Biological variation of intact fibroblast growth factor 23 measured on a fully automated chemiluminescent platform

Fibroblast growth factor 23 (FGF23), a potent regulator of phosphate and vitamin D metabolism, is a new biomarker of kidney, bone and cardiovascular disorders. The aim of this study was to assess the biological variation of intact fibroblast growth factor 23 (iFGF23).

The within-subject (CV_I) and between-subject (CV_G) biological variations were assessed in 14 healthy volunteers in a six-week protocol (seven samples). Imprecision (CV_A) was assessed by duplicate measurements and the EP15-A2 protocol. Intact FGF23 was measured using a fully automated chemiluminescent assay (Liaison XL, DiaSorin S.p.A., Saluggia, Italy). Two methods with different sensitivities to non-Gaussian distribution were used to estimate the CV_I, SD ANOVA and CV ANOVA methods. We calculated the index of individuality (II) and reference change values.

Depending on the statistical method used, the CV_I and CV_A were 14.2 and 3.7% (SD ANOVA) or 12.5 and 3.9% (CV ANOVA), respectively. The corresponding reference change values were 40.5 and 36.4%, respectively. The CV_G was 13.4% (SD ANOVA was the only option), and the total imprecision (EP15-A2) was less than 7%.

The measurement of iFGF23 demonstrated a CV_A less than 4% during the experimental estimation of biological variation. The total imprecision was less than 7% in the EP15-A2 experiment. The CV_I values of iFGF23 in healthy persons were 14.2 (SD ANOVA) and 12.5% (CV ANOVA), respectively. The CV_G was 13.4%, and the resulting index of individuality was 1.06. The reference change value was less than 41%. The availability of this automated assay for iFGF23 with well-characterized biological variation data delivers opportunities for improved availability and application of this assay clinically.