|Clinical Use:||Diagnosis and characterization of diabetes insipidus. Diagnosis of psychogenic water intoxication. As an adjunct in the diagnosis of syndrome of inappropriate secretion of antidiuretic hormone secretion (SIADH), including ectopic AVP production|
|Background:||Copeptin is the C terminal peptide of proAVP and is co-secreted on an equimolar basis with AVP from the posterior pituitary. Arginine vasopressin (AVP), also known as antidiuretic hormone (ADH), is a hypothalamic polypeptide that is transported along the axons of the synthesizing neurons into the posterior pituitary gland. From there it is released into the systemic circulation after appropriate stimuli. The main regulators of AVP secretion are osmotic stimuli, provided by osmoreceptors located in the anteromedial hypothalamus, and volume stimuli, provided by receptors in neck vessels and heart.
Under physiological conditions, volume stimuli always override osmotic stimuli.The absence or presence of AVP is the major physiologic determinant of urinary free water excretion or retention. AVP acts principally on renal collecting tubules to increase water reabsorption. The antidiuretic effects of AVP are mediated by V2 vasopressin receptors. AVP can also increase vascular resistance through stimulation of V1 receptors.
Diabetes insipidus (DI) is characterized by the inability to appropriately concentrate urine in response to volume and osmotic stimuli. The main causes for DI are decreased AVP production (central DI) or decreased renal response to AVP (nephrogenic DI).
AVP can also be secreted inappropriately in certain situations, particularly in elderly patients, leading to water retention and dilutional hyponatraemia. Inappropriate AVP secretion might be observed with central nervous system pathology, such as head injury, stroke, or cerebral tumour, or as a side effect of central acting drugs that interfere with the hypothalamic regulation or AVP. Noncentral causes of inappropriate AVP secretion include peripheral stimuli that mimic central vascular hypovolaemia, in particular severe low-output cardiac failure, and ectopic AVP secretion (usually by a bronchogenic carcinoma).
|Reference Ranges:||Values appropriate to osmolality (see chart provided with result).|
|Interpretation:||See Allergy testing General Information|
|Patient Preperation:||Patient lying down or seated for 30 minutes. Take parallel blood pressure, serum osmolality and full clinical details. Results for osmolalities should accompany the request sent to the referral laboratory.|
|Specimen Requirments:||Serum. Blood specimen in SST.(lithium heparin tube also acceptable).|
|Turnaround Time:||Assay is performed monthly, expected turnaround time within 6 weeks.|
|Referred Test:||Referred test|
|Location:||Royal Victoria Infirmary|