ADH Levels in Diabetes Insipidus
Measuring ADH levels has limited diagnostic value in diabetes insipidus and is not recommended for routine clinical use. 1
Why ADH Testing Is Not Recommended
The "appropriateness" of an ADH level has never been clearly defined in the medical literature, making interpretation problematic. 1 More importantly, SIADH has been documented in patients with no detectable ADH, demonstrating that ADH levels do not reliably correlate with clinical syndromes of water balance disorders. 1
Key Evidence Against Routine ADH Measurement
Neurosurgery guidelines explicitly state that obtaining levels of hormones such as ADH and natriuretic peptides is not supported by the literature (class III evidence). 1
In prospective studies of severe head injury patients, ADH was detectable in all patients regardless of whether they developed hyponatremia, further demonstrating poor discriminatory value. 1
The available data on ADH levels in various conditions are conflicting and inconsistent, making clinical interpretation unreliable. 1
What to Measure Instead
Use plasma copeptin levels as the primary differentiating test to distinguish between central and nephrogenic diabetes insipidus. 2, 3
Copeptin-Based Diagnostic Algorithm
Copeptin >21.4 pmol/L indicates nephrogenic diabetes insipidus (kidney resistance to ADH). 2, 3
Copeptin <21.4 pmol/L suggests central diabetes insipidus or primary polydipsia, requiring additional testing with hypertonic saline or arginine stimulation. 2
Copeptin is a stable surrogate marker of ADH that provides superior diagnostic accuracy compared to direct ADH measurement. 4
Recommended Diagnostic Approach
The initial biochemical work-up should include simultaneous measurement of serum sodium, serum osmolality, and urine osmolality—not ADH levels. 2, 3
Diagnostic Criteria for Diabetes Insipidus
Urine osmolality <200 mOsm/kg H₂O combined with high-normal or elevated serum sodium is pathognomonic for diabetes insipidus. 2
This triad of polyuria, polydipsia, and inappropriately dilute urine confirms the diagnosis without needing ADH measurement. 2
A water deprivation test followed by desmopressin administration remains the gold standard when the diagnosis is uncertain. 4, 5
Clinical Pitfall to Avoid
Do not order ADH levels thinking they will help differentiate between central and nephrogenic diabetes insipidus—they will not provide clinically useful information and may lead to diagnostic confusion. 1 Instead, use the copeptin-based approach or perform a desmopressin trial, where response to desmopressin indicates central diabetes insipidus and no response indicates nephrogenic diabetes insipidus. 2