Explanation

Varicella zoster IgA: what is measured?

The varicella zoster virus (VZV) causes chickenpox and can become active again years later as shingles. Besides IgM and IgG, the immune system can also make IgA antibodies; these are found mainly on mucous membranes and in body fluids. This test measures IgA against the chickenpox virus in blood. Unlike IgM and IgG, the meaning of IgA against this virus has been little studied.

What can it detect?

Contact of the immune system with the chickenpox virus; exactly which situation this belongs to cannot be determined with this test

Result

What does the result mean?

Positive result

IgA antibodies against the chickenpox virus have been found. What this means is hard to say: the meaning of this result has been little studied and there are no agreed threshold values. IgA is sometimes linked to the virus becoming active again, but that link has not been established well enough to draw conclusions from it. A positive result is not proof of an active infection and not a measure of protection; a PCR on blister fluid detects the virus itself, and IgG says something about protection.

Negative result

No IgA antibodies against the chickenpox virus have been found. This too is hard to interpret: a negative result does not rule out an infection at this moment and says nothing about protection. Almost everyone in the Netherlands has had the virus, and the question of whether someone is protected is answered with IgG.

After an abnormal result

A stand-alone IgA result gives no reason for a fixed follow-up. With symptoms, the GP assesses the clinical picture and, if needed, a PCR or an IgG test can follow. Individual cases of chickenpox and shingles are not notifiable.

Reliability

How reliable is the test?

The meaning of IgA against the chickenpox virus has been little studied, and for this test there are no agreed threshold values or known predictive values. An active infection can be shown more reliably with a PCR on blister fluid, and IgG says more about protection. A stand-alone IgA result therefore gives no clear answer to either question.

What can affect the result?

There are no generally accepted cut-off values; tests and results differ greatly between laboratories.
The result does not distinguish between a past infection, a flare-up and an active infection.
On the question of whether someone is protected against chickenpox, IgG says more than IgA.
With a weakened immune system or after administration of immunoglobulins, the result is even harder to interpret.

Who it is for

Who is the test useful for?

Useful for

A stand-alone IgA result says little for any group, because its meaning has been little studied. With symptoms that fit chickenpox or shingles, the appearance of the skin and, if needed, a PCR on blister fluid say more. When planning a pregnancy, during a pregnancy or when working with vulnerable people, the question is whether there is protection, and IgG says more about that.

How common is it?

In the Netherlands, about 95 in 100 people have antibodies against the chickenpox virus; most people have chickenpox as a child. In 2022, GPs registered about 4 in 1000 people with chickenpox, mainly young children. Shingles develops when your own virus becomes active again later and occurs mainly at older age and with a weakened immune system.

The RIVM LCI guideline on chickenpox (Pienter study) and NIVEL

Drawbacks and risks

An abnormal result without a guideline behind it can lead to unnecessary worry and to follow-up testing that adds nothing.
The result can wrongly be read as proof of an active or recurring infection.

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