Equine Insulin Converter

Background

The two major equine endocrinopathies pituitary pars intermedia dysfunction (PPID) and the equine metabolic syndrome (EMS) are closely associated with insulin. Therefore, measuring insulin is essential for diagnosing these diseases and preventing laminitis, their most severe clinical consequence. However, many of the available assays measuring insulin provide disparate results, hindering the comparison between measurements and, crucially, with reference ranges and cut-offs obtained using other assays.
Pairs of assays for which a comparison is possible.
Fig. 1 — Pairs of assays for which a comparison is possible.

This web app encapsulates the relationship between many pairs of assays our lab came to compare with each other over the years. An assay-specific insulin measurement can be converted to an approximate value of what would have been obtained with other assays using polynomials. We currently provide conversion for the assay pairs presented in figure 1, but we will try to increase the number of available comparisons in the following months.

To use the app enter an insulin measurement obtained with one of the available assays (in µIU/mL) and press enter or click the ‘convert’.

Please bear in mind that the conversion adds additional uncertainty to the measurement and that every medical decision should take the clinical circumstances into account.

Convert insulin measurements

ADVIA Centaur µIU/mL
Beckman Coulter µIU/mL
Immulite 1000 µIU/mL
Mercodia µIU/mL
Millipore µIU/mL

Assay details

More information

Comparison of different published cut-offs across assays.
Fig. 2 — Comparison of different published cut-offs across assays.

1. Equine Endocrinology Group, Recommendations for the Diagnosis and Treatment of Equine Metabolic Syndrome (EMS), 2016, accessed November 2017.
2. Equine Endocrinology Group, Recommendations for the Diagnosis and Treatment of Equine Metabolic Syndrome (EMS), 2020, accessed August 2021.
3. Warnken T, Delarocque J, Schumacher S, Huber K, Feige K. Retrospective analysis of insulin responses to standard dosed oral glucose tests (OGTs) via naso-gastric tubing towards definition of an objective cut-off value. Acta Veterinaria Scandinavica 2018;60. doi:10.1186/s13028-018-0358-8.
4. Meier AD, de Laat MA, Reiche DB, Pollitt CC, Walsh DM, McGree JM, et al. The oral glucose test predicts laminitis risk in ponies fed a diet high in nonstructural carbohydrates. Domestic Animal Endocrinology 2018;63:1–9. doi:10.1016/j.domaniend.2017.10.008.

As demonstrated in figure 2, insulin cut-offs are not applicable as-is independently of the assay used, warranting the use of assay-specific reference ranges or, in their absence, approximate solutions such as our conversion app.

It is also interesting to note that the lines connecting the converted values to the original cut-offs cross at some point, indicating that the conversion of insulin measurements is not merely proportional to an assay-specific coefficient. The interaction between assays and insulin ought to be investigated using recombinant equine insulin or standardised pooled samples available to all laboratories.

A paper describing the exact methodology to obtain the conversion functions is underway. Briefly, a polynomial function of degree 1 to 2 was estimated using cross-validation and data from samples in which insulin was measured using two or more assays. Each function was visually inspected to preclude overfitting.

Suggested readings:

Julien Delarocque wrote this web app using data provided by Tobias Warnken.