Page 38 - Clinical Biochemistry 08PB804

Figure 7: RBCs in the urine

6- Nitrite
• Nitrite indicates urinary tract infection (i.e. E. coli pseudomonas,….. etc).
• Bacteriuria caused by some Gram negative bacteria which produce the nitrate reductase
enzyme that convert nitrate (derived from the diet) to nitrite.
• Staphylococcus is an exception.
• False positive: contaminated sample.
• False negative: antibiotic therapy.
7- Protein in Urine < 150 mg/24 hrs
• Dipstick screening for protein is done on whole urine, but Semi-quantitative tests for urine
protein should be performed on the supernatant of centrifuged urine (as cells suspended in
urine can produce false high protein levels).
• More than 150 mg/day is defined as proteinuria. Proteinuria > 3.5 gm/24 hours is severe
and known as nephrotic syndrome.
• Bromphenol blue (an indicator dye) in Dipsticks is most sensitive to albumin but not to
globulins.
• Urinary dipstick becomes positive when the protein values exceed 300-500 mg/day.
8. Leukocyte esterase
• Leukocyte esterase, is released when WBCs undergo lysis.
• Pyuria (presence of Pus or > 6 WBCs) can be detected.
• A positive leukocyte esterase test result indicates pyuria.
III- Microscopic Exam