Bioassay Research Methodology: Measuring CRH in Pregnancy:

Anumber of researchers have investigated the role of corticotropin-releasing hormone (CRH) in normal and abnormal pregnancies (Lockwood et al., 1996; McLean & Smith, 2001; Siler-Khodr et al., 2003; Smith, Mesiano, & McGrath, 2002; Wadhwa et al., 2004). Associations have been reported between higher levels of CRH and pregnancy adversity, such as preterm birth and hypertension (Hobel, Arora, & Korst, 1999; Ruiz, Fullerton, Brown, & Dudley, 2002; Wadhwa et al., 2004), thus stimulating increased research interest. Although CRH is rarely detectable in the circulation of normal, nonpregnant, and early gestational women, it is present in increasing quantities throughout normal pregnancy, particularly during the second half of gestation (Lockwood et al., 1996). As opposed to normal hypothalamic CRH production outside of pregnancy (in which the CRH is taken up rapidly in the hypophyseal portal blood system, and therefore not seen in the peripheral circulation; Chrousos, 2000), CRH production during pregnancy takes place in the placenta, and the hormone circulates peripherally (McLean & Smith, 2001). Furthermore, placental CRH production is thought to play a prominent role in the normal hormonal, physical, and maturational preparation of the maternal-fetal-placental unit for human labor and birth (Challis, Matthews, Gibb, & Lye, 2000; Norwitz, Robinson, & Challis, 1999). Although there are numerous reports of CRH measurement, they provide insufficient detail regarding the bioassay methodology and rationale and little discussion on maximizing the quality of results. This shortcoming is problematic for researchers who do not possess in-depth laboratory sciences knowledge but who desire to include CRH bioassays in their investigations. Furthermore, this lack of detail and rationale makes it difficult to fully evaluate and compare the results from various studies. As is the case for all bioassays, the quality of CRH measurements can be affected by many variables, such as specimen collection techniques, processing, and storage as well as the actual assay used (i.e., enzyme-linked immunosorbent assay [ELISA] vs. radioimmunoassay [RIA]; Guder, Narayanan, Wisser, & Zawta, 2003). Unexpected results can also be obtained when care has not been taken to adhere to bioassay steps and instructions as provided by the reference labs (Peninsula, 2006). Moreover, CRH measurement is not common in the research laboratory and is extremely rare in the diagnostic lab. Researchers can benefit from expanding their knowledge of bioassay research to the analyte of interest (such as CRH) prior to including these often costly assays in their research studies. Such an approach can enhance the design, conduct, and results of bioassay research as well as the ability to accurately evaluate associations that may exist. The purpose of this article is to address bioassay research methodology, highlighting the issues involved in developing a clinical research protocol specifically for CRH measurement in pregnancy. Accordingly, we conducted a synthesis of laboratory sciences literature specifically focusing on the variables affecting the quality of CRH measurement. Due to the lack of adequate detail and rationale reported in the literature, we also consulted with researchers with expertise in CRH measurement. Using the results of this synthesis and consultation, we developed a proposed laboratory protocol for clinical research.