Is an Antidiuretic Hormone (ADH) level of less than 0.8 indicative of diabetes insipidus?

Is an ADH Level <0.8 Indicative of Diabetes Insipidus?

No, measuring ADH levels is not recommended for diagnosing diabetes insipidus, as ADH measurement has limited diagnostic value and lacks a defined threshold for "appropriateness," including the 0.8 cutoff you mention. 1

Why ADH Measurement Is Not Useful

The 2009 Neurosurgery guidelines explicitly state that obtaining levels of hormones such as ADH is not supported by the literature (class III evidence) 1. The fundamental problem is that the "appropriateness" of any ADH level—including values below 0.8—has never been properly defined in the medical literature 1.

Key Problems with ADH Testing

• SIADH has been documented in patients with no detectable ADH, demonstrating that ADH levels don't correlate reliably with clinical syndromes 1
• ADH can be detectable in all patients regardless of whether they develop hyponatremia early or late after injury 1
• The available data on ADH levels are conflicting and unreliable for clinical decision-making 1

What You Should Use Instead

Plasma copeptin is the preferred diagnostic test, serving as a superior surrogate marker for ADH 2, 3:

• Copeptin >21.4 pmol/L indicates nephrogenic DI 2, 3
• Copeptin <21.4 pmol/L suggests central DI or primary polydipsia 2, 3

Proper Diagnostic Approach to Diabetes Insipidus

The diagnosis relies on clinical and laboratory findings, not ADH levels 2, 3:

Pathognomonic Features

• Urine osmolality <200 mOsm/kg combined with high-normal or elevated serum sodium is diagnostic for diabetes insipidus 3
• Hypotonic polyuria with large volumes of dilute urine 2
• Polydipsia with extreme thirst and craving for water 2

Diagnostic Algorithm

1. Confirm inappropriately dilute urine (osmolality <200 mOsm/kg) in the setting of elevated serum osmolality 2, 3
2. Measure plasma copeptin to distinguish central from nephrogenic DI 2, 3
3. Consider desmopressin trial: response confirms central DI, while lack of response indicates nephrogenic DI 3
4. Exclude primary polydipsia, which shows urine concentration with water deprivation and typically presents with lower serum sodium 3

Critical Management Considerations

Before initiating treatment, serum sodium must be confirmed as normal and the specific type of DI must be established 3:

• For central DI: Desmopressin is the treatment of choice 2, 3
• For nephrogenic DI: Thiazide diuretics combined with dietary salt restriction and prostaglandin synthesis inhibitors 2, 3

Common Pitfall to Avoid

Do not order ADH levels when evaluating for diabetes insipidus—this test will not help you make the diagnosis and may lead to confusion given the lack of established diagnostic thresholds 1. Instead, rely on the combination of clinical presentation, urine osmolality, serum sodium, and copeptin measurement 2, 3.