Gonorrhea laboratory tests

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Mehrsefat, M.D. [2]

Laboratory tests

Several laboratory tests are available to diagnose gonorrhea. A doctor or nurse can obtain a sample for testing from the parts of the body likely to be infected (cervix, urethra, rectum, or throat) and send the sample to a laboratory for analysis. Gonorrhea that is present in the cervix or urethra can be diagnosed in a laboratory by testing a urine sample.

Gram stain

• Gram stain is highly sensitive and specific in men with symptomatic urethritis. However, because of lower sensitivity, detection of infection using Gram stain of endocervical, pharyngeal, and rectal specimens also is insufficient and is not recommended.
• In symptomatic men, polymorphonuclear leukocytes (PMNs) with intracellular Gram-negative diplococci can be considered diagnostic for infection with Neisseria gonorrhea.
• Common anatomic sites for taking samples include:
  • Cervical Gram stain in women
  • urethral discharge Gram stain in men
  • Synovial fluid Gram stain

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  Neisseria gonorrhoeae in cervical smear using the Gram-stain

• 

  Urethral discharge for Neisseria gonorrhea revealed Gram-negative intracellular rods

• 

  Intracellular Gram-negative diplococcal

Cultures

Culture is the historical standard for detection of Neisseria gonorrhea.

• Culture test dvantages over non-culture tests include:Papp, John R., et al. "Recommendations for the laboratory-based detection of Chlamydia trachomatis and Neisseria gonorrhoeae—2014." MMWR. Recommendations and reports: Morbidity and mortality weekly report. Recommendations and reports/Centers for Disease Control 63 (2014): 1.http://www.cdc.gov/mmwr/preview/mmwrhtml/rr6302a1.htm</ref>
  • Low cost
  • Suitable for a variety of specimen sites
  • Antimicrobial susceptibility testing can be performed

Thayer-Martin medium is one example of a medium used for Neisseria gonorrhoeae culture. Cultures can provide a preliminary diagnosis often within 24 hours and a confirmed diagnosis within 72 hours.

• Common anatomic sites for taking samples include:
  • Vaginal and cervical culture
  • Urethral discharge culture in men
  • Throat swab culture
  • Rectal culture
  • Synovial fluid culture
  • Blood cultures

Nucleic Acid Amplification Tests (NAATs)

NAATs are the most sensitive test to detect infections. Amplified tests include:

• Polymerase chain reaction (PCR)
• Transcription-mediated amplification (TMA)
• Strand displacement amplification (SDA)

NAAT is FDA-cleared for:

• Endocervical swabs from women
• Urethral swabs from men
• Urine specimens from both males and females
• Vaginal swabs (some NAATs are clear)

NAAT is not FDA-cleared for detection of rectal, oropharyngeal, and conjunctival gonococcal infection.

• Some laboratories have met CLIA regulatory requirements and established performance specifications for using NAAT with rectal and oropharyngeal swab specimens that can inform clinical management.
• Antimicrobial susceptibility cannot be determined with these tests. However, the same specimen can be evaluated for Chlamydia trachomatis.
• There is a concern about cross-reactivity with other Neisseria species when used at the oropharyngeal site.

Non-amplified tests

Non-amplified tests used for Neisseria gonorrhea include:

• DNA probe (e.g., Gen-Probe PACE 2 and Digene Hybrid Capture II)

Antimicrobial susceptibility cannot be determined with these tests. However, the same specimen can be evaluated for Chlamydia trachomatis.

Sexual Abuse/Sexual Assault Diagnosis

In cases of suspected sexual abuse or assault, the legal standard is culture. All positive specimens should be retained for additional testing.

• In adults, NAATs are preferred for the diagnostic evaluation of sexual assault regardless of penetration.
• In children, data on use of NAATs for detection of N. gonorrhoeae are limited, and consultation with an expert is necessary before using NAATs in this context to minimize the possibility of cross-reaction with nongonococcal Neisseria species.

Gallery

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  Image depicts the morphologic appearance of Neisseria gonorrhoeae colonies after having grown for a period of 24 hours on GC media base agar supplemented with IsoVitaleX (50X mag). GC media base agar is used in the isolation of N. gonorrhoeae bacteria, and is often used in conjunction with various antibiotics, in order to determine N. gonorrhoeae antimicrobial sensitivity/selectivity. From Public Health Image Library (PHIL).

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  Photomicrograph of Neisseria gonorrhoeae in cervical smear using the Gram-stain technique. From Public Health Image Library (PHIL).

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  Urethral discharge for Neisseria gonorrhea revealed Gram-negative intracellular rods, NOT diplococci. From Public Health Image Library (PHIL).

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  Photomicrograph reveals presence of intracellular Gram-negative, Neisseria gonorrhoeae diplococcal bacteria. From Public Health Image Library (PHIL).

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  This Gram-stained photomicrograph revealed the presence of what was termed as “deceptive” extracellular diplococcal bacteria. From Public Health Image Library (PHIL).

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  Photomicrograph reveals Gram-negative rods, and Gram-negative cocci, which were determined to be Haemophilus influenzae, and non-meningococcal Neisseria sp. organisms respectively. From Public Health Image Library (PHIL).

• 

  Photomicrograph (1000X mag) reveals Gram-negative rods, and Gram-negative cocci, which were determined to be Haemophilus influenzae, and non-meningococcal Neisseria sp. organisms respectively. From Public Health Image Library (PHIL).