Gram Stain Findings in Gonorrhea
On Gram stain for gonorrhea, you will see Gram-negative intracellular diplococci within polymorphonuclear leukocytes (PMNs), appearing as pairs of kidney bean or coffee bean-shaped bacteria inside white blood cells. 1
Microscopic Appearance
The characteristic finding is Gram-negative diplococci with the following features:
- Morphology: Pairs of bacteria arranged side-by-side, classically described as "kidney bean-shaped" or "coffee bean-shaped" with adjacent concave sides 2, 3
- Location: Intracellular - found inside polymorphonuclear leukocytes (neutrophils) 1
- Staining: Gram-negative (pink/red color after Gram staining) 1
Clinical Utility by Specimen Type
Male Urethral Specimens (Symptomatic Men)
Gram stain is highly accurate and can be diagnostic in symptomatic men with urethral discharge:
- Sensitivity >95% and specificity >99% when intracellular Gram-negative diplococci are present 1, 4
- The presence of polymorphonuclear leukocytes with intracellular Gram-negative diplococci is considered diagnostic for N. gonorrhoeae infection in symptomatic men 1
- However, a negative Gram stain does NOT rule out infection in asymptomatic men due to lower sensitivity 1, 4
Female Endocervical Specimens
Gram stain is NOT recommended for diagnosing gonorrhea in women:
- Gram stain of endocervical specimens has insufficient sensitivity to detect infection 1, 4
- The CDC explicitly states that Gram stain of endocervical specimens is not sufficient and therefore not recommended 1
- Research confirms poor accuracy with kappa values ranging from -0.09 to 0.24 in endocervical smears 5
Extragenital Sites (Pharynx, Rectum)
Gram stain is NOT recommended for pharyngeal or rectal specimens:
- These sites lack sufficient sensitivity and specificity for diagnosis 1
- Culture or validated NAATs are the preferred diagnostic methods for extragenital sites 1, 4
Important Caveats and Pitfalls
Mimicking Organisms
Other bacteria can appear similar to N. gonorrhoeae on Gram stain:
- Moraxella catarrhalis and other Neisseria species (including N. meningitidis) can appear as Gram-negative diplococci 1
- Confirmatory testing with culture or NAAT is essential for definitive diagnosis due to public health and treatment implications 1
When Gram Stain Should NOT Be Used Alone
- Asymptomatic men: Lower sensitivity makes negative results unreliable 1, 4
- All women: Regardless of symptoms or specimen site 1, 4
- Pharyngeal and rectal specimens: Insufficient diagnostic accuracy 1
- Child sexual abuse cases: Non-culture tests including Gram stain should not be used without confirmation 4
Current Diagnostic Recommendations
NAATs are now the preferred diagnostic method for genitourinary gonorrhea with sensitivity >95% and specificity >99%, and can detect infections that Gram stain would miss 4. Gram stain remains useful primarily as a rapid point-of-care test in symptomatic men with urethral discharge where immediate presumptive treatment decisions are needed 1, 4.