• Ivan Bristow

A new five minute test for tinea unguium


Tinea unguium is a very common nail infection we see in clinic. By definition, it is invasion of the nail plate by dermatophytes. In my article “Be sure of the cure” in Podiatry Now I discussed the importance of a proper diagnosis of fungal nail infection which is echoed in the published guidelines for onychomycosis (1). For many years, I think as podiatrists we have become hesitant to test for many reasons. Probably the most common is when you do, so often the results come back negative despite clinical evidence to contrary. This is a well reported factor with microscopy and culture – a high false negative rate of 30% (2). This comes about for many reasons - insufficient sample/lack of sample quality or the skill of the operator examining with microscopy. The other of course is the cost which can be high and must be borne by the patient in private practice. Or, you end up writing a letter to the GP requesting that they send it on using NHS services. The results too, can take up to three weeks to be available. This is a long time to wait - particularly if the results are negative.

Working with a lot of patients with fungal nail disease, I was well aware of these issues and often frustrated by the high negative result rates. In 2014, I read a paper in the British Journal of Dermatology which investigated a new rapid test for fungal nail disease (3). The product wasn’t available at that time, but I managed to acquire a sample of the product to test in the clinic. The Dermatophyte Test Strip (DTS) reportedly could can return an accurate diagnosis in under 5 minutes, while the patient is still in the chair. After trying it using obviously infected and uninfected nails, I moved onto nails I wasn’t sure about and felt the test was giving consistent results.

The test works using the same technology as a pregnancy kit – an immunoassay test. Simply, a sample of nail is added to a disposable test tube, a solution is added, and the sample is stirred so it softens the nail sample. The test strip is then placed into the mixture and drawn up the test strip just like litmus paper.

Here’s the clever bit – inside the DTS is a gold colloid impregnated with antibodies specifically primed to detect dermatophyte protein. If any is found in the sample the strip signifies this with a purple-brown line appearing below a pink test line (which confirms the test has worked). So why did this get me excited? Well, firstly, the research from the British Journal of Dermatology and Japanese Journal of Dermatology (4) assessed its accuracy by comparing to microscopy and culture. This is interesting to begin with because these techniques are known to be less than accurate. Consequently, the DTS showed more positives than these in the work. So, to fully assess if it was correct, it was compared against the laboratory gold standard test – Polymerase Chain Reaction (PCR). PCR works by detecting Fungal DNA in a sample and amplifying it. As it is a computerised operation, needless to say it is highly accurate in determining the presence or absence of dermatophytes. The comparison consequently showed that the DTS was over 97% accurate when compared to PCR, meaning it was a simple clinical test with laboratory power behind it.

The advantages?

  1. The test is simple to use.

  2. It only takes 5 minutes to work.

  3. It only needs 0.1 gram of dermatophyte material in a sample to elicit a positive result.

  4. The test kit can detect 8 species of dermatophytes. These collectively in UK (according to mycology lab reference data) are responsible for over 99% of dermatophyte skin infections (5).

  5. T rubrum, T mentagrophytes (var. interdigitale) and E floccosum are all detected by the test. These three alone make up 90% of dermatophyte infections in the UK (5).

  6. Unlike culture, the test is unaffected if the patient has been using antifungals.

Probably, the most surprising thing was that patients enjoyed taking part in the test by holding the strip and observing for any colour change which helped them to understand the diagnosis and its importance. The test strip retails at £20 (per test) in the UK and so it below the cost of any laboratory tests and this was easily incorporated into our fees to ensure it was good business. As we had an immediate diagnosis we could inform the patient (and their GP) straight away and advise on suitable treatment directions whether that was do nothing, Clearanail® or topical antifungals, for example.

As it turned out, they had no distributors at that time, but as the saying goes, we were so impressed we took on the UK and Irish distribution rights ourselves as we thought it was a great opportunity for Podiatrists to grow their business with probably the commonest infection seen in clinic.

Full details of the test along with videos can be found on the website: www.fiveminutefungus.com

Declaration: The author is director of the company which distributes retails this product in the UK and Ireland.

References

1. Roberts DT, Taylor WD, Boyle J. Guidelines for treatment of onychomycosis. Br J Dermatol. 2003;148(3):402-10.

2. Fletcher CL, Hay RJ, Smeeton NC. Onychomycosis:the development of a clinical diagnostic aid for toenail disease. Part 1.Establishing discrimanting historical and clinical features. Brit J Dermatol. 2004;150:701-5.

3. Tsunemi Y, Takehara K, Miura Y, Nakagami G, Sanada H, Kawashima M. Screening for tinea unguium by Dermatophyte Test Strip. Br J Dermatol. 2014;170(2):328-31.

4. Tsunemi Y, Hiruma M. Clinical study of Dermatophyte Test Strip, an immunochromatographic method, to detect tinea unguium dermatophytes. The Journal of Dermatology. 2016;43(12):1417-23.

5. Borman AM, Campbell CK, Fraser M, Johnson EM. Analysis of the dermatophyte species isolated in the British Isles between 1980 and 2005 and review of worldwide dermatophyte trends over the last three decades. Med Mycol. 2007;45(2):131 - 41.

#onychomycosis #fungal #nail #diagnosis

0 views