To investigate the cause of polyuria polydipsia syndrome, i.e. excessive urination and excessive drinking. Rarely this may be due to deficiency of, or lack of response to, ADH.
Diagnosis of conditions of ADH excess is usually based on clinical history and other laboratory tests, such as blood and urine osmolality as well as electrolytes.
ADH or copeptin may be requested if the results of initial investigation of polyuria polydipsia syndrome are inconclusive. ADH and copeptin are usually only measured as part of stimulation testing; either the water deprivation test or the saline infusion test. ADH or copeptin analysis on a random, or unstimulated, sample is rarely required.
A blood sample is obtained by inserting a needle into a vein in the arm.
Alcohol and some medications (including diuretics) can interfere with ADH and copeptin secretion, or ADH action. Talk to your doctor to identify any medications that should be discontinued before the test.
The water deprivation test and saline infusion test have specific preparation requirements. Talk to your doctor to determine what preparation is required for these tests.
Measurement of ADH or copeptin is not widely required. The investigation of polyuria polydipsia syndrome may include measurement of ADH or copeptin, usually as part of a water deprivation test or saline infusion test. Only in exceptional circumstances ADH or copeptin measurement may be required to help investigate hyponatraemia and its associated symptoms, and to identify SIADH.
Symptoms of ADH deficiency are often seen with one of two types of diabetes insipidus. Central diabetes insipidus is a decrease in the production of ADH by the hypothalamus or in the release of ADH from the pituitary; nephrogenic diabetes insipidus is characterised by a decrease in the kidney's response to ADH. A water deprivation test or saline infusion test is the preferred means to diagnose diabetes insipidus and distinguish between the central and nephrogenic forms. The water deprivation test involves collection of several timed urine and blood samples for osmolality analysis during strictly controlled fluid restriction and after administration of synthetic ADH (ddAVP). The saline infusion test involves infusion of a small volume of fluid into a vein over a short time period, with collection of several timed blood samples for electrolyte, osmolality and ADH or copeptin analysis. Both procedures must be performed under close medical supervision as it can sometimes lead to severe dehydration and can pose a risk to some people with underlying diseases. The levels of ADH or copeptin obtained are used to determine if there is an appropriate ADH response to a hyperosmolar stimulus.
Symptoms of increased levels of ADH are often seen with "Syndromes of Inappropriate ADH production" or SIADH. Testing for SIADH may include blood and urine osmolality, blood and urine sodium, and tests to exclude poor renal or adrenal function. Measurement of ADH or copeptin for the diagnosis of SIADH is only required in exceptional circumstances.
Measurement of ADH or copeptin is not widely required. The investigation of polyuria polydipsia syndrome may include measurement of ADH or copeptin, usually as part of a water deprivation test or saline infusion test. Only in exceptional circumstances ADH or copeptin measurement may be required to help investigate hyponatraemia and its associated symptoms, and to identify SIADH.
ADH or copeptin test results alone are not diagnostic of a specific condition. The results are usually evaluated in conjunction with a person's medical history, physical examination, and results of other tests. Excesses and deficiencies of ADH may be temporary or persistent, acute or chronic, and may be due to an underlying disease, an infection, an inherited condition, due to a surgery or trauma, or even due to a psychological problem that leads to excess water drinking.
Increased ADH or copeptin concentrations are often associated with SIADH and may be seen with a variety of cancers, including leukaemia, lymphoma, lung cancer, pancreatic, bladder, and brain cancer. Greatly increased concentrations of ADH or copeptin may be seen with systemic cancers that produce ADH. Moderate increases may be seen with nervous system disorders such as Guillain-Barré syndrome, multiple sclerosis, epilepsy, acute intermittent porphyria, with pulmonary disorders such as cystic fibrosis, emphysema, and tuberculosis, and in those with HIV/AIDS. Measurement of ADH or copeptin for the diagnosis of SIADH is only required in exceptional circumstances.
A low ADH or copeptin result may be seen with central diabetes insipidus, primary polydipsia, and with low serum osmolality. An increased ADH or copeptin concentration may be seen in nephrogenic diabetes insipidus, with dehydration, trauma, and surgery.
With the water deprivation test or saline infusion test, a doctor is looking at the response (in either urine osmolality or blood ADH/copeptin) to a hyperosmolar stimulus. In central diabetes insipidus, the ADH or copeptin is low and does not rise appropriately. In nephrogenic diabetes insipidus the ADH or copeptin is high from the outset. In primary polydipsia the ADH or copeptin is low, but does increase in response to hyperosmolar stimulation.
In general, the ability to concentrate urine decreases with age.
ADH secretion increases when a person is standing, at night, and with pain, stress and exercise. Secretion decreases with hypertension and when someone is lying down.
Many drugs can affect ADH levels. They include:
Samples for ADH need to reach the laboratory very quickly. ADH is unstable in the withdrawn blood: the serum must be separated from the blood cells and frozen as soon as possible, therefore the test is not suitable to be ordered from a GP practice. Copeptin is very stable in withdrawn blood and could in theory be ordered from a GP practice. However it is unusual to order copeptin outside of simulation testing (water deprivation test or saline infusion test), which would always be performed in a hospital setting under medical supervision. Only a few laboratories offer ADH or copeptin analysis and so the sample may need to be sent to a reference laboratory.
Diabetes mellitus, usually referred to as diabetes, is related to either decreased insulin production or insulin resistance and causes an increase in blood glucose. Diabetes insipidus is not related to insulin or glucose, but both diabetes conditions can cause increased thirst and frequent urination.
Yes, a synthetic form of ADH can be given as a replacement to those with central diabetes insipidus. Those with nephrogenic diabetes insipidus are encouraged to drink adequate amounts of water to replace what is being lost in their urine and should talk to their doctor about possible adjustments to their diet.