According to what I read from Alletess Lab, less than 100 is normal. So, the test is negative.
There is only one more test I can advice. Candida Delayed Hypersensitivity on Skin. If this test is positive, I doubt he has a persistent yeast overgrowth that doesn’t respond to a systemic drug treatment, at least it be a very resistant yeast species such as candida krusei, glabrata, etc.