Choosing a mouse il-6 elisa kit, a mouse elisa kit for another analyte such as mouse ifn gamma, a mouse igg elisa kit or a human igg elisa kit: why species-specific kits are not interchangeable however similar the target sounds, what an ifn gamma elisa kit measures in an immune readout, and what any elisa test kit owes in its own matrix

Choosing the right kit

1. Match the species exactly, every time. Cytokines are less conserved than their shared names suggest, and a kit raised against the mouse protein generally will not detect the human one. Check the species on the kit against the species of your sample before anything else, because this is the error that wastes a whole plate.
2. For immunoglobulin kits, check the subclass and the specificity. A total immunoglobulin kit and a subclass-specific one answer different questions, and an anti-species reagent may or may not distinguish subclasses. For antibody quantitation in a culture supernatant the subclass usually matters.
3. Match the range to the expected concentration. Immunoglobulin in a supernatant and a cytokine in serum sit orders of magnitude apart. Pick the kit whose standard curve brackets your expected values near its middle, where precision is best, rather than diluting to fit a convenient kit.
4. Qualify in your own matrix. Spike recovery and dilution linearity in the actual sample type. A kit validated in serum used on culture medium, lysate or a tissue extract is unvalidated until you demonstrate the matrix is not interfering.
5. Fix handling before the first plate. Tube type, time to centrifugation, storage temperature and freeze-thaw all move immunoassay results, and several cytokines are released during clotting. Write the protocol down and apply it to every sample in the study.

Running the plate so the numbers survive review

Randomise samples across the plate rather than loading groups in blocks, run standards and samples in duplicate and look at the duplicates rather than only the mean, and put a bridging control on every plate in a multi-plate study.

Fit the curve with the model the kit specifies and treat values read from the flat ends of it as far less certain than the coefficient of variation suggests.

Kit against a custom assay

A kit arrives qualified and costs more per sample. A custom assay from a matched antibody pair is cheaper at volume, takes real development time and gives control of supply, which matters over a multi-year study.

Whichever route, bank one lot of the critical reagents and the standard for the whole study. A new standard lot shifts the entire curve and that shift is indistinguishable from an effect.

Common questions

Can a mouse ELISA kit measure the human protein?

Generally no. These proteins are less conserved than their shared names suggest, and the antibody pair is raised against one species. Check the species on the kit against your sample before ordering.

Total IgG or subclass-specific?

It depends on the question. For quantifying a monoclonal in a supernatant, the subclass-specific kit is usually the right one; for total immunoglobulin in a fluid, the total kit. They are not interchangeable and the standards differ.

Why does my kit saturate?

The range does not match the sample. Immunoglobulin concentrations sit far above cytokine ones, so a kit chosen by target name rather than by expected concentration will either saturate or read below its floor.

Do I have to qualify a commercial kit?

In your own matrix, yes. Spike recovery and dilution linearity take one plate and tell you whether the matrix suppresses or enhances the signal, which no datasheet can tell you about your samples.

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