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Test principle
Granulocyte esterases cleave a carboxylic acid indoxyl ester, the cleavage product reacts with a diazonium salt to form a violet dye.
Sensitivity
The practical sensitivity is around 10-20 leukocytes/µl.
Pathological: more than 20 leukocytes/µl
Specifity
Not only intact leukocytes are detected but lysed ones too, which are missed by the microscopic examination. Therefore, this excludes the sources of error of microscopic methods of investigation (counting
methods), which can occur in case of partial cytolysis of the leukocytes. pH fluctuations, nitrite, ascorbic acid, and ketone bodies do not have any influence. Urinary pathogenic bacteria and trichomonades do not react.
Sources of errors
  • Preservatives can generate false results (false-positive for formaldehyde).
  • False-negative results in urination with massive bacteriuria

  • Proteins (concentrations above 500 mg/dl) and glucose (over 2000 mg/dl) have a slightly inhibiting effect..

  • High doses of medicines such as cephalines, cephalothin, tetracycline and gentamicin can lead to weaker colour reactions.
  • Highly coloured urines (e.g. due to nitrofurantoin) can conceal the reaction colour with their own colour.
  • Avoid preserving the urine with hydrochloric acid, as a low pH value reduces the reaction of the esterases.
  • False-positive results can be caused by specimens which are contaminated by vaginal secretions.
Clinical significance
The detection of leukocytes in the urine (leukocyturia) is an important symptom of many inflammatory kidney and urinary tract diseases, in particular, it is the cardinal symptom for acute and chronic  pyelonephritis.
Leukocyturia occurs more frequently in women (30 to 40% positive) than in men.
Urine specimens of healthy people do not contain leukocytes.
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