What is GC/CT in Laboratory Testing?
GC/CT refers to laboratory testing for Neisseria gonorrhoeae (Gonorrhea/GC) and Chlamydia trachomatis (Chlamydia/CT), the two most common bacterial sexually transmitted infections. This is NOT an abbreviation for gentamicin/clindamycin antibiotics. 1
Laboratory Testing Methods
Nucleic acid amplification tests (NAATs) are the preferred and most sensitive diagnostic method for detecting both GC and CT. 1
FDA-Cleared NAAT Platforms Include:
- Roche Amplicor CT and GC 1
- APTIMA Combo2 (Gen-Probe) 1
- BD ProbeTec (Becton Dickinson) 1
- Xpert CT/NG (Cepheid) 1
Optimal Specimen Sources:
- Women: Vaginal specimens (provider-collected or self-collected) are preferred 1
- Men: First-catch urine specimens are preferred 1
- Men who have sex with men (MSM): Rectal and oropharyngeal testing is recommended, though these require laboratory validation as they are not FDA-cleared 1
Screening Recommendations
Annual CT Screening Should Include: 1
- All sexually active women aged ≤25 years
- All pregnant women
- Older women with risk factors: new/multiple sex partners, partner with STI, inconsistent condom use, previous STI, or exchanging sex for money/drugs
GC Screening (Consider Local Epidemiology): 1
- Sexually active women aged ≤25 years
- Pregnant women
- Similar risk factor criteria as CT screening
Critical Testing Considerations
NAATs provide superior sensitivity compared to culture or hybridization tests while maintaining specificity even in low-prevalence populations. 1
Important Caveats:
- Testing non-genital sites (rectal, oropharyngeal, conjunctival) with NAATs is not FDA-cleared and requires in-house laboratory validation - confirm your laboratory performs these tests before ordering 1
- Culture allows antimicrobial susceptibility testing for GC, which may be important given rising antibiotic resistance 1
- Gram stain in males showing intracellular gram-negative diplococci is 95% specific for GC 1
Test-of-Cure Recommendations:
- Generally NOT recommended unless special circumstances exist (pregnancy, continuing symptoms) 1
- Rescreen high-risk patients within 3-12 months from initial positive test for possible reinfection, as repeat infections increase PID risk 1