App note

Screening Plasma for IgA Deficiency in Under an Hour

A label-free sandwich assay on the P4SPR gives a deficient / normal answer from plasma in about 32 minutes. By ELISA, the same test takes a day.

SystemP4SPR

ApplicationClinical serology, blood banking

SampleHuman plasma

In short: Researchers at Héma-Québec and Université de Montréal built an IgA-deficiency test on the P4SPR that runs from plasma in about 32 minutes on a bench-top instrument. On the clinical samples tested, it gave the same answer as the reference ELISA.

The need

IgA deficiency is the most common immune deficiency: about 0.2% of Canadian blood donors, roughly 1 in 600. Patients who have it can react severely to a transfusion of normal blood, so blood services keep IgA-deficient donors on a registry and hospitals sometimes need to test a patient before transfusing. Today that test is an ELISA run by a central laboratory, with a result after 24 hours or more.

The question for this work: can the same test run at the hospital or the blood drive, within an hour, without a central lab?

How it works on the P4SPR

The assay is an ELISA-style sandwich, read without labels. An anti-IgA antibody on the gold sensor captures IgA from the diluted plasma, and a second anti-IgA antibody then binds to the captured IgA. SPR reads the mass of that second antibody directly, so there is no enzyme, substrate or colour step. Plasma proteins that stick to the surface don't count, because the reading comes from the second antibody only. The gold sensor carries AffiCoat, our low-fouling coating, which keeps most plasma proteins off the surface in the first place.

One run takes five steps on the instrument (Figure 1). The four channels hold two replicates of the sample, a positive reference and a negative reference, so every result comes with its own controls.

The five steps of one run: baseline, plasma sample, wash, second antibody, regeneration — Figure 1. One run on the P4SPR. IgA from the plasma is captured on the sensor, the wash removes everything else, and the second antibody binding to the captured IgA is the reading. A short regeneration step clears the sensor for the next sample.

What the study showed

	Result
Time to result	About 32 min once plasma is separated; under 1 h in total (ELISA: 24 h or more)
Agreement with ELISA	Same deficient / normal call on every clinical plasma sample tested
Sensitivity in plasma	Limit of detection below the 500 ng/mL clinical cut-off

Full method and data: Dubois et al., Transfusion 2024 (reference below).

Why the P4SPR fits this test

What a clinical lab needs	What the P4SPR brings
A result the same day	Real-time readout: about 32 minutes per sample, no overnight incubation
Testing outside a central lab	Portable, bench-top, USB-powered; no moving parts
Confidence in each result	Four channels: sample in duplicate plus positive and negative references in the same run
Works in real samples	AffiCoat low-fouling surface and a second-antibody readout that ignores plasma background
Low cost per test	No labelled antibody or substrate; a sensor can be regenerated and reused for several samples
An assay your team can build	Developed like an ELISA: same antibodies, same logic, no labelling chemistry

Beyond IgA

The design is not specific to IgA. Swap the antibody pair and the same capture-and-confirm format applies to other proteins in blood. As a proof of concept, the same format was set up for ferritin, the iron-storage protein checked in frequent blood donors. Reading the second antibody gave about 2.5 times more signal than reading the captured ferritin directly, and a detection limit about half as low (Figure 2).

Ferritin proof of concept: signal with the second antibody versus direct reading — Figure 2. Ferritin proof of concept (in buffer): the second antibody multiplies the signal across the range. Example recreated from preliminary data; signal shown relative to the direct reading at the top concentration.

If you run an ELISA today and need the answer faster, or closer to the patient, the method in this note is a starting point.

What you need

Item	Source
P4SPR instrument	Affinité Instruments
Gold sensors with AffiCoat	Affinité Instruments
Antibody immobilization (EDC/NHS, ethanolamine)	Standard reagents; see our covalent immobilization protocol
Anti-IgA antibody (capture and detection)	Commercial polyclonal anti-human IgA
Positive and negative reference plasma	Normal plasma and IgA-deficient plasma

Acknowledgements

Thank you to the team at Héma-Québec, and in particular Éric Ducas, Danny Brouard and Jonathan Robidoux, for developing this assay with us, for the clinical samples and the ELISA reference results, and for sharing their ferritin proof of concept.

Reference

C. Dubois, É. Ducas, A. Laforce-Lavoie, J. Robidoux, A. Delorme, L. S. Live, D. Brouard, J.-F. Masson, "A portable surface plasmon resonance (SPR) sensor for the detection of immunoglobulin A in plasma," Transfusion, vol. 64, pp. 881–892, 2024. doi:10.1111/trf.17818 (open access).

Illustrations by Affinité Instruments.