Table 1.

Common problems of cross-reaction and specificity in current immunoassays

Analyte	Cross-reacting compound	Context	Reference
Competitive immunoassays
17OH progesterone	17OH pregnenolone sulfate	Neonates (especially preterm)	Wong, et al. 1992 [182] Makela and Ellis, 1988 [183]
Cortisol	11 desoxy cortisol	11 Hydroxylase defect Metyrapone test	Ward, et al. 2017 [26] Hawley, et al. 2016 [184]
	Prednisone, prednisolone and methylprednisolone	Corticoid therapy	Ward, et al. 2017 [26] Vogeser, et al. 2017 [185]
Estradiol	Estrone sulfate	Hormone replacement therapy (oral administration)	Thomas, et al. 1993 [186]
	Fulvestrant	Breast cancer therapy	Owen, et al. 2019 [11]
	Exemestane metabolites	Breast cancer therapy	Mandic, et al. 2017 [12]
Progesterone	Di-hydroprogesterone	Micronized progesterone therapy	Nahoul, et al. 1987 [187]
Testosterone	Fetal and placental steroids	Females, children	Taieb, et al. 2003 [188] Honour, 2010 [17]
Testosterone	DHEA-S	Females	Warner, et al. 2006 [189]
T3 (either total or free)	Triiodoacetic acid		Piketty, et al. 1996 [190]
DHEAS	Pregnenolone sulphate	Pregnancy	Krasowski, et al. 2014 [191]
Sandwich immunoassays
ACTH 1-39	Fragments, precursor	Paraneoplastic tumors	Raff and Findling, 1989 [20]
Insulin	Pharmacological analogs	Inappropriate injection leading to hypoglycemia	Parfitt, et al. 2015 [22] Giurgea, et al. 2005 [24] Dayaldasani, et al. 2015 [23]
Growth hormone	Pegvisomant	Acromegaly therapy	Paisley, et al. 2007 [18] Manolopoulou, et al. 2012 [19]
	Placental GH	Pregnancy	Dias, et al. 2013 [192]

Abbreviations: ACTH, adrenocorticotropic hormone; DHEAS, dehydroepiandrosterone sulfate.