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Antidiuretic Hormone (Vasopressin)
(Arginine Vasopressin – Water Balance & Osmoregulation Hormone)
Synonyms
- Antidiuretic Hormone (ADH)
- Vasopressin
- Arginine Vasopressin (AVP)
- Pitressin (older clinical term)
- AVP hormone
- Water-retaining hormone
Units of Measurement
pmol/L, ng/L, ng/dL, ng/100mL, ng%, pg/mL
(Modern labs often use pg/mL or pmol/L via LC-MS/MS.)
Description
Antidiuretic hormone (ADH), also called vasopressin, is a peptide hormone synthesized in the hypothalamus and stored in the posterior pituitary.
ADH regulates:
- Water retention in kidneys
- Plasma osmolality
- Blood pressure (vasoconstriction)
ADH secretion is stimulated by:
- ↑ Plasma osmolality
- ↓ Blood volume or pressure
- Stress, pain, nausea
- Drugs (e.g., carbamazepine)
ADH measurement is essential in evaluating:
- Diabetes insipidus (central vs nephrogenic)
- SIADH (Syndrome of Inappropriate ADH Secretion)
- Hyponatremia workup
- Water-balance disorders
Physiological Role
1. Renal Water Conservation
ADH acts on V2 receptors in renal collecting ducts → inserts aquaporin-2 channels → water reabsorption ↑.
2. Vasoconstriction
At high levels, ADH acts on V1 receptors, causing:
- Arteriolar constriction
- Increased blood pressure
3. Osmoregulation
ADH secretion finely regulated by hypothalamic osmoreceptors.
Clinical Significance
Elevated ADH
1. SIADH (Most Common Cause)
Results in:
- Hyponatremia
- Low serum osmolality
- High urine osmolality
- Excess free-water retention
Causes:
- CNS disorders (stroke, infection, trauma)
- Lung diseases (pneumonia, small-cell carcinoma)
- Drugs (SSRIs, carbamazepine, cyclophosphamide)
2. Volume Depletion / Hypotension
- Heart failure
- Cirrhosis
- Kidney failure
- Severe dehydration
- Shock
3. Stress-Related Increases
- Pain, surgery, nausea
- Exercise
- Hypoglycemia
Low ADH
1. Central Diabetes Insipidus (CDI)
- Deficient ADH secretion
- Causes: trauma, pituitary surgery, tumors, autoimmune, idiopathic
- Leads to: polyuria, polydipsia, hypernatremia
2. Nephrogenic Diabetes Insipidus (NDI)
- Kidney unresponsive to ADH → ADH levels normal or high
(BUT measured ADH may appear low in partial NDI.)
3. Primary Polydipsia
- Excessive water intake suppresses ADH
- Euvolemic hypo-osmolality
Reference Intervals
(Tietz 8E + Mayo + ARUP + Endocrine Society)
Basal ADH (Non-stressed, normal hydration)
- 1.0 – 5.0 pg/mL
- ≈ 0.5 – 2.5 pmol/L
At Plasma Osmolality of 280–295 mOsm/kg
ADH should rise linearly:
- 1 pg/mL increase per 1 mOsm/kg increase (approx.)
SIADH
- Inappropriately high ADH despite low plasma osmolality
Diabetes Insipidus
- Low ADH (<1 pg/mL), especially when osmolality is high
Plasma Copeptin (Modern Alternative)
Copeptin is the C-terminal part of the ADH precursor; more stable.
Used for:
- Diagnosing DI vs primary polydipsia
- Hypertonic saline / water-deprivation tests
Unit Meanings
| Unit | Meaning |
| pmol/L | picomole per liter |
| pg/mL | picogram per milliliter |
| ng/L | nanogram per liter (same as pg/mL × 1000 ÷ 1,000,000) |
| ng/dL | nanogram per deciliter |
| ng/100 mL | same as ng% |
| ng% | nanogram per 100 mL |
Diagnostic Uses
1. Differentiating DI vs SIADH
| Disorder | ADH Level | Clinical Picture |
| Central DI | Low | Polyuria + hypernatremia |
| Nephrogenic DI | Normal/High | Kidney resistant |
| Primary Polydipsia | Low | Diluted plasma + low urine osmolality |
| SIADH | High | Hyponatremia + concentrated urine |
2. Hyponatremia Evaluation
ADH helps determine etiology in complex cases.
3. Postoperative/Trauma Monitoring
ADH spikes may contribute to water retention.
Analytical Notes
- ADH is unstable - requires frozen plasma (EDTA)
- Rapid processing essential
- Copeptin preferred in many centers due to better stability
- Hemolysis minimal effect
- Elevated bilirubin/lipemia may interfere depending on assay
Clinical Pearls
- ADH levels must always be interpreted with serum and urine osmolality.
- Copeptin is now preferred for water-deprivation testing.
- Stress, pain, nausea, and smoking increase ADH even in healthy people.
- SIADH diagnosis is clinical; ADH helps in tricky cases.
- Lithium therapy → common cause of nephrogenic DI.
Interesting Fact
ADH (vasopressin) was discovered in the early 20th century and was one of the first hormones isolated from the posterior pituitary - earning recognition for its dual role in blood pressure regulation and water balance.
References
- Tietz Clinical Chemistry and Molecular Diagnostics, 8th Edition - Peptide Hormones.
- Endocrine Society Clinical Guidelines - Water Balance, DI & SIADH.
- Mayo Clinic Laboratories - ADH & Copeptin Testing.
- ARUP Consult - Hyponatremia & DI Workup.
- IFCC Hormone Standardization.
- MedlinePlus / NIH - Vasopressin Overview.
- UpToDate - Evaluation of Polyuria & Hyponatremia.