Eleanor Kellon, VMD
This study found that insulin testing of samples taken into an EDTA plasma tube (purple top) showed significantly lower levels than serum (red top) or heparin (green top) samples. Best stability when testing is going to be delayed beyond 3 days is heparinized samples.
If you are using Cornell's ACTH/insulin/leptin panel the sample will be EDTA unless the vet also draws a separate serum sample and requests that be used for insulin.
Bottom Line: Use serum or heparin tubes for insulin testing. Varying sample type between tests will not give you accurate results.
Eleanor in PA