When Should You Get Tested for Nail Fungus?

Deciding to test a nail is one thing; knowing when to test is another. Test at the right moment and the result gives you and your healthcare provider a clear way forward. Test at the wrong moment, such as right after finishing an antifungal course, and the result can be harder to interpret. Here's a practical guide to timing.

If you're still deciding whether testing is worthwhile at all, start with why you should test before treating nail fungus.

Good times to test

1. When you first notice a change that isn't going away

A new white or yellow patch, a nail that's starting to thicken, or crumbling at the tip are all reasonable reasons to test, especially if the change is spreading over a few weeks or months. The AAD notes that a cure is more likely with early treatment, and finding out early means you can act sooner. Our article on early signs and stages of toenail fungus describes what to look for.

2. Before starting any treatment

This is the single most useful time to test. Before you commit to months of nail paint, tablets or a laser package, confirm that fungus is actually present. Many discoloured nails turn out to be caused by trauma or psoriasis instead. If you're about to see a healthcare provider, a result can make the appointment more productive.

3. When treatment doesn't seem to be working

If you've been using a treatment as directed for several months and see no clear, healthy nail growing in at the base, it's worth asking whether the nail was fungal to begin with. A test can help you and your provider decide whether to keep going, change approach or look for another cause.

4. When the nail looks different from your usual pattern

If you have psoriasis or an old nail injury and one nail suddenly changes, fungus may have joined in. Both are known risk factors for fungal infection.

5. When someone at home has nail fungus

Nail fungus can spread within a household. If a family member has a confirmed infection and you notice changes in your own nails, testing can tell you whether you need treatment too (see is toenail fungus contagious?). Each person needs their own sample.

When it's better to wait

Right after an injury

If you've just stubbed or crushed a toe and the nail is red, purple or black, that's usually blood under the nail rather than fungus. Give it time to grow out, and see a healthcare provider promptly if there's severe pain, a possible fracture, or signs of infection. Read toenail fungus or a bruise? for details.

During or soon after antifungal treatment

qPCR testing detects fungal DNA, and DNA can remain in the nail after fungi have died. That means a test taken during treatment or soon after finishing may still detect DNA even if treatment has worked. If you want to check whether treatment succeeded, ask your healthcare provider about the right timing. Often it makes sense to wait until a good amount of new nail has grown out.

Recent topical products on the nail

Remove any nail polish and wash and dry your foot before collecting your sample. If you've been using a medicated nail product, ask your pharmacist or healthcare provider whether to pause it before sampling, and mention it when you discuss your result.

When to see a healthcare provider instead of (or as well as) testing

A fungal nail test is useful, but it doesn't replace an in-person assessment. See a healthcare provider promptly if:

• You have diabetes, poor circulation or a weakened immune system (see toenail fungus and diabetes).
• There's pain, redness, warmth, swelling or pus around the nail.
• You see a dark streak or spot under the nail with no clear injury. A fungal test can't rule out melanoma.
• The nail is changing quickly, or several nails change at once along with skin or joint symptoms.

How to collect a good sample

A test can only find what's in the sample, so collection matters. With our kit:

1. Remove any nail polish, then wash and dry your foot.
2. Wipe the nail and the clipper with the included alcohol swab.
3. Clip from the affected part of the nail, including as much discoloured or crumbly nail as you comfortably can, following the kit instructions.
4. Seal the clippings in the sample pouch, fill in the form, and mail everything back in the prepaid return envelope.

A negative result can sometimes happen if the clipping didn't include enough affected nail, so take your time with this step. Don't cut into the skin or cause bleeding. If your nails are too thick to clip safely, or you have diabetes or poor circulation, ask a podiatrist, chiropodist or other healthcare provider for help.

Ready when you are

Our kit ships within 24 hours with free tracked shipping, so it's there when the timing is right. Your sample is analysed with qPCR DNA testing and reviewed by a licensed Canadian podiatrist with over 50 years of experience, and your report arrives 4–14 days after your sample reaches us. See a sample report and understanding your results, including when to retest.

Frequently asked questions

How soon after treatment can I retest for nail fungus?

It depends on the treatment and your nail growth, so ask your healthcare provider. Because PCR detects DNA, which can remain after fungi have died, testing soon after treatment may not reflect whether it worked. Waiting until healthy new nail has grown out is often sensible.

Should I test if only one toenail looks abnormal?

Yes, if the change is persistent or spreading. Fungal infections often start in one nail, usually a big toenail, though an old injury can look similar. A test can help tell them apart.

Can I test a nail with polish on it?

Remove all nail polish first, then wash and dry your foot before collecting the sample. Polish can also hide changes, so look at the bare nail before deciding which part to clip.

Is it worth testing if I've had nail fungus before?

Yes. A past infection raises the chance of another one, but a new change could also be from something else. Testing tells you whether fungus is back before you restart treatment.

What if I'm not sure the nail has changed enough to test?

Take clear photos in good light and compare them in a month. If the change is spreading, thickening or crumbling, testing is reasonable. If you're unsure, a pharmacist or family doctor can take a look.

Sources

• American Academy of Dermatology: Nail fungus, causes
• American Academy of Dermatology: Nail fungus diagnosis and treatment
• NHS: Fungal nail infection
• Canadian Dermatology Association: Subungual melanoma
• Canadian Dermatology Association: Nail fungus and infection