Diagnostic Tests for Epididymitis
The diagnosis of epididymitis requires a Gram-stained smear of urethral exudate, nucleic acid amplification testing for sexually transmitted infections, examination of first-void urine, and syphilis/HIV testing. 1
Key Diagnostic Tests
Gram-stained smear of urethral exudate or intraurethral swab specimen: Used to diagnose urethritis (≥5 polymorphonuclear leukocytes per oil immersion field) and for presumptive diagnosis of gonococcal infection 2, 1
Culture of urethral exudate OR nucleic acid amplification test (NAAT): Either on intraurethral swab or first-void urine for Neisseria gonorrhoeae and Chlamydia trachomatis 2, 1
Examination of first-void uncentrifuged urine: For leukocytes if the urethral Gram stain is negative 2, 1
Culture and Gram-stained smear of uncentrifuged urine: To identify potential enteric organisms, especially in men >35 years 2, 1
Syphilis serology and HIV testing: Recommended for all patients with suspected epididymitis 2, 1
Diagnostic Considerations by Age and Risk Factors
For Men <35 Years
- Focus on STI testing as Chlamydia trachomatis (12.3%) is more common than gonorrhea (3.1%) in this age group 3
- NAAT testing is particularly important as only 50.1% of men diagnosed with epididymitis are tested for gonorrhea and chlamydia during clinical encounters 3
For Men >35 Years
- Greater emphasis on urine culture to identify enteric organisms, with E. coli being the most common pathogen (56%) 3, 4
- Men with positive urine cultures are more likely to have higher urine WBCs, more bacteria, higher leukocyte esterase, and positive urine nitrite 3
Additional Testing in Special Circumstances
Emergency testing for testicular torsion: Consider when onset of pain is sudden, pain is severe, or initial test results don't support urethritis/UTI diagnosis 2, 1
16S ribosomal DNA analysis: Can increase pathogen detection rate by approximately 10% in difficult cases 4
Scrotal MRI with urinary PCR: Consider for suspected tuberculous epididymitis, especially in immunocompromised patients 5
Diagnostic Pitfalls to Avoid
Failure to consider testicular torsion: A surgical emergency that requires immediate specialist consultation; more common in adolescents 2, 1
Inadequate STI testing: STIs are not limited to patients <35 years of age; testing should be considered for all sexually active men 1, 4
Missing rare causes: In cases that don't respond to standard therapy, consider tuberculous or fungal epididymitis (especially in immunocompromised patients), testicular cancer, abscess, or infarction 2, 1
Overlooking viral causes: Although rare (only 1% in studies), viral testing may be considered in cases without bacterial etiology 4
Follow-Up Evaluation
- Improvement should be seen within 3 days of starting treatment 2, 1
- Persistent swelling and tenderness after completing antimicrobial therapy requires comprehensive reevaluation 2, 1
- Consider the differential diagnosis of tumor, abscess, infarction, testicular cancer, and tuberculous or fungal epididymitis in non-responsive cases 2, 1
By following this diagnostic approach, clinicians can accurately identify the cause of epididymitis in approximately 88% of antibiotic-naïve patients and 51% of pretreated patients 4, allowing for appropriate targeted therapy and improved outcomes.