Table 1.

Performance characteristics of assays for FGF23 measurement

Characteristic	Intact FGF23					C-Terminal FGF23 (Immutopics, Inc.a)
	Kainos Laboratories	Immutopics, Inc.a	EMD Millipore	Shimizu et al. (31)	EMD Millipore
Type/detection	ELISA/colorimetric	ELISA/colorimetric	ELISA/colorimetric	CLIA/chemiluminescent	FIA Luminex/fluorescent	ELISA/colorimetric
Epitope binding region	Unknown	Residues 51–69	Unknown	Unknown	Unknown	Residues 206–222
		Residues 206–222				Residues 225–244
Preferred sample type	Serum	EDTA plasma	EDTA plasma or serum	Serum	EDTA plasma or serum	EDTA plasma
Preanalytical stability issues	No	Yes (13)	No	Not tested	Not tested	No
Sample volumeb (μl)	100	100	100	20	50	100
Functional sensitivity	2 pg/ml	1.5 pg/ml	18 pg/ml	1 pg/ml	37 pg/ml	1.5 RU/ml
Analytical range	2–800 pg/ml	2–2200 pg/ml	18–2400 pg/ml	1–15,000 pg/ml	37–150,000 pg/ml	2–1400 RU/ml
Interassay imprecision (%)	<5	<5	<12	<5	<15	<4
Assay time	3–4 h	3–4 h	3–4 h	20 min	2–16 h	3–4 h
Multiplex capability	No	No	No	No	Yes	No
Independent analytical validation	Yes (11,140)	Yes for first generation kit (11,140)	Yes (11)	No	No	Yes (11,140)
Reference intervalc	No	Yes, for first generation kit (20)	No	No	No	Yes (20,21)
Clinical outcome studiesd	Multiple (36,42,46,50,74,75)	Several (43,141)	None	None	None	Multiple (3–6,55,59,60,142)

FGF23, fibroblast growth factor 23; CLIA, chemiluminescence immunoassay; FIA, fluorescence immunoassay.

^aSecond generation kits.

^bFor duplicate determinations.

^cDefined according to Clinical and Laboratory Standards Institute guidelines (143).

^dDeath or progression to ESRD requiring RRT.