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Three Part Question

in [sexually active males presenting to the emergency department with urethral discharge] is [it necessary to wait two hours before taking a urine sample] in order to [make an accurate diagnosis]?

Clinical Scenario

A 26-year-old man presents to the emergency department with a 2-day history of urethral discharge. He had unprotected sex a week previously. You want to take a urine sample from him straight away, but a colleague tells you that the sample must be taken four hours from his last urination. You wonder if there is any evidence for this.

Search Strategy

Medline - 1966 to June week 2 2006
Embase - 1980 to 2006 Week 24
CINAHL - 1982 to June Week 2 2006
[exp Chlamydia trachomatis/ OR exp Gonorrhea/ OR exp Chlamydia Infections/ OR exp Urethritis/ OR exp Neisseria gonorrhoeae/ OR exp Sexually Transmitted Diseases/ OR STD.mp. OR STI.mp. OR (urethra$ adj discharge).mp] AND [exp Urinalysis/ OR urethra$ swab.mp. OR nucleic acid amplification test$.mp. OR NAAT.mp. OR first pass urine.mp. OR urine PCR.mp.] limit to humans and English language and males.

Search Outcome

Altogether 213 papers were identified using Medline, 447 using Embase and 51 using CINAHL. One paper, identified by Medline and Embase, was relevant to the three part question. A further paper was found from a manual search of the references.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Manavi K, Young H. 8th July 2005 UK	1649 men attending the department of GU medicine, Edinburgh for chlamydia screening between Feb 2003 and Jan 2004, whose voiding interval was either less than 2 hours before attending the clinic (n=621), or 2 hours or more (n=1028).	Prospective survey.	pain management	For severe pain, intravenous (IV) administration	Design of study not really appropriate for objectives. Not a randomised controlled trial. Does not take into account the fact that diagnosis could be missed by test in those with a voiding interval of less than 2 hours. Assumes rate of infection will be roughly the same in both groups. May be differences between groups as chlamydia causes urinary frequency, so those with void time of less than 2 hours may have higher rate of chlamydia. Takes participants word for time of last voiding. This could be inaccurate and so flaw study.
			Incidence of chlamydia	17.1% voiding interval<2 hours v. 16.5% voiding interval 2 hours or more (p=0.779)
Sellors J, Chernsky M, Pickard L et al. 1993 Canada	428 men attending a STD clinic between June 1990 to October 1991	Prospective Survey	Incidence of Chlamydia	8.9%	Not a randomised controlled trial Aims of study not clearly stated Results not displayed clearly, or in sufficent detail, with little information on results of statistical tests. Urethral swab used as gold-standard
			sensitivity of testing FVU compared to urethral swabs	81.6%
			Association between time since previous voiding and test sensitivity	not statistically significant (no figures given)
			Sensitivity of EIA performed on FVU, if FVU collected before or after swab	82.3% v. 75.0% respectively (p=1.00)

Comment(s)

The issue of how long you should wait before taking a urine sample in men with a suspected STD is a tricky one. Different testing kits give different recommendations (for example the Roche Cobas Amplicor CT/NG test recommends a voiding interval of 2 hours or more), but little evidence has been shown to back these recommendations up. Both papers cited suggest that the length of voiding interval is not important. However, both papers have several major flaws, and do not give the best level of evidence. There is also no mention of the effect of voiding interval on testing for Neisseria gonorrhoeae. It seems that further research is required in this area in order to give good evidence based recommendations.

Clinical Bottom Line

It does not appear to be necessary to have a voiding interval before testing for Chlamydia trachomatis. There is no evidence for testing for Neisseria gonorrhoeae. Due to lack of evidence, local guidance should be followed.

References

1. Manavi K, Young H The significance of voiding interval before testing urine samples for Chlamydia trachomatis in men Sexually Transmitted Infections 2006;82:34-36
2. Sellors J, Chernsky M, Pickard L et al. Effect of time elapsed since previous voiding on the detection of Chlamydia trachomatis antigen in urine European journal of clinical microbiology & infectious diseases 1993;12:285-9