ADH (Antidiuretic Hormone) Test: Purpose, Normal Range & High/Low Causes

What is ADH (Antidiuretic Hormone)?

ADH, or Antidiuretic Hormone, also known as vasopressin, is a hormone responsible for regulating the body’s water balance.
It helps control how much water the kidneys reabsorb and how much is excreted as urine, ensuring the body maintains proper hydration and blood pressure.

The ADH test measures the amount of this hormone in the blood to help diagnose conditions related to fluid balance, dehydration, excess urination, or low sodium levels.

Where is ADH Produced in the Body?

ADH is produced by the hypothalamus, a region in the brain that controls many vital functions.
Specifically:

• It is synthesized in the supraoptic and paraventricular nuclei of the hypothalamus.
• Then, it is stored and released by the posterior pituitary gland (neurohypophysis) when the body needs to conserve water.

This system allows precise control of the body’s hydration and electrolyte balance.

Main Functions and Importance of ADH

The antidiuretic hormone plays multiple essential roles in maintaining body homeostasis:

1. Regulates Water Balance

ADH increases water reabsorption in the kidneys’ collecting ducts, reducing urine output and preventing dehydration.

2. Maintains Blood Pressure

By constricting blood vessels (vasoconstriction), ADH helps raise or stabilize blood pressure, especially during dehydration or blood loss.

3. Controls Urine Concentration

When ADH levels are high, urine becomes concentrated and darker.
When ADH is low, urine becomes diluted and pale, leading to excessive urination.

4. Balances Electrolytes

ADH indirectly helps regulate sodium (Na⁺) and potassium (K⁺) levels, ensuring the proper balance of fluids inside and outside cells.

Causes of Low ADH Levels

Low levels of ADH result in excessive water loss through urine, a condition known as Diabetes Insipidus (DI).

Common causes include:

• Central Diabetes Insipidus: The hypothalamus or pituitary fails to produce enough ADH.
• Nephrogenic Diabetes Insipidus: The kidneys do not respond properly to ADH.
• Head injury or brain surgery: Damage to the hypothalamus or pituitary gland.
• Genetic disorders: Rare inherited ADH deficiencies.
• Excessive water intake (psychogenic polydipsia): Drinking too much water can suppress ADH.

Symptoms of Low ADH Levels

• Excessive urination (polyuria) – large amounts of very dilute urine
• Extreme thirst (polydipsia)
• Dehydration (dry mouth, dry skin, sunken eyes)
• High sodium levels (hypernatremia)
• Fatigue or weakness due to dehydration

Causes of High ADH Levels

High levels of ADH lead to water retention, reduced urine output, and low sodium concentration in the blood.

Common causes include:

• SIADH (Syndrome of Inappropriate Antidiuretic Hormone Secretion): Excessive ADH production, causing water retention and low sodium.
• Stress, pain, or surgery: Temporary increase in ADH release.
• Certain cancers: Especially small-cell lung cancer, which can produce ADH abnormally.
• Medications: SSRIs, carbamazepine, cyclophosphamide, and some anticonvulsants.
• Severe infections or trauma

Symptoms of High ADH Levels

Symptoms are mainly due to water overload and low sodium (hyponatremia):

• Low urine output (oliguria)
• Water retention and swelling (edema)
• Headache, confusion, or dizziness
• Nausea and vomiting
• Seizures or coma (in severe cases due to hyponatremia)

Reference Ranges

Normal plasma ADH levels vary depending on hydration and the laboratory method used.

🔹 Levels may vary by lab and must be interpreted along with blood sodium and urine osmolality tests.

Sample Type and Handling

How the ADH Test is Performed

1. A blood sample is drawn from a vein, usually in the morning.
2. The sample is collected in a cold EDTA tube, kept on ice, and sent immediately to the lab.
3. ADH levels are measured using a radioimmunoassay or chemiluminescent assay.
4. Often, plasma osmolality and urine osmolality are also tested to help interpret the ADH level.

Interpreting ADH Test Results

⚠️ ADH results should always be interpreted along with sodium, osmolality, and clinical symptoms.

Test Preparation

• Avoid excessive fluid intake 24 hours before testing unless advised otherwise.
• Inform your doctor about any medications you’re taking — antidepressants, anticonvulsants, or diuretics can affect ADH levels.
• The test is best performed in the morning when natural hormone variations are minimal.
• Samples must be handled rapidly and kept chilled to ensure accurate results.

When to Consult a Doctor

Consult a healthcare provider if you experience:

• Excessive thirst or urination
• Unexplained swelling or low urine output
• Sudden confusion, headache, or drowsiness
• Dehydration symptoms despite drinking water
• Changes in sodium or electrolyte levels

These may indicate hormonal imbalance, dehydration, or a kidney disorder requiring an ADH test.

Important Word Explanations

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