Harmonization of IGF1 immunoassays towards a higher-order LC-MS/MS reference anchor
E G W M Lentjes1,2, M S Pratt3, I P Kema3
1Central Diagnostic Laboratory, Utrecht University Medical Center, Utrecht, The Netherlands.
Insights
Harmonizing insulin-like growth factor 1 (IGF1) immunoassays using higher-order reference materials significantly reduces inter-assay variability and improves patient classification. This approach enhances consistency across different testing platforms.
Area of Science:
- Clinical Chemistry
- Biomarker Measurement
- Analytical Chemistry
Background:
- Commercial insulin-like growth factor 1 (IGF1) immunoassays exhibit significant inter-assay variability despite universal calibration.
- This variability leads to inconsistent patient classification and challenges in clinical interpretation.
- Harmonization using a higher-order analytical anchor is proposed to mitigate these issues.
Purpose of the Study:
- To develop and evaluate matrix-matched, commutable serum reference materials (RMs) for harmonizing IGF1 immunoassays.
- To assess the impact of recalibration using a higher-order liquid chromatography-tandem mass spectrometry (LC-MS/MS) anchor on inter-assay variability.
- To construct harmonized, age- and sex-specific reference intervals.
Main Methods:
- Four multi-level, matrix-matched serum RMs were prepared and value-assigned using an LC-MS/MS method.
- Commutability of RMs was assessed across four commercial immunoassays (Cobas, iSYS, Immulite, Liaison).
- Deming regression was used to derive recalibration equations, and the reduction in standard error of estimate (SEE) was the primary endpoint.
Main Results:
- Prior to recalibration, immunoassays showed positive bias up to 60% compared to LC-MS/MS.
- Recalibration using commutable RMs significantly reduced pooled SEE by 37.4% in patient samples and 71.5% in healthy samples.
- Cross-platform dispersion was substantially attenuated, although harmonization effects varied by assay.
Conclusions:
- Matrix-matched, commutable RMs value-assigned by a higher-order LC-MS/MS method effectively reduce inter-assay bias and variability in IGF1 immunoassays.
- Harmonization toward a higher-order analytical anchor is feasible in routine practice.
- This approach provides a foundation for consistent cross-platform interpretation of IGF1 results.
Objective:
Despite the universal calibration of commercial IGF1 immunoassays to WHO IS 02/254, substantial inter-assay variability persists, leading to inconsistent patient classification. Harmonization towards a higher-order analytical anchor may reduce such variability.
Methods:
Four matrix-matched, multi-level serum reference materials (RMs) were prepared from donor serum and value-assigned using an LC-MS/MS method calibrated to WHO IS 02/254. Commutability was assessed according to IFCC recommendations across four immunoassays (Cobas, iSYS, Immulite, Liaison). Deming regression-based recalibration equations derived from commutable RMs were applied to patient samples and healthy donor samples. The primary quantitative endpoint was reduction in standard error of estimate (SEE) relative to the LC-MS/MS method. Age- and sex-specific LC-MS/MS-anchored reference intervals were constructed as a downstream application.
Results:
Prior to recalibration, immunoassays showed positive bias relative to LC-MS/MS of up to 60%. All four RMs were commutable for Liaison and iSYS, whereas the lowest concentration RM was classified as non-commutable for Cobas and Immulite. Recalibration towards the LC-MS/MS anchor resulted in marked alignment towards the identity line and reduced pooled SEE from 7.82 to 4.89 nmol/L (-37.4%) in patient samples and from 7.34 to 2.09 nmol/L (-71.5%) in healthy samples. Although harmonization effects were assay-dependent at the individual platform level, overall cross-platform dispersion was substantially attenuated.
Conclusions:
Matrix-matched, commutable serum RMs value-assigned by a higher-order LC-MS/MS procedure enable substantial reduction of inter-assay bias and variability among IGF1 immunoassays. Harmonization towards a higher-order analytical anchor is achievable in routine practice and provides a robust foundation for consistent cross-platform interpretation.
