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.
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
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.
Mercodia: Equine Insulin ELISA, Mercodia AB, Uppsala, Sweden
Millipore: Porcine Insulin RIA, Millipore, St. Charles, MO, USA
Discover our other app, the OGT Reference Provider with a dynamic
reference range (90 to 180 min) for the oral glucose test, providing a more practicable test for
insulin dysregulation! → Visit ogt-reference-provider.org!
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.