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The volume of urine
collected affected the test performances of the ligase chain
reaction and the transcription mediated amplification assays for
detection of C. trachomatis.
Volume effect on sensitivity of
nucleic acid amplification tests for detection of Chlamydia trachomatis
in urine specimens from females.
Moncada J, Chow JM, Schachter J.
Journal
of Clinical Microbiology 2003;41:48424843.
Summary:
Question
Does the volume of urine collected affect the sensitivity of nucleic acid
amplification tests for the detection of C. trachomatis in
first-catch urine specimens from women?
Design
This report describes a blinded, head-to-head comparison of three nucleic
acid amplification tests (NAATs), including ligase chain reaction (LCR),
polymerase chain reaction (PCR), and transcription mediated amplification
(TMA), to examine the effect of first-catch urine volume on assay
performance.
Participants
Six hundred fifty-five women seen at an STD clinic in San Francisco, CA,
with or without symptoms, who had not urinated within 2 h prior to
specimen collection, were tested.
Description of Tests and Diagnostic
Standard
Women were given a urine collection cup marked with a black line at the 30
ml level and instructed to collect 30 ml or less of first catch urine. The
specimens were held at 4oC until testing or freezing (TMA only). Specimens
were tested for C. trachomatis within 4 days by LCR (Abbott
Laboratories, Abbott Park, IL) and within 7 days by PCR (Roche Molecular
Systems, Branchburg, NJ). Specimens were held at -70oC for 6
months, then tested for C. trachomatis by TMA (Gen-Probe Inc., San
Diego, CA). Specimens were tested according to the manufacturers'
instructions for each NAAT, but not tested for inhibitors. Specimens were
considered positive for C. trachomatis if at least 2 of the 3 NAAT
results were positive.
Main Outcome Measures
For each NAAT, the prevalence of C. trachomatis and the sensitivity
of detection, stratified by urine volume, were determined.
Main Results
The mean urine volume was 44.4 + 18.1 ml (range = 10 to 90 ml). Two
hundred one (31%) of the 655 women provided 30 ml or less of urine. The
overall sensitivities of LCR, PCR, and TMA were 92.7%, 100%, and 87.8%,
respectively. The performances of the NAATs stratified by urine volume are
shown in the table. For the TMA, C. trachomatis prevalence
decreased significantly as urine volume increased.
Authors' Conclusions
For LCR and TMA, the volume criteria stated
in the product inserts, 15 to 20 ml for LCR and 30 to 50 ml for TMA, might
not be optimal for these tests. For TMA, the rejection of specimens on the
basis of excess volume may be prudent.
Source of funding:
Centers for Disease Control and Prevention, Atlanta, GA
For correspondence: Jeanne Moncada,
Chlamydia Laboratory at SFGH, Department of Laboratory Medicine, Bldg. 30,
Room 416, University of California, San Francisco, CA 94110. E-mail
address: jevemo@itsa.ucsf.edu.
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