Can a tuboovarian abscess cause a positive human chorionic gonadotropin (hCG) test?

Can a Tuboovarian Abscess Cause a Positive hCG Test?

No, a tuboovarian abscess (TOA) does not directly cause a positive hCG test, but false-positive results have been documented in rare cases, and more importantly, an infected ectopic pregnancy can present as a TOA with a truly positive hCG.

Critical Distinction: True vs False-Positive hCG

False-Positive hCG with TOA (Extremely Rare)

• A single case report documented a false-positive urine β-hCG using modern ELISA technology in a patient with a ruptured TOA, though the mechanism remains unknown 1
• Heterophilic antibodies are the most common cause of false-positive serum β-hCG results, particularly in women exposed to animal antigens, with the key diagnostic clue being positive serum but negative urine β-hCG 2
• When hCG results do not fit the clinical picture, measure hCG on a different assay, as different assays have varying sensitivities and may detect different hCG isoforms 2, 3

Infected Ectopic Pregnancy Mimicking TOA (More Common and Clinically Critical)

• Eight cases of infected ectopic pregnancy presented as unilateral TOA, with all patients having truly positive β-hCG tests preoperatively 4
• These patients presented with abdominal pain, vaginal bleeding following amenorrhea, and fever—symptoms indistinguishable from TOA 4
• In any case of unilateral TOA, infected ectopic pregnancy should be suspected whenever preoperative β-hCG is positive 4

Diagnostic Algorithm When TOA and Positive hCG Coexist

Immediate Steps

1. Obtain both serum and urine β-hCG to identify potential false-positive from heterophilic antibodies, as cross-reactive molecules in blood rarely appear in urine 2, 1
2. Perform transvaginal ultrasound immediately to evaluate for intrauterine pregnancy, adnexal masses, or extraovarian masses, as this is the single best diagnostic modality with 99% sensitivity for ectopic pregnancy 5
3. Assess for extraovarian adnexal mass, which has a positive likelihood ratio of 111 for ectopic pregnancy when no intrauterine pregnancy is identified 5

Interpretation Based on Findings

• If serum positive but urine negative: Suspect false-positive from heterophilic antibodies or assay interference; confirm with different assay 2, 3
• If both serum and urine positive with unilateral adnexal mass: Strongly suspect infected ectopic pregnancy rather than simple TOA 4
• If positive hCG with bilateral TOA and no intrauterine pregnancy: Consider pregnancy of unknown location protocol with serial hCG every 48 hours 5

Clinical Pearls and Pitfalls

Key Warning Signs

• TOA typically presents with lower abdominal pain (predominant symptom), with only a minority showing vaginal symptoms, and approximately half exhibiting fever, nausea, and vomiting 6
• TOA can occur in virginal adolescents through non-sexual routes (bowel translocation, appendiceal spread), making sexual history alone insufficient to exclude the diagnosis 7, 8
• CT has higher sensitivity than ultrasound for TOA diagnosis and can differentiate from gastrointestinal pathology, showing thick-walled fluid density in adnexal location, septations, and potentially gas bubbles 9, 6

Critical Management Principles

• Never initiate treatment for ectopic pregnancy based solely on elevated serum β-hCG without confirming with urine testing and imaging 2
• Approximately 22% of ectopic pregnancies occur at hCG levels <1,000 mIU/mL, so never defer ultrasound based on "low" hCG levels 5
• The traditional discriminatory threshold of 3,000 mIU/mL has virtually no diagnostic utility for predicting ectopic pregnancy (positive likelihood ratio 0.8) 5

Surgical Considerations

• Infected ectopic pregnancies presenting as TOA required unilateral salpingo-oophorectomy in 7 of 8 cases and salpingectomy in one case 4
• Surgical intervention for TOA is more likely needed in patients with bilateral abscesses, large abscesses, and older age 6