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Investigations

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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General screening:

  • blood glucose, plasma calcium and potassium – hypercalcemia and hypokalemia can cause nephrogenic diabetes insipidus
  • serum sodium - may be raised
  • serum and urine osmolarity - plasma osmolality should be high and urine osmolality should be low. In cases of psychogenic polydipsia then generally the plasma osmolality is low
  • confirm existence of polyuria - more than 3.0 L urine in 24 hours

More specialist investigations:

  • fluid deprivation test with addition of exogenous vasopressin - usually, desmopressin
  • measurement of plasma ADH levels in response to hypertonic saline infusion in difficult cases
  • therapeutic trial of vasopressin - requires specialist supervision and indicated only if plasma ADH measurements are not available and the diagnosis is uncertain - 10 mcg per day given intranasally - cranial diabetes insipidus patients improve, nephrogenic diabetics are unchanged, primary polydipsia patients develop progressive hyponatraemia

References:

  1. Levy M, Prentice M, Wass J. Diabetes insipidus. BMJ. 2019 Feb 28;364:l321. doi: 10.1136/bmj.l321.

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