Chlamydia Antigen

Aka: Chlamydia Antigen, Chlamydia Trachomatis Antigen, Chlamydia Polymerase Chain Reaction, Chlamydia Trachomatis PCR, Chlamydia PCR, Chlamydia Nucleic Acid Amplification Test, Chlamydia Trachomatis NAAT, Chlamydia DNA Probe, Chlamydia Rapid Point-Of-Care Test

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II. Indication

  1. Chlamydia screening in symptomatic and asymptomatic patients

III. Background

  1. Chlamydia Antigen testing has replaced Chlamydia culture
  2. Nucleic Acid Amplification Tests (NAAT, PCR) are the primary tests used in the U.S. for Chlamydia detection

IV. Precautions

  1. Avoid rapid point-of-care Chlamydia tests (very low accuracy, see below)

V. Labs

  1. Chlamydia Nucleic Acid Amplification Test (NAAT, PCR)
    1. Preferred method
  2. Older Methods
    1. Direct Fluorescent Antibody (DFA)
    2. Enzyme Immunoassay (EIA)
  3. Mechanism
    1. Detects both live and dead organisms
    2. Positive test may be seen in recent treatment

VI. Technique

  1. General
    1. Same swab is used to detect both Gonorrhea and Chlamydia
    2. Urogenital samples are not a substitute for anorectal samples
      1. Obtain separate anorectal sample if exposure suspected
  2. Eye Sample
    1. Topical Eye Anesthetic applied
    2. Swab lower and upper lids (inner surface)
  3. Urethral Samples (Males)
    1. Patient should not urinate within 1 hour before test
    2. Insert small Dacron swab 2-4 cm into Urethra
  4. Cervical Samples
    1. Wipe Cervix to remove excess mucus
    2. Insert Dacron swab into endocervix
    3. Rotate swab for 5 to 10 seconds
    4. Withdraw swabs without touching any vaginal surface
  5. Vaginal Sample
    1. Vaginal swabs have similar accuracy to endocervical swabs
    2. In contrast, Pap SmearNAAT liquid cytology has lower Test Sensitivity than endocervical and vaginal samples
      1. Chernesky (2007) J Clin Microbiol 45(8): 2434-8 [PubMed]
  6. Rectal Samples (symptomatic patients)
    1. Insert Dacron swab 3 cm into anal canal
    2. Withdraw swab
    3. Fecal contaminated samples should be redone
  7. Urine Sample
    1. Obtain first catch, "dirty" urine without applying antiseptic before voiding
    2. May miss up to 10% of Cervicitis cases (compared with endocervical swabs)
      1. https://www.cdc.gov/mmwr/preview/mmwrhtml/rr6302a1.htm?s_cid=rr6302a1_w

VII. Efficacy

  1. Chlamydia Nucleic Acid Amplification Tests (NAAT, PCR)
    1. Test Sensitivity: 85.5%
    2. Test Specificity: 99.6%
    3. Cook (2005) Ann Intern Med 142(11):914-25 +PMID: 15941699 [PubMed]
  2. Chlamydia DFA, EIA (older methods, replaced by PCR)
    1. Test Sensitivity: 88-91%
    2. Test Specificity: 97-99%
  3. Chlamydia Rapid Point-Of-Care Tests (avoid, very high False Negative Rate)
    1. Test Sensitivity: 38 to 58%
    2. Test Specificity: 98%
    3. Grillo-Ardila (2020) Cochrane Database Syst Rev (1):CD011708 +PMID: 31995238 [PubMed]

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