## Investigation of Choice for Neisseria gonorrhoeae **Key Point:** NAAT (nucleic acid amplification test) is the gold standard and most sensitive investigation for diagnosis of gonorrhea, particularly in non-invasive specimens like first-void urine. ### Why NAAT is Superior | Investigation | Sensitivity | Specificity | Specimen Type | Advantages | |---|---|---|---|---| | NAAT (PCR/TMA) | 95–99% | >99% | Urine, urethral swab, cervical | Non-invasive, highest sensitivity, detects non-culturable organisms | | Culture (Thayer-Martin) | 85–95% | 100% | Urethral/cervical swab | Gold standard for culture, allows susceptibility testing | | Gram stain | 90–95% (males) | 95% | Urethral exudate | Rapid, presumptive only, poor sensitivity in females | | Oxidase test | N/A | N/A | Culture isolate | Confirmatory only, not diagnostic | | Immunofluorescence | 85–90% | 95% | Urethral swab | Older method, less sensitive than NAAT | **High-Yield:** NAAT is now recommended as first-line by CDC, WHO, and Indian STI guidelines for gonorrhea diagnosis because it: - Detects both viable and non-viable organisms - Works on non-invasive specimens (first-void urine) - Highest sensitivity in both symptomatic and asymptomatic patients - Can be performed on multiple sites simultaneously **Clinical Pearl:** While Gram stain showing gram-negative intracellular diplococci is presumptive in males (>90% specific), it is NOT diagnostic and must be confirmed by culture or NAAT. In females, Gram stain sensitivity is only 50–60%, making NAAT essential. **Warning:** Culture on Thayer-Martin medium, though 100% specific, has lower sensitivity (85–95%) and requires viable organisms. It is still used for susceptibility testing and medicolegal cases, but NAAT is preferred for initial diagnosis. [cite:Park 26e Ch 39]
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