Physical exam alone has been shown to be an unreliable method of diagnosing fungal nails. There are many conditions that can make nails look damaged, so even doctors have a difficult time. In fact, studies have found that only about 50% of cases of abnormal nail appearance were caused by fungus. Therefore, laboratory testing is almost always indicated. Some insurance companies may even ask for a laboratory test confirmation of the diagnosis in order for antifungal medicine to be covered. A nail sample is obtained either by clipping the toenail or by drilling a hole in the nail. That piece of nail is sent to a lab where it can by stained, cultured, or tested by PCR (to identify the genetic material of the organisms) to identify the presence of fungus. Staining and culturing can take up to six weeks to get a result, but PCR to identify the fungal genetic material, if available, can be done in about one day. However, this test is not widely used due to its high cost. If a negative biopsy result is accompanied by high clinical suspicion, such as nails that are ragged, discolored, thickened, and crumbly, it warrants a repeat test due to the prevalence of false-negative results in these tests.

Onychomycosis – commonly known as toenail fungus – is characterized by inflammation, pain, and swelling of the toe, as well as yellowing, thickening, and crumbling of the nail itself.  Toenail fungus can be the result of abnormal pH of the skin, continuous exposure to moisture, wearing synthetic socks, compromised immune system, sweat build-up in shoes, poor foot hygiene, or weak circulation such as that caused by diabetes.
There are several doctors who can provide nail fungus treatment. Your primary care provider, a dermatologist, or a podiatrist can treat nail fungus. Any one of these doctors can provide proper diagnosis and prescribe medications specific to fungal infection. A podiatrist or dermatologist may shave the top layer of the nail off or even remove part of the nail.

Fungal nail infections don’t usually lead to serious long-term problems when properly treated, but they may be more serious in certain individuals. This can include people with diabetes or who have a weakened immune system and have trouble fighting off an infection. Even if there is no pain associated with the infection, it is important that you promptly visit your doctor for assessment if you see any abnormal nail changes.
Athlete's foot is a term given to almost any inflammatory skin disease that affects the sole of the foot and the skin between the toes. It is usually scaly and may be a red, raw-appearing eruption with weeping and oozing with small blisters. It affects the feet of athletes and non-athletes alike. Although it is frequently caused by a fungal infection, other causes may be indistinguishable without proper testing.
Wei, Y.-X., Xu, X.-Y., Xu, & Song, X. (2017). A review of antifungal natural products against the pathogenic fungi causing athletes' foot disease. Current Organic Chemistry, 21, 1–13. Retrieved from https://www.researchgate.net/profile/Xun_Song/publication/319128408_A_Review_of_Antifungal_Natural_Products_Against_the_Pathogenic_Fungi_Causing_Athletes'_Foot_Disease/links/59931c65458515c0ce61efa1/A-Review-of-Antifungal-Natural-Products-Against-the-Pathogenic-Fungi-Causing-Athletes-Foot-Disease.pdf
If you have diabetes, you may have reduced blood circulation and nerve supply in your feet. You're also at greater risk of a bacterial skin infection (cellulitis). So any relatively minor injury to your feet — including a nail fungal infection — can lead to a more serious complication. See your doctor if you have diabetes and think you're developing nail fungus.
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