CT/NG testing detects the presence of two common bacterial sexually transmitted infections (STIs): Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG). This combined test is the current standard method for diagnosing these infections. It is a cornerstone of public health efforts to control the spread of these widespread infections.
Understanding Chlamydia and Gonorrhea
Chlamydia trachomatis and Neisseria gonorrhoeae are bacteria that pose a significant public health concern. Both infections are often asymptomatic, meaning many infected individuals do not experience noticeable symptoms, especially early on. Over 50% of women and a high percentage of men may be asymptomatic, particularly at extragenital sites.
The lack of symptoms allows infections to persist, leading to severe health consequences if left untreated. In women, untreated infection can ascend to the upper reproductive tract, causing Pelvic Inflammatory Disease (PID). PID can result in long-term complications, including chronic pelvic pain, ectopic pregnancy, and infertility. In men, untreated infections can lead to epididymitis, an inflammation of the coiled tube at the back of the testicle.
The Technology Behind CT/NG Testing
The technology powering CT/NG testing is Nucleic Acid Amplification Testing (NAAT). NAAT assays work by detecting and rapidly multiplying small segments of the specific genetic material (DNA or RNA) belonging to the Chlamydia trachomatis and Neisseria gonorrhoeae bacteria. This amplification process creates millions of copies of the target genetic sequence from a minimal starting sample, making the test exceptionally sensitive.
The high sensitivity and specificity of NAAT allow the test to accurately identify an infection even when the bacterial load is very low, such as in asymptomatic cases. Modern NAAT platforms often target multiple unique genetic sequences for each organism, ensuring a highly accurate result and minimizing the chance of a false positive. Because the test looks for the genetic signature rather than a live organism, it can be performed on less invasive and more stable sample types than older culture methods.
Sample Collection and Screening Recommendations
Sample Collection
NAAT technology allows flexibility in sample collection. For men, the preferred sample type is a “first-catch” urine specimen, where the patient collects the initial stream of urine. Patients are instructed not to urinate for at least one hour before collection, as this concentrates the bacteria present in the urethra.
For women, a self-collected vaginal swab is often the preferred specimen type due to its high accuracy and patient acceptability; it is considered as sensitive as a clinician-collected endocervical swab. Testing may also involve swabs from extragenital sites like the rectum or pharynx, depending on the patient’s sexual history, because infections can occur at any site of exposure.
Screening Recommendations
Screening recommendations advise annual testing for all sexually active women aged 24 years and younger. Older women and men who are at increased risk of infection, such as those with new or multiple sexual partners, should also be tested annually. Men who have sex with men are advised to be screened at least annually, often including testing at all exposed sites (urethral, rectal, and pharyngeal).
Interpreting Test Results
CT/NG test results are reported for each organism separately, typically as “Detected” (Positive) or “Not Detected” (Negative). A “Detected” result confirms the presence of the bacteria’s genetic material, indicating an active infection that requires antibiotic treatment to prevent complications and halt transmission.
Following a positive result, immediate steps include treating the patient and notifying sexual partners for testing and treatment. A “Not Detected” result suggests the infection was not present in the collected sample. An “Inconclusive” or “Invalid” result may require a repeat collection. A retest, known as a “test of cure,” may be recommended three to four weeks after treatment in specific cases. Re-screening is generally recommended about three months after treatment for all individuals who tested positive, due to the high risk of reinfection.