A 28-year-old woman presents to the clinic 6 weeks after insertion of a copper intrauterine device (Cu-IUD) with complaints of persistent lower abdominal pain, vaginal discharge, and fever (38.2°C). She denies recent unprotected intercourse. Which investigation is most appropriate to confirm the suspected diagnosis of acute pelvic inflammatory disease (PID) and assess for IUD-related complications?

Explanation

## Investigation of Choice for Suspected PID Post-IUD Insertion ### Clinical Scenario Post-IUD insertion PID is a rare but serious complication (incidence ~0.5–1.4 per 1000 insertions). Early diagnosis and differentiation from other causes of pain are critical. ### Why Transvaginal Ultrasound with Doppler + Endocervical NAAT? **Key Point:** Transvaginal ultrasound is the imaging modality of choice for PID because it has superior sensitivity (90–95%) for detecting adnexal pathology, free fluid, and tubo-ovarian complexes compared to transabdominal ultrasound or clinical examination alone. **High-Yield:** Doppler assessment evaluates: - Increased vascularity (hyperemia) in inflamed adnexa - Presence of free pelvic fluid (suggests peritonitis) - Tubo-ovarian abscess formation **Key Point:** Endocervical NAAT (PCR for *Chlamydia trachomatis* and *Neisseria gonorrhoeae*) is the gold standard for microbiologic diagnosis of PID; sensitivity >95% and specificity >99%. ### Diagnostic Approach Table | Investigation | Diagnostic Value | Sensitivity | Specificity | Role in PID | |---|---|---|---|---| | Transvaginal ultrasound + Doppler | Morphology + vascularity | 90–95% | 85–90% | Confirms diagnosis, assesses severity | | Endocervical NAAT | Microbiology | >95% | >99% | Identifies causative organisms | | Abdominal X-ray | IUD position only | Low | Moderate | Does not diagnose PID | | CBC + ESR | Nonspecific inflammation | Low specificity | Low specificity | Supportive only, not diagnostic | | Urine culture | Urinary pathogens | N/A | N/A | Irrelevant to PID diagnosis | **Mnemonic:** **PELVIC** — **P**elvic ultrasound (transvaginal), **E**ndocervical swab (NAAT), **L**aboratory markers (CRP, ESR), **V**iral/bacterial serology, **I**maging (Doppler), **C**linical assessment. ### Clinical Pearl In post-IUD insertion PID, transvaginal ultrasound also helps exclude IUD perforation, malposition, or expulsion — complications that may coexist with infection and require device removal. ### Guideline Alignment [cite:Park 26e Ch 7] and CDC STI guidelines recommend endocervical NAAT as the diagnostic standard for PID, combined with imaging (transvaginal ultrasound) for severity assessment and exclusion of complications.