Limitations

• Limitations given for the reagents include specific substances and conditions that may affect the test results. 
• Because of specimen and reading variability, specimens with analyte concentrations that fall between nominal levels may give results at either level. Results will usually be within one level of the true concentration.
• As with all laboratory tests, definitive diagnostic or therapeutic decisions should not be based on any single results or method.
• Color Interferences: Substances that cause abnormal urine color may affect the readability of reagent areas on urinalysis reagent strips.  These substances include visible levels of blood or bilirubin, drugs containing dyes (for example, Pyridium, Azo Gantrisin, Azo Gantanol), nitrofurantoin (Macrodantin, Furadantin), and riboflavin.
• Protein: 
  • False positive results may be obtained with highly buffered or alkaline urine, or in the presence of quinidine, chlorhexidine, chloroquine, or Lodine (etodolac).
  • The presence of hemoglobin (≥ 5 mg/dL) may cause elevated results.
  • False negative results may occur if curcuma is present.
• Blood: 
  • Captopril (Capoten) and other compounds containing sulfhydryl groups may reduce the sensitivity. 
  • Certain oxidizing contaminants, such as hypochlorite, may produce false positive results. 
  • Microbial peroxidase associated with urinary tract infection may cause a false positive reaction.
  • False negative results may occur in the presence of acetylcysteine, ascorbic acid, formalin, quinidine, cefoxitin, levodopa, mesna, Keflin, curcuma, Lodine, hydrochlorothiazide, metformin, chlorhexidine, or chloroquine.
• Leukocytes: 
  • Elevated glucose concentrations (≥3 g/dL) may cause decreased test results. 
  • False negative results may occur in the presence of quinidine, boric acid, Tagamet, glycine, chloroquine, sulfamethoxazole, chlorhexidine, nitrofurantoin, Lodine, hypochlorite,glyburide, or calcium chloride.
  • The presence of cephalexin (Keflex), cephalothin (Keflin), or high concentrations of oxalic acid may also cause decreased test results.Tetracycline may cause decreased reactivity, and high levels of the drug may cause a false negative reaction.
  • Positive results may occasionally be due to contamination of the specimen by vaginal discharge or the presence of formalin or curcuma.
  • High specific gravity may cause falsely low leukocyte results.
• Nitrite: 
  • A negative result does not rule out significant bacteriuria. 
  • False negative results may occur with shortened bladder incubation of the urine, absence of dietary nitrate, or the presence of nonreductive pathological microbes, ascorbic acid, Lodine, formalin, chlorhexidine, or oxalic acid. 
  • The presence of color precipitates may cause a false positive result.
• Glucose: 
  • Urine samples with a pH of 9.0 and greater will cause falsely elevated glucose results.
  • False positive results may occur in the presence of hypochlorite, ascorbic acid, captopril, mesna, or curcuma.
  • Ketone bodies reduce the sensitivity of the test. Moderately high ketone levels may cause false negatives for specimens containing small amounts of glucose.
• Ketone: 
  • False trace results may occur with highly pigmented urine specimens or those containing large amounts of levodopa metabolites. 
  • Compounds that contain sulfhydryl groups, such as mesna (2-mercaptoethane sulfonic acid) and captopril, as well as acetylcysteine, curcuma, formalin, imipenem, or hydrochlorothiazide may cause false positive results or an atypical color reaction.
  • False negative results may occur in the presence of boric acid, formalin, hypochlorite, meropenem, or Lodine.
• pH: 
  • Bacterial growth by certain organisms in a specimen may cause a marked alkaline shift (pH > 8.0), usually because of urea conversion to ammonia.
• Bilirubin: 
  • Indican (indoxyl sulfate) can produce a yellow-orange to red color response that may interfere with the interpretation of a negative or positive reading. 
  • Metabolites of etodolac (Lodine) may cause false positive or atypical results.  Atypical colors may indicate the presence of bile pigment abnormalities and the urine specimen should be tested further.
  • The presence of p-aminosalicylic acid, may give a false positive result.
  • A false negative may occur in the presence of acetylcysteine, ascorbic acid, boric acid, hypochlorite, captopril, mesna, nitrite, curcuma, citric acid, chlorhexidine, or oxalic acid.
  • Atypical colors may indicate that bile pigments are present in the urine specimen and may be masking the bilirubin reaction.
• Urobilinogen: 
  • The reagent area may react with interfering substances known to react with Ehrlick’s reagent, such as ρ-aminosalicylic acid and fulfonamides. 
  • False negative results may be obtained if formalin, acetylcysteine, captropril, hypochlorite, mesna, Tagamet, curcuma, Lodine, sulfamethoxazole,chlorhexidine, glucose, hydrochlorothiazide, lactose, meropenem, or nitrofurantoin is present. 
  • The test is not a reliable method for the detection of porphobilinogen.
• Specific Gravity: Measurement of specific gravity by refractometry may be influenced by high levels of urinary glucose and protein which can cause underestimation of the actual specific gravity.