Two-center clinical evaluation of a new automated fluorometric immunoassay for the quantitative analysis of total eta-human chorionic gonadotropin Hassan M. E. Azzazy a , Liana Frances Romero b , Lee Hall b , Doris Ruttle c , Robert H. Christenson a, * a Departments of Pathology and Medical and Research Technology, University of Maryland School of Medicine, Baltimore, Maryland 21201 b Dade Behring, Newark, Delaware c Methodist Medical Center of Illinois, Peoria, Illinois Received 10 February 2003; received in revised form 31 July 2003; accepted 5 August 2003 Abstract Objectives: This study evaluated the quantitative total hCG assay on the StratusCS point-of-care instrument at two medical centers. Design and methods: Analytical sensitivity, linearity, within-run and total imprecision, interferences, dilution recovery, method compar- ison (Dimension® RxL), comparison of matched heparinized whole blood and plasma samples, and determination of the normal reference interval were studied. Results: Analytical sensitivity was 0.5 IU/L. The assay’s linear range was 0 to 1250 IU/L; the clinical reportable range was up to 50,000 IU/L. Within-run imprecision (CV) at both low (20 IU/L) and elevated (760 IU/L) hCG concentrations were 4%. Total imprecision for three QC levels and two pools were 4%. Method comparison showed Stratus CS hCG = 0.98 0.01* Dimension RxL hCG -0.11 2.69 (n = 136; r = 0.996; Sy/x = 27.7). Matched heparinized whole blood/plasma sample-comparison showed: whole blood = 1.05*Plasma + 0.37 1.29 (n = 41; r = 1.000; Sy/x = 7.57). Mean dilution recovery was 99% (range: 95% to 103%). None of the 52 drugs tested, lipemia, icterus, hemolysis, LH, FSH, TSH, hGH or prolactin represented a significant interference with the assay. Reference intervals were 0.5 IU/L for males (n = 123) and 3.0 IU/L for nonpregnant females (n = 120). Conclusions: The StratusCS hCG test offers the advantage of quantitative measurement of total hCG in whole blood at the point of care and is suitable for clinical use. © 2003 The Canadian Society of Clinical Chemists. All rights reserved. Keywords: Total beta human chorionic gonadotropin; Fluorometric immunoassay; Pregnancy monitoring; Stratus CS; quantitative 1. Introduction Human chorionic gonadotropin (hCG) is a member of a group of closely related glycoprotein hormones [1]. Three members of this group- luteinizing hormone (LH), follicle- stimulating hormone (FSH) and hCG- regulate aspects of reproduction while thyroid-stimulating hormone (TSH) reg- ulates metabolism. LH, FSH and TSH are produced within the pituitary gland while hCG is produced by the placenta. Evidence however indicates that the pituitary also produces a small quantity of hCG [2]. hCG is a heterodimeric sialoglycoprotein hormone pro- duced by the placenta soon after implantation of the fertil- ized ovum into the uterine wall [3,4]. Physiologically, it is involved in the maintenance of the corpus luteum and sup- port of the endometrium during pregnancy. Similar to an- terior pituitary glycoprotein hormones, LH, FSH, and TSH, the bioactive form of hCG is a dimer consisting of an and subunits, joined noncovalently. The -subunit of hCG is coded by a different gene which discriminates hCG from the other glycoprotein hormones. It is composed of 145 amino acids and contains 6 intra-disulfide bridges and O- and N-linked oligosaccharide side chains [1]. hCG circulates primarily as an intact, dimeric molecule in the plasma of women who have an uncomplicated preg- nancy. hCG is found naturally in blood and urine in differ- * Corresponding author. Fax: +410-328-5880. E-mail address: rchristenson@umm.edu (R. Christenson). Clinical Biochemistry 36 (2003) 523–528 0009-9120/03/$ – see front matter © 2003 The Canadian Society of Clinical Chemists. All rights reserved. doi:10.1016/j.clinbiochem.2003.08.003