They have been on sale for a few years now, over the counter in some countries and online in others, alongside pregnancy tests and other self-test kits: a lancet, a drop of blood from a fingertip, a cassette, ten minutes, and a line that appears or doesn’t. A doctor might tell you they are “not very reliable, but they can work”. That is a good description. Here is why, and what you can do with one.

What they look for

Home tests look in the blood for anti-transglutaminase antibodies, the same ones as the laboratory blood test, the first step of diagnosis. Some look for IgA alone, others for IgA and IgG. The principle is that of a rapid immunological test: if antibodies are present above a certain level, a line turns colour.

They do not look for the genes (that is a different test), they cannot see the gut, and they do not distinguish celiac disease from non-celiac gluten sensitivity, which produces no antibodies.

What they’re worth

90%or more: sensitivity and specificity in ideal conditions
2 to 3%of people with celiac disease produce no IgA: an IgA test is always negative
10 timesmore IgA deficiency than in the general population

In ideal conditions, someone eating gluten normally, with no IgA deficiency, following the instructions to the letter, manufacturer studies and a few independent ones give sensitivity and specificity around 90 percent or more. That is decent: a positive test has a good chance of matching real disease, a negative one of matching its absence.

In real life, reliability drops, for reasons that have nothing to do with the chemistry of the test:

  • IgA deficiency. Around 2 to 3 percent of people with celiac disease produce no IgA, ten times more than in the general population. In them, a test that looks for IgA is always negative, disease or no disease. The lab measures total IgA to find that out; a home test does not (except those that also look for IgG, which are slightly more robust).
  • Gluten already cut down. Many people buy the test after starting to cut down on gluten, because they feel better. Antibodies fall within a few weeks: the test comes back falsely negative.
  • The drop of blood. Too small, badly placed, the cassette read too early or too late: the line can be missing, or so faint it is misread.
  • Young children. Antibodies are sometimes different before the age of two or three, and home tests have barely been evaluated at that age.

Hence the doctor’s line: not very reliable, but it can work. The test works; it is the conditions that fall short.

What a result means

Positive. This is a serious signal, to be taken seriously. It does not make the diagnosis: it justifies a consultation, a laboratory blood test (anti-transglutaminase IgA plus total IgA), and then, if that confirms, a biopsy. And it does not justify starting the diet: without gluten, the later tests can no longer answer, and you would have to go back on gluten for several weeks. Keep eating gluten until the end of the process.

Negative. The disease is less likely, no more. If symptoms persist, if you have a close relative with celiac disease, if you had already cut down on gluten, or if you do not know whether you have IgA deficiency (nobody knows without having it measured), the laboratory blood test is still needed. A negative home test is not a reason to give up on seeing a doctor.

Unclear (a faint line): treat it as positive, and see a doctor.

Who they help

  • The person who is hesitating about seeing a doctor for vague symptoms, and for whom a positive test will be the trigger to get things moving. That is the most useful use.
  • The person who is eating gluten, has no reason to suspect IgA deficiency, and wants a first pointer before the appointment.

And who they do not help:

  • The person who has already stopped eating gluten: the test can only say “negative”, and that means nothing.
  • The person who already has suggestive symptoms and can get a medical appointment: the laboratory blood test, ordered by a doctor, does better for the same effort.
  • For monitoring diagnosed celiac disease: antibody follow-up is done at the lab, with numerical results, not with a line.

If you are unsure which tests are available where you live, or which are worth doing, your national celiac organisation (Coeliac UK, the Celiac Disease Foundation or Beyond Celiac, Celiac Canada, Coeliac Australia) is a good starting point, and your doctor decides what comes next.

In short

  • Home tests look for anti-transglutaminase antibodies, like the lab; decent reliability in ideal conditions, less so in real life.
  • False negatives are common: IgA deficiency, gluten already cut down, a badly performed test, young children.
  • Positive: a serious signal, see a doctor, laboratory blood test then biopsy, without stopping gluten.
  • Negative: disease less likely, not ruled out; see a doctor if symptoms persist.
  • Useful for prompting a consultation; useless after stopping gluten, and useless for follow-up.

This information does not replace medical advice. A home test does not diagnose celiac disease and is never a reason to start a gluten-free diet on your own: the diagnosis is made with a doctor, through a laboratory blood test and then a biopsy, while you keep eating gluten.