Which test is described as the SIADH diagnostic test in the material?

• A. No fluid for 8 hours
• B. Overnight Water Deprivation Test
• C. Water Loading Test
• D. Serum Sodium Challenge

Answer: (A)

In SIADH, the body retains too much free water because ADH is inappropriately active, which dilutes the serum sodium. A practical way to probe this tendency is to restrict water intake and see how the sodium balance responds. Withholding fluids for about eight hours directly challenges the system to handle water without an ongoing intake. In the material’s scheme, this brief fluid-restriction test is described as the SIADH diagnostic test because a patient with SIADH shows a characteristic response (the hyponatremia reflects water retention and is revealed under restricted intake, helping distinguish this pattern from other causes of hyponatremia). The other tests listed are not used in that material to diagnose SIADH: the overnight water deprivation test is more characteristic of assessing conditions like diabetes insipidus, the water loading test assesses the body's ability to excrete a large water load, and the serum sodium challenge is not a standard SIADH diagnostic approach.