URINE HCG BETA-SUBUNIT CORE FRAGMENT, A SENSITIVE TEST FOR ECTOPIC PREGNANCY

hCG is a glycoprotein hormone composed of 2 dissimilar subunits, alpha and beta, joined non-covalently. hCG and its free beta-subunit are th e principal hCG beta immunoreactivities in pregnancy serum samples, an d the same plus beta-core fragment (beta-subunit residues 6-40 disulfi de-linked to residues 55-92) in urine samples. Ectopic or tubal pregna ncy is difficult to diagnose in emergency rooms. With the objective of finding better hCG-related assays for differentiating tubal and norma l pregnancies, we tested 2 hCG, 1 free beta-subunit and 2 beta-core fr agment immunoassays. Twelve urine samples were collected in the emerge ncy room from women later shown by surgery to have tubal pregnancy. Al l were 38 to 80 days since last period. A further 36 urine samples wer e collected from the same period from those with normal intrauterine p regnancies. Using the 2 hCG assays the median level in tubal pregnancy samples was 1/38th and 1/48th of normal pregnancy concentrations. Wit h the free beta-subunit assay tubal pregnancy levels were 1/28th of no rmal levels. Using 2 beta-core fragment assays (Ciba-Triton UGP kit an d B204-FBT11 scavenger test), however, tubal levels were most differen t from intrauterine pregnancy, 1/149th and 1/800th of normal levels. A cut-off level of 100 mu g/L was considered for the B204-F1BT11 beta-c ore fragment test, at which a predictive value of > 98% was suggested for ectopic pregnancy. In an additional patient, levels were measured 15 days prior to the diagnosis of tubal pregnancy. At this time, resul ts from the 2 hCG tests were 1/97th and 1/126th, from the free beta-su bunit test was 1/8th and the 2 beta-core assays were 1/413th and 1/240 th of median normal intrauterine pregnancy levels. While hCG levels ar e reduced in tubal pregnancy, beta-core fragment are reduced much furt her. beta-core fragment measurements may offer a major improvement ove r hCG in diagnosing tubal pregnancy in the Emergency Room, and in scre ening for this life threatening disease.