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Introduction ⬇

Antidiuretic hormone (ADH) is secreted by the posterior pituitary gland. Its major physiologic function is regulation of body water. In the dehydrated (hyperosmolar) state, ADH release results in decreased urine excretion and conservation of water. ADH increases blood pressure.

When ADH activity is present, small volumes of concentrated urine are excreted. When ADH is absent, large amounts of diluted urine are produced. Higher secretion occurs at night, with erect posture, and with pain, stress, or exercise. Measurement of the level of ADH is useful in the differential diagnosis of polyuric and hyponatremic states. ADH testing aids in diagnosis of urine concentration disorders, especially diabetes insipidus, SIADH, psychogenic water intoxication, and syndromes of ectopic ADH production.

Normal Findings ⬆ ⬇

<2.5 pg/mL or <2.3 pmol/L

Procedure ⬆ ⬇

  1. Draw venous blood samples, 5 mL, into prechilled tubes and put on ice. Plasma with EDTA anticoagulant is needed. Observe standard precautions. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

  2. Ensure that the patient is in a sitting position and calm during blood collection.

Clinical Implications ⬆ ⬇

  1. Increased secretion of ADH is associated with the following conditions:

    1. SIADH (with respect to plasma osmolality)

    2. Ectopic ADH production (systemic neoplasm)

    3. Nephrogenic diabetes insipidus

    4. Acute intermittent porphyria

    5. Guillain-Barré syndrome (acute polyneuropathy, ascending paralysis)

    6. Brain tumor, diseases, injury, neurosurgery

    7. Pulmonary diseases (tuberculosis)

  2. Decreased secretion of ADH occurs in the following conditions:

    1. Central diabetes insipidus (hypothalamic or neurogenic)

    2. Psychogenic polydipsia (water intoxication)

    3. Nephrotic syndrome

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure.

  2. Encourage relaxation before and during blood-drawing procedure.

  3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Have the patient resume normal activities.

  2. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel appropriately for urine concentration disorders and polyuria.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Clinical Alert

To distinguish SIADH from other conditions that cause dilutional hyponatremia, other tests must be done, such as plasma osmolality, plasma sodium, and water-loading tests

Interfering Factors ⬆

  1. Recently administered radioisotopes cause spurious results.

  2. Many drugs affect results (e.g., thiazide diuretic agents, oral hypoglycemic agents, narcotic drugs); see Appendix E.