Deficiencies in both total body water and total body sodium exist, although proportionally more sodium than water has been lost; the sodium deficit causes hypovolemia. In hypovolemic hyponatremia, both serum osmolality and blood volume decrease. Vasopressin (antidiuretic hormone [ADH]) secretion increases despite a decrease in osmolality to maintain blood volume. The resulting water retention increases plasma dilution and hyponatremia.
Extrarenal fluid losses, such as those that occur with the losses of sodium-containing fluids as in protracted vomiting, severe diarrhea, or sequestration of fluids in a 3rd space (see table Composition of Body Fluids Composition of Body Fluids
Renal fluid losses resulting in hypovolemic hyponatremia may occur with mineralocorticoid deficiency Addison Disease Addison disease is an insidious, usually progressive hypofunctioning of the adrenal cortex. It causes various symptoms, including hypotension and hyperpigmentation, and can lead to adrenal crisis... read more , thiazide diuretic therapy, osmotic diuresis, or salt-losing nephropathy. Salt-losing nephropathy encompasses a loosely defined group of intrinsic renal disorders with primarily renal tubular dysfunction. This group includes interstitial nephritis Tubulointerstitial Nephritis Tubulointerstitial nephritis is primary injury to renal tubules and interstitium resulting in decreased renal function. The acute form is most often due to allergic drug reactions or to infections... read more , medullary cystic disease Nephronophthisis and Autosomal Dominant Tubulointerstitial Kidney Disease (ADTKD) Nephronophthisis and autosomal dominant tubulointerstitial kidney disease (ADTKD) are inherited disorders that cause cysts restricted to the renal medulla or corticomedullary border and, eventually... read more , partial urinary tract obstruction, and, occasionally, polycystic kidney disease Autosomal Dominant Polycystic Kidney Disease (ADPKD) Polycystic kidney disease (PKD) is a hereditary disorder of renal cyst formation causing gradual enlargement of both kidneys, sometimes with progression to renal failure. Almost all forms are... read more .
Diuretics may also cause hypovolemic hyponatremia. Thiazide diuretics, in particular, decrease the kidneys’ diluting capacity and increase sodium excretion. Once volume depletion occurs, the nonosmotic release of vasopressin causes water retention and worsens hyponatremia. Concomitant hypokalemia shifts sodium intracellularly and enhances vasopressin release, thereby worsening hyponatremia. This effect of thiazides may last for up to 2 weeks after cessation of therapy; however, hyponatremia usually responds to replacement of potassium and volume deficits along with judicious monitoring of water intake until the drug effect dissipates. Older patients may have increased sodium diuresis and are especially susceptible to thiazide-induced hyponatremia, particularly when they have a preexisting defect in renal capacity to excrete free water. Rarely, such patients develop severe, life-threatening hyponatremia within a few weeks after the initiation of a thiazide diuretic. Loop diuretics much less commonly cause hyponatremia.
What is an antidiuretic hormone (ADH) test?
Antidiuretic hormone (ADH) is a hormone that helps your kidneys manage the amount of water in your body. The ADH test measures how much ADH is in your blood. This test is often combined with other tests to find out what is causing too much or too little of this hormone to be present in the blood.
ADH is also called arginine vasopressin. It’s a hormone made by the hypothalamus in the brain and stored in the posterior pituitary gland. It tells your kidneys how much water to conserve.
ADH constantly regulates and balances the amount of water in your blood. Higher water concentration increases the volume and pressure of your blood. Osmotic sensors and baroreceptors work with ADH to maintain water metabolism.
Osmotic sensors in the hypothalamus react to the concentration of particles in your blood. These particles include molecules of sodium, potassium, chloride, and carbon dioxide. When particle concentration isn’t balanced, or blood pressure is too low, these sensors and baroreceptors tell your kidneys to store or release water to maintain a healthy range of these substances. They also regulate your body’s sense of thirst.
The normal range for ADH is 1-5 picograms per milliliter (pg/mL). Normal ranges can vary slightly among different laboratories. ADH levels that are too low or too high can be caused by a number of different problems.
ADH deficiency
Too little ADH in your blood may be caused by compulsive water drinking or low blood serum osmolality, which is the concentration of particles in your blood.
A rare water metabolism disorder called central diabetes insipidus is sometimes the cause of ADH deficiency. Central diabetes insipidus is marked by a decrease in either the production of ADH by your hypothalamus or the release of ADH from your pituitary gland.
Common symptoms include excessive urination, which is called polyuria, followed by extreme thirst, which is called polydipsia.
People with central diabetes insipidus are often extremely tired because their sleep is frequently interrupted by the need to urinate. Their urine is clear, odorless, and has an abnormally low concentration of particles.
Central diabetes insipidus can lead to severe dehydration if it’s left untreated. Your body won’t have enough water to function.
This disorder is not related to the more common diabetes, which affects the level of the hormone insulin in your blood.
Excess ADH
When there’s too much ADH in your blood, syndrome of inappropriate ADH (SIADH) may be the cause. If the condition is acute, you may have a headache, nausea, or vomiting. In severe cases, coma and convulsions can occur.
Increased ADH is associated with:
Dehydration, brain trauma, and surgery can also cause excess ADH.
Nephrogenic diabetes insipidus is another very rare disorder that may affect ADH levels. If you have this condition, there’s enough ADH in your blood, but your kidney can’t respond to it, resulting in very dilute urine. The signs and symptoms are similar to central diabetes insipidus. They include excessive urination, which is called polyuria, followed by extreme thirst, which is called polydipsia. Testing for this disorder will likely reveal normal or high ADH levels, which will help distinguish it from central diabetes insipidus.
Nephrogenic diabetes insipidus is not related to the more common diabetes mellitus, which affects the level of insulin hormone in the blood.
A healthcare provider will draw blood from your vein, usually on the underside of the elbow. During this process, the following occurs:
- The site is first cleaned with an antiseptic to kill germs.
- An elastic band is wrapped around your arm above the potential area of the vein where the blood will be drawn. This causes the vein to swell with blood.
- Your healthcare provider gently inserts a needle syringe into your vein. Blood collects in the syringe tube. When the tube is full, the needle is then removed.
- The elastic band is then released, and the needle puncture site is covered with sterile gauze to stop the bleeding.
Many medications and other substances can affect the levels of ADH in your blood. Before the test, your doctor may ask you to avoid:
- alcohol
- clonidine, which is a blood pressure medication
- diuretics
- haloperidol, which is a medication used to treat psychotic and behavioral disorders
- insulin
- lithium
- morphine
- nicotine
- steroids
The uncommon risks of blood tests are:
Abnormally high levels of ADH may mean you have:
Abnormally low levels of ADH may mean:
- pituitary damage
- primary polydipsia
- central diabetes insipidus, which is rare
An ADH test alone is usually not enough to make a diagnosis. Your doctor will probably need to perform a combination of tests. Some tests that may be performed with an ADH test include the following:
- Anosmolality test is a blood or urine test that measures the concentration of dissolved particles in your blood serum and urine.
- An electrolyte screening is a blood test that’s used to measure the amount of electrolytes, usually sodium or potassium, in your body.
- A water deprivation testexamines how frequently you urinate if you stop drinking water for several hours.