Early diagnosis of ectopic pregnancy: can we do it accurately using a biochemical profile?

We wanted to evaluate the utility of seven biochemical markers in the early diagnosis of ectopic pregnancy. Women with pain and bleeding suspicious for ectopic pregnancy were evaluated prospectively. Each woman had a transvaginal sonogram and serum determination of beta-human chorionic gonadotropin (beta-hCG), progesterone, estradiol (E2), creatine phosphokinase (CPK), CA-125, 17-hydroxyprogesterone, and androstenedione. The women were grouped in two ways, and there was considerable overlap between the two groups. One grouping included those with <45 days of amenorrhea, and the other included those whose beta-hCG was <2500 mIU/ml. Each marker was analyzed by univariate and multivariate logistic regression to see which could best distinguish ectopic pregnancies from nonectopic pregnancies. In the group of women with <45 days of amenorrhea, ectopic pregnancies were distinguished by a low progesterone and a high CPK. None of the other biochemical markers were significantly associated with ectopic pregnancy in the multivariate logistic regression analysis. A receiver operating characteristic (ROC) curve was constructed for the CPK/progesterone ratio. As an example of different cut points, a CPK/progesterone ratio >15 was 87% sensitive and 83% specific in the diagnosis of ectopic pregnancy. In the group of women with beta-hCG <2500 mIU/ml, the only biochemical marker found to be significantly associated with ectopic pregnancy was CPK. An ROC curve was constructed for CPK in this group. As an example of different cut points, a CPK >70 had a 78% sensitivity and 81% specificity in the diagnosis of ectopic pregnancy. We conclude that the CPK/progesterone ratio is helpful in those women with <45 days of amenorrhea, and serum CPK levels are helpful in women whose beta-hCG is <2500 mIU/ml. Although serum levels of CPK and the ratio of CPK/progesterone are the most helpful in making the diagnosis of early ectopic pregnancy, they are not good enough to be used alone in clinical practice.