IGF-1 and IGF-1 SDS – fit for purpose?

in European Journal of Endocrinology
Correspondence should be addressed to B E P B Ballieux; Email: b.e.p.b.ballieux@lumc.nl
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    Comparison of the two normative data sets in the groups stratified by age. Two mathematical calculations based on two independent normative data sets were applied to 2828 IGF-1 results analyzed using the IDS-iSYS method to calculate IGF-1 SDS values. SDS 1: calculation based on the normative data of Bidlingmaier (5); SDS2: calculation based on a Dutch cohort (unpublished). The percentage of individuals from different age groups with an IGF-1 SDS <−2 SDS is shown for each normative data set. (A) % males <−2 s.d.; (B) % females <−2 s.d.

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    Simulated results presenting the relationship between analytical and clinical performance specifications for IGF-1 and IGF-1 SDS. (A) Simulation in a male, 8 years old; (B) Simulation in a male, 50 years old Maximal methodological variability expressed as measurement uncertainty (MU) was determined to be ±22% (dashed line) and ±16% (dotted line) in respectively 2017 and 2018 for IGF-1 concentration range from 8.7 to 59.2 nmol/L. The gray area shows clinical performance specifications (CPS) limits of target expressed as ±0.5 s.d. The x-axis represents for a given age/gender group, the possible methodological variability in IGF-1 concentration compared to IGF-1 concentrations at 0 s.d. (), +2 s.d. () and −2 s.d. targets (), respectively. The three lines in both figures fall outside the gray area at different % change from target IGF-1 concentration illustrating non-linear relationship between IGF-1 concentration and SDS. CPS, clinical performance specifications meaning maximal allowable deviation from target SD(S); MU, measurement uncertainty of IGF-1 assay; SD(S), standard deviation (score).

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