Nitrate Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Nitrate and links to relevant pages within the course.
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| A patient suspected of a urinary tract infection has a negative nitrite test, but bacteria is present upon microscopic examination. What may have caused a false-negative result? (Choose ALL of the correct answers) | View Page |
| Procedure Caution Although the procedure is simple to perform, accurate results depend on careful adherence to manufacturer’s directions and adequate quality control. Normal and abnormal controls should be tested whenever a new lot of strips is opened, and at the frequency defined by the laboratory's procedure. If quality control results do not correspond to the published control values, the problem must be resolved before patient samples are tested. High levels of ascorbic acid (Vitamin C) in the urine may inhibit some reagent strip reactions, such as glucose, blood, bilirubin, nitrate and leukocyte esterase. The urine dipstick's package insert will provide information about potential interfering substances, including ascorbic acid. Intensely colored urine may make it difficult to correctly interpret color reactions on the dipstick. The affected tests should not be reported from the dipstick. It would be necessary to use an alternative method of testing if available. | View Page |
| False Negative Results False negative results may occur in urine specimens that did not remain in the bladder a sufficient length of time for the bacteria to reduce a measurable quantity of nitrate to nitrite. Other reasons for false negative results include high specific gravity, ascorbic acid levels above 25mg/dL or low pH (<6). Less frequently, the cause may be due to a lack of sufficient nitrate in the diet (green vegetables) or further reduction of nitrite to nitrogen when large numbers of bacteria are present. In patients receiving antibiotics, the metabolism of the bacteria may be inhibited which would also produce a false negative reaction. | View Page |
| Different species of Neisseria can be differentiated from each other by: | View Page |
| Which of the following is not true about members of the Enterobacteriaceae: | 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 |