Choosing reagents against pathogens and against the response to them: why a spike protein antibody, a spike antibody, an anti spike antibody, an rbd antibody and an ace2 antibody each detect a different part of an interaction and why variant coverage has to be stated, what an hbsag antibody, a cmv antibody, an ebv antibody, hsv1 antibodies, a strongyloides igg antibody, a salmonella antibody, a saccharomyces cerevisiae antibody, an anti lps antibody, an lps antibody and aav antibodies detect as exposure rather than as infection, where a klh antibody, an ovalbumin antibody, a bsa antibody, an anti bsa antibody, a wga antibody, a trypsin antibody and a lysozyme antibody are controls and tools rather than diagnostics, and why an anti peg antibody has become a real consideration for anything formulated

Choosing and interpreting

1. Separate antigen detection from serology. Detecting a pathogen protein indicates the organism is present. Detecting host antibodies indicates exposure, possibly long past, and possibly from vaccination. State which the assay does.
2. Ask about variant coverage. For organisms that change quickly, a reagent raised against one variant may bind others weakly or not at all. Coverage has to be stated and, for anything important, tested against the variants in circulation.
3. Handle samples at the right containment. Clinical and environmental samples carry infectious risk that depends on the agent. Containment level, waste route and vaccination requirements are decided before the first sample arrives.
4. Use immunogen and carrier reagents as controls. Reagents against common carriers and model antigens are experimental tools: they calibrate an assay, check a conjugation and provide a negative. They are not diagnostics and should not be presented as such.
5. Consider anti carrier responses in formulated products. Responses against polymer carriers used in formulation are measurable and clinically relevant, and reagents against them belong in the bioanalytical package for those products.

Exposure, infection and protection are three claims

A serology result establishes exposure. It does not establish current infection, and it does not establish protection, because binding and neutralisation are different properties measured by different assays.

Say which claim the data supports. The distinction is routinely blurred in reporting and it is the source of most misinterpretation in this area.

Research use only means what it says

Reagents in this group are frequently sold for research use and used to answer questions that look clinical. The labelling clause exists precisely for that boundary, and it constrains what may be claimed rather than what may be measured.

Where a result will inform care, the assay and the reagents have to be appropriate to that use. Where it will not, say so plainly in the write up.

Common questions

Does a positive serology result mean current infection?

No. It indicates exposure at some point, which may include vaccination. Current infection is established by detecting the organism or its components, or by a rise in titre between paired samples.

Will a reagent raised against one variant detect others?

Not reliably. Coverage depends on where the epitope sits and how conserved it is, and it has to be stated by the supplier and ideally tested locally against circulating variants.

Why do assays include antibodies against carrier proteins?

As controls and tools: to check a conjugation worked, to provide a negative, or to measure a response against a carrier used in a formulation. They are not diagnostic reagents.

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