Measurement of urinary free beta-human chorionic gonadotropin by immunoradiometric assay.

An immunoradiometric assay for free beta-human chorionic gonadotropin (F beta hCG) is now available. Measurement of serum F beta hCG has been shown to be valuable for the diagnosis of trophoblastic disease and for screening Down's syndrome pregnancies. Urine specimens may be preferable to blood samples since collection of urine specimens usually are less inconvenient to patients than venipuncture. We have evaluated whether the immunoradiometric assay can be applicable to urine samples. The assay was sensitive and precise. When urine samples were diluted 4-fold or more, the diluted samples gave quantitative values, and recovery of beta hCG added to urine samples was satisfactory. Creatinine corrected urinary F beta hCG levels correlated with serum F beta hCG levels. Thus, the immunoradiometric assay was considered to be applicable to urine samples. Serum F beta hCG to hCG ratio has been reported to be important to distinguish among normal pregnancies, hydatidiform mole and choriocarcinoma. However, urinary F beta hCG to hCG ratio did not significantly correlate with serum F beta hCG to hCG ratio. And therefore, the clinical value of urinary F beta hCG to hCG ratio should be further investigated.