THE NEW ZEALAND MEDICAL JOURNAL Vol 116 No 1183 ISSN 1175 8716 NZMJ 10 October 2003, Vol 116 No 1183 Page 1 of 2 URL: http://www.nzma.org.nz/journal/116-1183/630/ © NZMA Negative βhCG: positive ectopic pregnancy Adrian Skinner and Peter Jones A recent case of ectopic pregnancy (EP) following negative urine and ßhCG serum tests highlights potential difficulties involved in diagnosing EP and illustrates the importance of a thorough history and clinical examination augmented by investigative findings. Case report A previously healthy 21-year-old woman presented to the Emergency Department (ED), Auckland Hospital, with a four-hour history of sudden onset, severe, constant, generalised abdominal pain radiating to back and shoulder tip. Significant history was recent unprotected sexual intercourse. She was clinically shocked with a rigid and generally tender abdomen. Vaginal examination was not performed. Urine pregnancy test was negative. Serum β hCG indicated a level <5 IU/l (ie, ‘non-pregnant’). Other investigations included haemoglobin 92 g/l and white cell count 22.12 x 10 9 /l. Electrocardiogram demonstrated sinus tachycardia. Emergency physician abdominal ultrasound revealed significant free pelvic fluid. Impression of ruptured EP resulted in immediate transfer to theatre where the patient underwent laparotomy and right salpingectomy. Surgeons found a ruptured tubal pregnancy in the mid-right fallopian tube. The patient was discharged two days later with uneventful recovery. She re-presented the following day with mild nausea and vaginal bleeding assessed as normal hormonal or acceptable post-salpingectomy bleeding. Gynaecological opinion questioned diagnosis of EP given negative β hCG. Microscopic histology subsequently confirmed presence of EP within the lumen of the fallopian tube, whose wall was markedly attenuated but without rupture in the sections obtained. Discussion Currently utilised pregnancy tests depend on serum or urine detection of hCG ( β subunit confers specificity), a glycoprotein hormone produced by the trophoblast to maintain the corpus luteum. Normal pregnancy concentrations of hCG rise exponentially 10 to 20 days post-ovulation doubling every 48 hours until 8 to 10 weeks and subsequently decreasing to a plateau of around 20% of peak concentrations until term. This increase has been demonstrated among 71% of patients in normal pregnancy but among only 15% of patients with EP, 1 possibly due to non-viable trophoblast or absent production of hCG by the EP. Initial rise to certain maximal levels in EP may be followed by declining levels of hCG. 2 Negative urine and serum hCG tests are reported among 3.1% and 2.6% of EP cases respectively. 3 Serum tests are considered more reliable than urine, 4 with false-negative results among up to 17.5% of urine and 2% of serum tests involving positive EP. 4