Most of the candida tests have a percentage of reliability depending on their level of sensitivity. I like PCR testing as it's more sensitive and looks for DNA components. It's high level of sensitivity can work against it occassionally, however. Direct cultures are probably the best indicator as you're growing something that exists within the tissue, fluid, or fecal specimen from the body. Blood tests for IgA, IgG, and Igm are known to produce false positives and false negatives.
The best way is to correlate data - case history; signs and symptoms; testing - blood, saliva, fecal, urine and direct tissue or fluid samples; and effects of treatment protocols. If you do an anti-candida program and get results, that can be a positive indicator that you have/had candida. An MD may not agree, but if they gave a medicine and saw results, then they would think the same way.
I think what you're having problems with is the belief that the medical profession is knowledgable about health. That hasn't been true since around the turn of the 1900s. Consider this, if you thought that an MD didn't know enough about health to be a reliable source for consulting, then you probably wouldn't put much belief or faith in whatever they said, or go to them for advise in the first place. This is where we as a society should be starting from when we view today's medical profession. With this mindset, we can view whatever they say as just an opinion, and decide if it is valid for us or not. From the experience of millions of people on the planet, it hasn't been valid for about 100 years. I view the medical profession as a failed profession on the whole. Their usefulness is now limited to emergency or trauma care. Anything about health is outside their scope of practice.
As a doctor and researcher, I can tell you that we know about 1% of what goes on in the body. Humans are multi-diminsional beings who are affected physically, mentally, emotionally, and spiritually. All of these levels affect one another.
Humans are also super-organisms. We have 10 trillion human cells and 100 trillion micro-organism cells that make-up the body. From this perspective, we are only 10% human. If you consider the number of genes present in the body, then we are 1% human and 99% micro-organism. Care of the micro-organism population is of vital importance and an area that MDs have zero understanding about. Do you really want to turn over your health, your body, and your trust to such an individual? Not me.
When it comes to candida, past antibiotic use is all the positive indicator that I need. Years of study and clinical practice in this field show this to be the true indicator. The rest is a nice attempt to understand a vast field.