The usefulness of rapid screening tests in discriminating normal and infected urine specimens under Sri Lankan conditions

Abstract

INTRODUCTION: Tropical climate and improper specimen collection can lead to contamination of urine by the commensal flora and their rapid multiplication prior to the culture. In Sri Lanka, some laboratories use the centrifuged urine for estimating pus cell counts whilst others use the un-centrifuged urine. OBJECTIVE: To assess the usefulness of rapid and simple screening tests for UTI currently available in Sri Lanka STUDY DESIGN: A prospective study over a three months period. SETTINGS: Urine specimens referred to University laboratory from wards of the Teaching Hospital, Ragama. METHODS: Midstream urine specimens from 100 patients presenting with a history of UTI, collected prior to antibiotic therapy were examined within one hour of collection for the determination of urine pus cell and organism counts, nitrate reduction (NR) and leukocyte esterase (LE) activity and the significant bacteriuria. Organism and pus cell counts of un-centrifuged and centrifuged urine using a Neubauer haemocytometer and per high power field (PHF) were examined by microscopy. RESULTS: 28 out of 100 patients enrolled in the study, had significant bacteriuria (>105 colony forming units (CFU) /ml) whilst 17/100 had 'may be significant1 (104'105 CFU/ml) and 55/100 had <104 CFU/ml bacteriuria. The sensitivity and specificity of using the pus cell count /ml of un-centrifuged urine using a Neubauer haemocytometer, compared to the culture positive samples was 71.42%(20/28) and 89.09% (49/55) respectively, at the cut off point of 10s pus cells/ml. The sensitivity and specificity of pus cell count /HPF in un-centrifuged urine was 14.3% (4/28) and 96.4% (53/55) respectively whilst the counts /HPF in centrifuged urine was 57% (16/28) and 91% ( 50/55) respectively. The sensitivity and specificity of the presence of both NR and LE activity in relation to culture was 82.1% and 27.3 % respectively. CONCLUSIONS: The pus cell count/ml of un-centrifuged urine is a better indicator of UTI at the cut off point of 105 pus cells/ml compared to the count per HPF or urine NR and LE activity. Pus cell counts/HPF or organism counts in both un-centrifuged and centrifuged urine were found to have a lower co-relation with the culture positive samples. However, amongst the screening tests assessed, the pus cell count/ml of un-centrifuged urine is superior in terms of sensitivity, specificity and the reliability.