It depends on where you have the thrush. Thrush is the term usually referring to a yeast infection. The yeast is almost always Candida species. It is common for people with normal immune systems to get yeast infections in certain places, but most commonly in and around the vagina in females because that is an area which is moist and warm and offers the perfect conditions for yeast to grow. HOWEVER, getting yeast infections in other sites can be an indication something is wrong. Usually if you have yeast infections in the mouth or esophagus, there is some predisposing factor which is usually an impaired immune system. Advanced HIV is an explanation, but so is chemotherapy for cancer, being on steroids like prednisone etc.
So if one is previously healthy and on no medications and shows up with oral thrush or esophageal thrush, one test that MUST be done is an HIV. If another person, however, shows up with a vaginal yeast infection, that is quite common and no further testing is required unless it happens repeatedly.
Getting re-occurring thrush could mean having the milder form of diabetes. (The one that means you have it, but not bad enough to need insulin).
An ex girlfriend of mine kept giving me thrush (mouth and down stairs). I did some intensive googling on the net, before confronting her, because I didn’t know what thrush looked like.
After confronting her, it turned out she had diabetes.