| SPINA-GBeta | |
| Purpose: | Medical diagnosis, research |
| Test Of: | Pancreatic beta cell function |
| Reference Range: | 0.64–3.73 pmol/s |
| Calculator: | https://doi.org/10.5281/zenodo.7479856 |
SPINA-GBeta is a calculated biomarker for pancreatic beta cell function.[1] It represents the maximum amount of insulin that beta cells can produce per time-unit (e.g. in one second).
The index is derived from a mathematical model of insulin-glucose homeostasis.[2] For diagnostic purposes, it is calculated from fasting insulin and glucose concentrations with:
{\widehat{G}}\beta=
| [I](infty)({D | |
| \beta |
+\left[G\right](infty))}{{G}3[G](infty)}
[''I''](∞): Fasting Insulin plasma concentration (μU/mL)
[''G''](∞): Fasting blood glucose concentration (mg/dL)
Dβ: EC50 for glucose at beta cells (7 mmol/L)
G3: Parameter for pharmacokinetics (58,8 s/L)
SPINA-GBeta significantly correlates with the M value in glucose clamp studies and (better than HOMA-Beta) with the two-hour value in oral glucose tolerance testing (OGTT), glucose rise in OGTT, subscapular skinfold, truncal fat content and the HbA1c fraction.[1]
It has the additional advantage that it circumvents the HOMA-blind zone, which renders the calculation of HOMA-Beta impossible if the fasting glucose concentration is 3.5 mmol/L (63 mg/dL) or below.[3] Unlike HOMA-Beta, SPINA-Beta can be sensibly calculated in the whole range of measurements.[1]
In repeated measurements, SPINA-GBeta had higher retest reliability than HOMA-Beta, a measurement for beta cell function from the homeostasis model assessment.[1] [4]
In the FAST study, an observational case-control sequencing study including 300 persons from Germany, SPINA-GBeta differed more clearly between subjects with and without diabetes than the corresponding HOMA-Beta index.[4]
Together with the reconstructed insulin receptor gain (SPINA-GR), SPINA-GBeta provides the foundation for the definition of a fasting based disposition index of insulin-glucose homeostasis (SPINA-DI).[4]
In combination with SPINA-GR and whole-exome sequencing, calculating SPINA-GBeta helped to identify a new form of monogenetic diabetes (MODY) that is characterised by primary insulin resistance and results from a missense variant of the type 2 ryanodine receptor (RyR2) gene (p.N2291D).[5]
In several populations, SPINA-GBeta correlated with the area under the glucose curve and 2-hour concentrations of glucose, insulin and proinsulin in oral glucose tolerance testing, concentrations of free fatty acids, ghrelin and adiponectin, and the HbA1c fraction.[4]