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False-negative nitrite tests in urinary tract infections occur in cases with a low colony forming unit (CFU) count, or in recently voided or dilute urine. [4] In addition, a nitrite test does not detect organisms unable to reduce nitrate to nitrite, such as enterococci, staphylococci (Staphylococcus saprophyticus), Acinetobacter, or adenovirus. [4]
Nitrite-reducing bacteria need to remain in contact with nitrate for long enough to produce detectable amounts (first urine produced in the morning or at least with a urine retention of 4 hours). Large numbers of bacteria can react to reduce nitrite to nitrogen, which will give a false negative result.
A diet low in vegetables can lead to low nitrate levels in the urine, meaning that nitrites cannot be produced. [50] False positive results can occur in samples that are contaminated or stored improperly, allowing bacteria to multiply. [59]
Complementarily, the false negative rate (FNR) is the proportion of positives which yield negative test outcomes with the test, i.e., the conditional probability of a negative test result given that the condition being looked for is present. In statistical hypothesis testing, this fraction is given the letter β.
Reference ranges for urine tests are described below: Measurement Lower limit Upper limit ... Nitrite: n/a: 0 / negative [2] Leukocytes: n/a: 0 / negative [2] See also.
The nitrite test detects nitrate-reducing bacteria if growing in high numbers in urine. A negative dipstick test does not exclude bacteriuria, as not all bacteria which can colonise the urinary tract are nitrate-reducing. The leukocyte esterase test indirectly detects the presence of leukocytes (white blood cells) in urine which can be ...
Greenish urine can result from the consumption of asparagus or foods, [citation needed] beverages with green pigments, or from a urinary tract infection. [8] Blue urine can be caused by the ingestion of methylene blue (e.g., in medications) or foods or beverages with blue dyes. Blue urine stains can be caused by blue diaper syndrome.
A urine test is any medical test performed on a urine specimen. The analysis of urine is a valuable diagnostic tool because its composition reflects the functioning of many body systems, particularly the kidneys and urinary system , and specimens are easy to obtain. [ 1 ]