This case highlights a unique anesthetic challenge where a false positive urine pregnancy test led to the cancella-
tion of an elective surgical procedure. While preoperative pregnancy testing is standard, interference from het-
erophilic antibodies—endogenous antibodies that bind to assay antibodies and cause false positive hCG (human
chorionic gonadotropin) results—should be considered to prevent unnecessary delays.
A 40-year-old woman scheduled for elective hamstring rupture repair seven weeks post-injury had a positive urine pregnancy test during preoperative evaluation, prompting surgery cancellation since first-trimester pregnancy is a contraindication for elective anesthesia. However, the patient insisted pregnancy was impossible due to sexual ab- stinence and postmenopausal status from chemotherapy. The anesthesiologist then obtained a quantitative serum hCG test which returned a low positive result (<5), leading to an obstetric consultation. The obstetrician identified heterophilic antibody interference as the probable cause of the false positive. Surgery proceeded without compli- cations.
This case underscores the importance of confirmatory testing for unexpected pregnancy results. Standard anesthe- sia guidelines classify first-trimester pregnancy as a contraindication due to fetal risks. However, recognizing the patient’s low clinical probability, the anesthesiologist appropriately ordered a serum hCG test, revealing hetero- philic antibody interference. One study found nine of 36 peri/postmenopausal women with mildly elevated hCG had elective surgeries canceled. This case highlights the anesthesiologist’s role in critically assessing preoperative findings. Future cases could benefit from confirmatory hCG testing, menstrual/menopausal history, FSH levels, ultrasound, or obstetric consultation to expedite decision-making and minimize patient distress.
A 40-year-old woman scheduled for elective hamstring rupture repair seven weeks post-injury had a positive urine pregnancy test during preoperative evaluation, prompting surgery cancellation since first-trimester pregnancy is a contraindication for elective anesthesia. However, the patient insisted pregnancy was impossible due to sexual ab- stinence and postmenopausal status from chemotherapy. The anesthesiologist then obtained a quantitative serum hCG test which returned a low positive result (<5), leading to an obstetric consultation. The obstetrician identified heterophilic antibody interference as the probable cause of the false positive. Surgery proceeded without compli- cations.
This case underscores the importance of confirmatory testing for unexpected pregnancy results. Standard anesthe- sia guidelines classify first-trimester pregnancy as a contraindication due to fetal risks. However, recognizing the patient’s low clinical probability, the anesthesiologist appropriately ordered a serum hCG test, revealing hetero- philic antibody interference. One study found nine of 36 peri/postmenopausal women with mildly elevated hCG had elective surgeries canceled. This case highlights the anesthesiologist’s role in critically assessing preoperative findings. Future cases could benefit from confirmatory hCG testing, menstrual/menopausal history, FSH levels, ultrasound, or obstetric consultation to expedite decision-making and minimize patient distress.