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Experiences with Chlamydia testing using the BD ProbeTecET and BD Viper focusing on inhibition in urine samples

Abstract number: 902_p719

Lisby G.

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Objectives:

On June 1, 2003 our laboratory changed the Chlamydia trachomatis (CT) testing platform from PCR/EIA to real-time strand displacement amplification (SDA) using the BD Viper sample preparation robot and two BD ProbeTecETs. The lab performs 70 000 CT analysis per year. The wet swab for cervix and urethra, and urine testing for men was introduced. We evaluated the inhibition rate in different specimen types and analysed the effect of washing urine samples prior to testing.

Methods:

We evaluated the first 6 months of using SDA (33 000 samples). Information was obtained from our LIS. A patient was only included once and a positive test result had priority over negative results. We calculated changes in gender sampling, sampling site, age-specific positive sample rate and age-specific percentage of women tested in Copenhagen. After washing 91 negative urine samples and 90 positive urine samples were retested without the washing step.

Results:

The average positive sample rate increased from 4.4 (EIA) to 6.4% (SDA). The age-specific positive rate for women increased for all ages over 18 years. The positive rate from female urine n = 130 was 5.4% and from male urine, n = 2220, 15%. CT samples from men were increased by 53% and positive rate from 12.5–13.7%. Inhibition was seen in 0.7% from cervix, 0.16% from female urethra, 0% from female urine, 0.24% from male urethra and 0.14% from male urine.

Reportable results were obtained from 80/91 (88%) unwashed urines that were negative after washing. 11/91 had inhibition (12%) and one of 80 was borderline positive.

Reportable results were obtained from 88/90 (97.8%) unwashed urines that were positive after washing. Two of 90 had inhibition (2.2%) and three of 88 were negative.

Conclusion:

The positive sample rate was increased by 45% in women and 9.6% in men with male sampling increasing by 53%. Inhibition was only seen in 0.46% of samples, primarily from cervical samples. Washing of urine samples removes virtually all inhibition. Inhibition rate for unwashed urines was significantly higher in negative urines than positive urines P = 0.02. Omitting the washing step (with a CT prevalence of 15%) will reduce the time spent on washing by about 66%. This will delay laboratory answers on the inhibited samples by one day due to washing and re-analysis of approximately 10% of the urine samples.

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Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Subject:
Location: Oxford, UK
Presentation type:
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