Background:
Urinary symptoms are common in sexually active females, and differentiating urinary tract infections (UTIs) from sexually transmitted infections (STIs) is challenging.

Objective:
To determine 1) if urinary symptoms or UTIs were associated with Chlamydia trachomatis (CT), Neisseria gonorrhoea (NG), or Trichomonas vaginalis (Tv); 2) which findings distinguish UTI from STI.

Method:
A cross sectional sample of sexually-active females was recruited from a teen health center or emergency department. Subjects were interviewed, provided a vaginal swab for Tv culture and a clean catch urine sample for urinalysis (UA), culture, and nucleic acid amplification testing (NAAT) for NG and CT. Data were analyzed using logistic regression (LR) and Classification and regression tree (CART) to identify significant predictor variables.

Result:
Of 301 subjects aged 14-21 years enrolled, 51% reported urinary symptoms, 16.7% had UTI and 33% had STI. Neither urinary symptoms or UTI predicted STI. In the full sample LR, UA leukocyte esterase Ан+1 (LE) significantly predicted STI. In the symptomatic sample, 19.3% had UTI only, 29.7% had STI only, and 6.9% had both. In this group, 62% with sterile pyuria (+LE and -UTI) had STI, +LE predicted NG and Tv, and vaginal symptoms increased the odds of STI without decreasing the odds of UTI. CART analysis of all subjects identified four distinct groups based on UA results: 1) Normal UA: 23.4% STI, 6% UTI. 2) +Nitrites or protein: increased UTI (30%). 3) +LE or blood: increased STI (54.3%). 4) Both +nitrites/protein and +LE/blood: increased STI (36%) and UTI (60%).(p<.001) A decision tree using only UA results correctly classified 65% of subjects.

Conclusion:
UA results can differentiate STI and UTI. In high risk females, sterile pyuria suggests NG or Tv.

Implications:
A single clean catch urine sample allows UA, culture and NAAT for STIs.