A 28-year-old man presents with purulent urethral discharge and dysuria for 3 days. Gram stain of urethral smear shows intracellular gram-negative diplococci. What is the investigation of choice to confirm the diagnosis?

Explanation

## Investigation of Choice for Gonorrhea Confirmation **Key Point:** While Gram stain showing intracellular gram-negative diplococci is presumptive for gonorrhea in symptomatic males, NAAT (nucleic acid amplification test) is the gold standard confirmatory test and has the highest sensitivity and specificity. ### Why NAAT is Superior **High-Yield:** NAAT (PCR, TMA, or SDA) is now the preferred test for gonorrhea diagnosis because it: - Detects both viable and non-viable organisms - Achieves >95% sensitivity and >99% specificity - Can be performed on first-void urine (non-invasive) - Detects asymptomatic infections - Is more sensitive than culture, especially in females and rectal/pharyngeal sites ### Comparison of Diagnostic Methods | Investigation | Sensitivity (Male Urethra) | Specificity | Specimen Type | Clinical Use | |---|---|---|---|---| | Gram stain | 90–95% | 95–98% | Urethral smear | Presumptive diagnosis only | | NAAT | >95% | >99% | Urine, urethral, rectal, pharyngeal | Gold standard confirmatory test | | Culture (Thayer-Martin) | 80–90% | 100% | Urethral/cervical swab | Reference standard but lower sensitivity | | Serology | Variable | Low | Blood | Not recommended for diagnosis | **Clinical Pearl:** In symptomatic males with typical Gram stain findings, treatment can be initiated based on presumptive diagnosis, but NAAT should still be sent for confirmation and to rule out co-infection with Chlamydia trachomatis (which does not show on Gram stain). **Warning:** Culture is no longer recommended as first-line because NAAT is more sensitive, especially in asymptomatic patients and non-urethral sites. Serology has no role in acute gonorrhea diagnosis. ### Algorithm for Gonorrhea Diagnosis ```mermaid flowchart TD A[Suspected gonorrhea]:::outcome --> B{Symptomatic male<br/>with urethral discharge?}:::decision B -->|Yes| C[Gram stain urethral smear]:::action C --> D{Intracellular<br/>gram-negative diplococci?}:::decision D -->|Yes| E[Presumptive diagnosis:<br/>start treatment]:::action D -->|No| F[Send NAAT]:::action E --> G[Send NAAT for confirmation<br/>and chlamydia co-detection]:::action G --> H[NAAT positive]:::outcome B -->|No or female| I[Send NAAT<br/>first-void urine or swab]:::action I --> H ``` [cite:Harrison 21e Ch 137]