Method Variability

Investigators are sometimes taken aback after discovering that most clinical laboratory testing is not performed in reference to an absolute standard. That is, a lab value measured by instrument manufacturer A may be slightly different from that by manufacturer B. Each method performs precisely and reproducibly, but the results and reference ranges are slightly different. This is especially true for immunoassay methods. Thus, deciding up front which testing method to use and sticking with it throughout a study is critical. We will be happy to discuss your project and goals and help you decide which method to use when there are multiple options.


Insulin testing has been done using a variety of methods through the years. For most purposes, human insulin is measured on our automated platform. We occasionally still run a radioimmunoassay (RIA) method for researchers that have historically used this method. Mouse insulin assays are run on a different platform.

MethodologySpeciesSample Volume (µL)Measuring Range for Research SpecimensNotes
Cobas e601-
immunoassay (ECLIA
Human3000.2-1000 µU/mL (1.4 – 6945 pmol/L)This method has been standardized using the 1st IRP WHO Reference Standard 66/304 (NIBSC)
RIAHuman50 – 1000.2 – 200 µU/mLCross-Reactivity: Intact Human Proinsulin <0.2%; Des 31, 32 HPI <0.2%; Des 64, 65 HPI 76%


Glucagon testing has been notoriously problematic due to cross-reactivity with similar peptides. We utilize kits from Mercodia as these have the lowest cross-reactivity of any commercially available product for human glucagon.

Sample Type & Storage

Serum or EDTA plasma can be used. Separate as soon as possible and avoid storing at room temperature or refrigerated for longer than 2 hours. Store at -80 oC and avoid freeze-thaw cycles. For samples with very low concentrations of glucagon expected, it may be beneficial to use Becton Dickinson P800 tubes since this can prevent degradation of glucagon.

Analyte (Methodology)SpeciesSample Volume (µL)Measuring RangeNotes
Human251.5 – 130 pmol/L
(5.95 – 453 pg/mL)
No cross-reactivity with glicentin, proglucagon 1-61, or glucagon 3-29
Mouse, Rat, or Porcine102 – 180 pmol/L
(7 – 627 pg/mL)
· 7.0% cross-reactivity with mouse glicentin at 135 pmol/L

· 2.0% cross-reactivity with human/rat/mouse oxyntomodulin at 400 pmol/L

· Calibrated against WHO 1st International reference preparation 69/194