Antidiuretic Hormone (ADH / Vasopressin) Test
Overview
The Antidiuretic Hormone (ADH) test, also known as the Vasopressin test, measures the amount of ADH in the plasma (the liquid part of the blood). ADH is a hormone produced by the hypothalamus and stored and released by the posterior pituitary gland. Its main role is to regulate the body’s water balance by controlling how much water the kidneys reabsorb.

When the body is dehydrated or has low blood volume, ADH is released to conserve water. Abnormal ADH levels can indicate problems with fluid regulation, kidney function, or pituitary gland disorders.

Sample Type
Plasma (from a blood sample, often collected with special handling and sometimes accompanied by urine and electrolyte measurements)

Purpose of the Test
This test is used to help diagnose or evaluate:

Diabetes Insipidus (central or nephrogenic)

Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)

Hyponatremia (low sodium levels)

Hypovolemia or Hypervolemia (abnormal blood volume)

Water balance disorders linked to hypothalamic or pituitary dysfunction

Understanding the Results
ADH Level Possible Indication
High SIADH, dehydration, stress, heart failure, hypothyroidism
Low Central diabetes insipidus, excessive fluid intake (psychogenic polydipsia), certain kidney conditions

🔍 Note: ADH levels are best interpreted alongside plasma osmolality and urine osmolality to determine the underlying cause of fluid imbalance.

When Is It Ordered?
Your healthcare provider may order an ADH test if you have:

Excessive thirst and urination

Very dilute or very concentrated urine

Unexplained low sodium levels

Symptoms of pituitary or hypothalamic dysfunction

Post-surgical monitoring after pituitary surgery

Preparation & Procedure
Preparation: May require fasting and limited fluid intake before the test

Procedure: Blood is drawn (usually under controlled conditions) and plasma is separated and tested in a specialized laboratory

Often combined with:

Serum electrolytes (especially sodium)

Plasma and urine osmolality

Urine volume measurement

Related Conditions
Central Diabetes Insipidus – low ADH production from the brain

Nephrogenic Diabetes Insipidus – kidneys do not respond to ADH

SIADH – excessive ADH leading to water retention and low sodium

Hyponatremia – low sodium due to fluid imbalance

Conclusion
The ADH (Vasopressin) test plays a key role in diagnosing disorders related to fluid and electrolyte balance. Abnormal levels can indicate conditions like diabetes insipidus, SIADH, or other hormonal and kidney-related disorders. Because ADH works in close coordination with sodium and water regulation, it is essential to interpret test results alongside other related measurements.