The first thing you can do is to drink water. If this relieves the symptoms, it is considered to be caused by a lack of water in the body and no tests are needed.
For diabetes, blood glucose levels should be checked, and for hyperthyroidism, total thyroid hormone levels and free thyroxine levels should be checked.
The most important test for chronic kidney disease is kidney function, and a kidney biopsy can be done if the cause is clear.
For suspected uremia, a water-inhibition-augmentin test is indicated, and for suspected dry syndrome, histology and autoantibody tests can be completed.