IGF-1 Z-Score: Historical LMS Method Reference
The Japanese age/sex-specific LMS reference table is NOT included because its reproduction rights and assay correspondence are No patient-specific result can be calculated and no placeholder coefficients are used.
Original method and era
The 2012 Japanese IGF-1 LMS reference used historical immunoradiometric assays. The source distinguished IGF-I Daiichi IRMA (reference method) and Siemens Somatomedin-C-II IRMA; the reported historical correlation was Daiichi = 18.03 + 0.822 × Siemens.
This correlation is restricted to the old assays in the source research. It MUST NOT be applied to current commercial assay measurements without independent validation.
LMS equations (mathematical description only)
Z = [(y/M)^L − 1] / (L × S) for nonzero L, or Z = ln(y/M)/S if L = 0. M is the reference median, not the arithmetic mean. The percentile comes from the standard normal cumulative distribution. Inverse LMS transformation can derive ±2 SD values when a properly licensed, validated model exists.
Required before implementation
Obtain rights to the 2012 sex- and age-specific LMS values, verify model version and assay mapping, assess use of the revised 2023 older-age reference and interpolation between integer ages, and obtain independent professional/clinical sign-off. Age 0–77 in the 2012 source does not authorize unreviewed interpolation or extrapolation.
Illustrative arithmetic, NOT a clinical reference
For synthetic values L = 0, M = 100, S = 0.2, and y = 100, the mathematical Z is 0 and the percentile is 50%. These numbers are not Japanese patient reference data and cannot be used for clinical evaluation.
Sources and review status
Research checked 2026-11-10.