test result. | View Page |
| False Negative Results False negative bilirubin dipstick results are often due to testing a specimen that is not fresh. Bilirubin breaks down when exposed to light. Indoxyl sulfate (Indican) can produce a yellow orange-to-red color response which may interfere with the interpretation of a positive or negative reaction. Positive nitrites due to a urinary tract infection may also cause a false negative result. | View Page |
| Which of the following may cause a false positive bilirubin result on a urine reagent strip? | View Page |
| Which of the following may cause false negative bilirubin results on a urine reagent strip? (Choose ALL of the correct answers) | View Page |
| False Negative Results False negative results may occur with some methods when the concentration of ascorbic acid is greater than 5 mg/dL. The sensitivity of the blood portion of the test strip is decreased in specimens with a high specific gravity and increased protein. High levels of nitrites may delay the reaction, causing a false negative to be reported. If the pH of a urine sample is below 5, hemolysis of red cells as part of the test reaction is inhibited which results in a false negative reaction. An improperly mixed specimen may test negative if the red blood cells are in the sediment. | View Page |
| Nitrite Test The nitrites portion of the reagent strip provides a rapid screening test for the presence of gram-negative bacteria that are often responsible for urinary tract infections. Although urine cultures are still needed to confirm the diagnosis and monitor any urinary tract or kidney infection, the need for a culture may not be obvious because in some cases of early bladder infection, the symptoms may be vague or the patient may be asymptomatic. Diagnosis and treatment of cystitis (bladder infection) is important because if left untreated it may result in kidney damage, impairment of renal function, hypertension and/or septicemia. | View Page |
| Bladder Infections Bladder infections are usually caused by gram-negative bacteria. These bacteria reduce nitrates derived from food to nitrites when urine remains in the bladder three to four hours, sufficient time for this reaction to occur. Nitrite is not present in urine under normal circumstances. When present, nitrites react with p-arsanilic acid to produce a diazonium compound. The diazonium compound in turn couples with 3-hydroxy-1,2,3,4 tetrahydrobenzo-(h)-quinolin to produce a pink color. A first morning, clean, voided midstream specimen is optimal for detecting nitrites in urine. | View Page |
| Test Sensitivity This test is sensitive to 0.06-0.1 mg/dL nitrite ion in urines with a low specific gravity and ascorbic acid concentrations of less than 25 mg/dL. Pink spots or pink edges should not be interpreted as a positive result because some medications can color urine red or turn red in an acid environment. Any degree of uniform pink color should be considered positive, suggesting the presence of 105 organisms/mL. Detection of low levels of nitrite ion may be enhanced by comparing the activated test strip to a white background. It is important to note that color development is NOT proportional to the number of bacteria present. The test is specific for nitrites and does not react with any other substances normally present in urine. Negative results do not necessarily rule out a urinary tract infection because yeasts or gram-positive bacteria unable to reduce nitrites may be the causative agent. | View Page |
| False Positive Results A false positive nitrite test result may occur when a urine specimen has remained at room temperature for an extended period of time, allowing bacterial contaminants to multiply and produce measurable levels of nitrites. Interference from some medications that cause the urine to become red or orange may lead to an incorrect reading of positive for nitrite. | View Page |
| Nitrates in urine are reduce to nitrites by: | View Page |
| Which of the following substances cause a false-positive reaction on the urobilinogen portion of the test strip? (Choose ALL of the correct answers) | View Page |
| False-negative results on reagent strips for leukocytes may occur when the specimen contains: (Choose ALL of the correct answers) | View Page |
| S. milleri Biochemicals The combination of decarboxylation of arginine (red color in the 2nd tube from left compared to the yellow color of the control to its left), the hydrolysis of esculin (black pigment in the esculin agar tube) and the reduction of nitrates to nitrites (red color in last tube on the right) are biochemical characteristics confirmatory for S. milleri (anginosus). | View Page |
| Eikenella biochemicals Although not performed that often, the following tests are useful in separating E. corrodens from other closely related members of the HACEK group:KIA showing an alk/alk reaction;
Glucose fermentation (-);
Reduction of nitrates to nitrites (+);
Production of indole (-);
Ornithine decarboxylase (+)
The positive nitrate reduction reaction eliminates Cardiobacterium hominis, Kingella kingae and other Kingella species.The positive ornithine decarboxylase reaction eliminates Kingella denitrificans (which also denitrifies nitrate to nitrogen gas, a reaction negative for E. corrodens).Eikenella corrodens is asaccharolytic, whereas most other closely related species produce acid from one or more carbohydrates. | View Page |