Reference Values

Glucose:  negative

Blood:  negative

Bilirubin:  negative
Ketones:  negative
Protein:  negative
Urobilinogen:  0.2-1.0 EU/dL

Nitrate:  negative
Leukocyte esterase:  negative

WBC:  0-5/hpf
RBC:  0-2/hpf
Crystals:  any identified

Critical values (automatic call-back):  cystine, leucine, or tyrosine, glucose or ketone positive on a newborn

Interfering Substances:

Color:  Drugs containing azo dyes (eg, pyridium, azo gantrisin, azo gantanol) nitrofurantoin (macrodantin, furadantin) and riboflavin, may affect the readability of reagent areas on urinalysis reagent strips. The color development on the pad may be masked, or a color reaction may be produced on the pad that could be interpreted visually and/or instrumentally as a false-positive result.

Glucose:  Ascorbic acid concentrations of ≥50 mg/dL may cause a false-negative result for a specimen containing small amounts of glucose (75-125 mg/dL). Ketone bodies reduce the sensitivity of the test:  moderately-high ketone levels (40 mg/dL) may cause a false-negative result for a specimen containing small amounts of glucose (75-125 mg/dL) but the combination of such ketone levels and low glucose levels is metabolically improbable in screening. The reactivity of the glucose test decreases as the specific gravity of the urine increases.

Bilirubin:  Indican can produce a yellow-orange to red color response that may interfere with the interpretation of a negative or positive bilirubin reading. Metabolites of iodine may cause false-positive or atypical results:  ascorbic acid concentrations of ≥25 mg/dL may cause a false-negative result.

Ketone:  False-positive results (less than a trace) may occur with highly pigmented urine specimens or those containing large amounts of levodopa metabolites. Compounds such as mesna that contains sulfhydryl groups may cause false-positive results or an atypical color reaction.

Specific gravity:  The chemical nature of the AMES specific gravity test may cause slightly different results from those obtained with other specific gravity methods when elevated amounts of certain urine constituents are present. Highly buffered alkaline urines may cause low readings relative to other methods. Elevated specific gravity readings may be obtained in the presence of moderate quantities (100-175 mg/dL) of protein.

Blood:  Elevated specific gravity may reduce the reactivity of the blood contaminants, such as hypochlorite, may produce false-positive results. Microbial peroxidase associated with urinary tract infection may cause a false-positive reaction. Levels of ascorbic acid normally found in the urine do not interfere with this test.

Protein:  False-positive results may be obtained with highly buffered or alkaline urines. Contamination of the urine specimen with quaternary ammonium compounds (from some antiseptics and detergents) or with skin cleansers containing chlorhexidine may also produce false-positive results.

Urobilinogen:  Atypical color reactions may be obtained in the presence of high concentrations of p-aminosalicylic acid. False-negative results may be obtained if formalin is present. Strip reactivity increases with temperature. The test is not a reliable method for the detection of porphobilinogen. The absence of urobilinogen cannot be determined with this test.
Nitrates:  A negative result does not in and of  itself prove that there is no significant bacteriuria. Negative results may occur when urinary tract infections are caused by organisms that do not contain reductase to convert nitrate to nitrite; when urine has not been retained in the bladder long enough (≥4 hours) for reduction of nitrate to nitrite to occur, or when dietary nitrate is absent, even if organisms containing reductase are present and bladder incubation is ample. Sensitivity of the nitrate test is reduced for urines with high specific gravity. Ascorbic acid concentrations of ≥25 mg/dL may cause false-negative results with specimens containing small amounts of nitrite ion (≤0.06 mg/dL).

Leukocytes:  Elevated glucose concentration (≤3 g/dL) or high specific gravity may cause decreased test results. The presence of cephalexin, cephalothin, or high concentrations of oxalic acid may also cause decreased test results. Tetracycline may decrease reactivity, and high levels of this drug may cause a false-negative reaction.