Decline in Renal Concentration Ability in Lithium Treated Patients

Inclusion Criteria: * included in the previous study * men and women * age ≥ 18 years Exclusion Criteria: * General contra-indications for participation in a trial: * inability to give informed consent * pregnancy * unstable psychiatric condition * Alternative causes of (nephrogenic) diabetes insipidus: * hypokalemia (plasma potassium \< 3.0 mmol/l) * severe hypercalcemia (albumin-corrected plasma calcium \> 2.80 mmol/l) * hyperglycemia (plasma glucose \> 10.0 mmol/l) * history of amyloidosis, Sjögren's syndrome or Sickle cell anemia * previous treatment with ifosfamide * established primary polydipsia or central diabetes insipidus * Contra-indications for dDAVP administration: * inability to comply with water restriction * renal insufficiency (GFR \< 45 ml/min/1.73 m2) * hyponatremia (plasma sodium \< 130 mmol/l) * instable angina pectoris * decompensated cardial insufficiency * Other: * concomitant treatment with desmopressin or democlocycline