Diabetes insipidus laboratory findings: Difference between revisions
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==Laboratory Findings== | ==Laboratory Findings== | ||
In order to distinguish DI from other causes of excess urination, [[blood glucose]], [[bicarbonate]] and [[calcium]] need to be tested. Measurement of blood [[electrolyte]]s can reveal a high [[sodium]] level ([[hypernatremia]] as [[dehydration]] develops). [[Urinalysis]] demonstrates a dilute urine with a low [[specific gravity]]. Urine [[osmolality]] and electrolyte levels are typically low. | In order to distinguish DI from other causes of excess urination, [[blood glucose]], [[bicarbonate]] and [[calcium]] need to be tested. Measurement of blood [[electrolyte]]s can reveal a high [[sodium]] level ([[hypernatremia]] as [[dehydration]] develops). [[Urinalysis]] demonstrates a dilute urine with a low [[specific gravity]]. Urine [[osmolality]] and electrolyte levels are typically low. | ||
A ''fluid deprivation test'' helps determine whether DI is caused by: | A '''fluid deprivation test''' helps determine whether DI is caused by: | ||
# excessive intake of fluid | # excessive intake of fluid | ||
# a defect in [[antidiuretic hormone|ADH]] production | # a defect in [[antidiuretic hormone|ADH]] production | ||
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If central DI is suspected, testing of other hormones of the [[pituitary]], as well as [[magnetic resonance imaging]] (MRI), is necessary to discover if a disease process (such as a [[prolactinoma]], or [[histiocytosis]], [[syphilis]], [[tuberculosis]] or other [[tumor]] or [[granuloma]]) is affecting pituitary function. | If central DI is suspected, testing of other hormones of the [[pituitary]], as well as [[magnetic resonance imaging]] (MRI), is necessary to discover if a disease process (such as a [[prolactinoma]], or [[histiocytosis]], [[syphilis]], [[tuberculosis]] or other [[tumor]] or [[granuloma]]) is affecting pituitary function. | ||
Habit drinking (in its severest form termed [[psychogenic polydipsia]]) is the most common imitator of diabetes insipidus at all ages. While many adult cases in the medical literature are associated with mental disorders, most patients with habit polydipsia have no other detectable disease. The distinction is made during the water deprivation test, as some degree of urinary concentration above isosmolar is usually obtained before the patient becomes dehydrated. | Habit drinking (in its severest form termed [[psychogenic polydipsia]]) is the most common imitator of diabetes insipidus at all ages. While many adult cases in the medical literature are associated with mental disorders, most patients with habit polydipsia have no other detectable disease. The distinction is made during the water deprivation test, as some degree of urinary concentration above isosmolar is usually obtained before the patient becomes dehydrated. | ||
==References== | ==References== | ||
{{reflist|2}} | {{reflist|2}} | ||
Revision as of 20:19, 28 September 2012
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Laboratory Findings
In order to distinguish DI from other causes of excess urination, blood glucose, bicarbonate and calcium need to be tested. Measurement of blood electrolytes can reveal a high sodium level (hypernatremia as dehydration develops). Urinalysis demonstrates a dilute urine with a low specific gravity. Urine osmolality and electrolyte levels are typically low. A fluid deprivation test helps determine whether DI is caused by:
This test measures changes in body weight, urine output, and urine composition when fluids are withheld. Sometimes measuring blood levels of ADH during this test is also necessary. To distinguish between the main forms, desmopressin stimulation is also used; desmopressin can be taken by injection, a nasal spray, or a tablet. While taking desmopressin, a patient should drink fluids or water only when thirsty and not at other times, as this can lead to sudden fluid accumulation in central nervous system. If desmopressin reduces urine output and increases osmolarity, the pituitary production of ADH is deficient, and the kidney responds normally. If the DI is due to renal pathology, desmopressin does not change either urine output or osmolarity. If central DI is suspected, testing of other hormones of the pituitary, as well as magnetic resonance imaging (MRI), is necessary to discover if a disease process (such as a prolactinoma, or histiocytosis, syphilis, tuberculosis or other tumor or granuloma) is affecting pituitary function. Habit drinking (in its severest form termed psychogenic polydipsia) is the most common imitator of diabetes insipidus at all ages. While many adult cases in the medical literature are associated with mental disorders, most patients with habit polydipsia have no other detectable disease. The distinction is made during the water deprivation test, as some degree of urinary concentration above isosmolar is usually obtained before the patient becomes dehydrated.