title: Quantitating nocturia: a study into the recording of solute and water excretion to determine causation.
abstract: BACKGROUND
  Nocturia is common but the clinical assessment of its severity and cause rarely involves any biochemical analysis. Investigating the cause of nocturia needs to be informed by the overall 24 h fluid and solute excretion patterns. The aim of this study was to establish a practical method of monitoring the renal excretion of water and solutes over a complete 24 h cycle.
  
  
  METHODS
  The excretion patterns of sodium, volume and osmoles were assessed in 89 healthy control subjects over a 24 h period by sampling each voiding from the 24 h collection and then using the total urine creatinine as the denominator. A group of 21 patients under investigation for sleep-disordered breathing (SDB: a group of disorders known to increase the risk of nocturia) were also studied to determine comparative excretion patterns.
  
  
  RESULTS
  Reference excretion patterns of sodium, volume and osmoles were described. Patients under investigation for SDB had overall a significant (P < 0.001) increase in urine sodium excretion at night (nocturnal natriuresis) matched by an increased osmotic excretion and accompanied by a significantly increased nocturnal urine volume (P < 0.001).
  
  
  CONCLUSIONS
  Breaking down a 24 h urine collection into voided aliquots provides practical information on the pattern of water and solute excretion. Such patterns may assist in identifying the underlying mechanism of significant nocturia in individual patients presenting with this symptom, and could be used as a method of monitoring treatment.
authors.affiliation: Department of Clinical Biochemistry, Royal Gwent Hospital, Newport NP20 2UB, UK.
authors.forename: Philip
authors.initials: P
authors.lastname: Waters
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Hack
authors.forename: Jeanette
authors.initials: J
authors.lastname: Richards
authors.forename: Michael D
authors.initials: MD
authors.lastname: Penney
mesh_terms: D000328:Adult; D003404:Creatinine / Q000652:urine; D005260:Female; D006801:Humans; D007668:Kidney / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods*; D053158:Nocturia / Q000175:diagnosis* / Q000209:etiology* / Q000503:physiopathology; D011188:Potassium / Q000652:urine; D012891:Sleep Apnea Syndromes / Q000652:urine; D012964:Sodium / Q000652:urine; D016482:Urinalysis / Q000379:methods*; D014554:Urination
chemical_list: D012964:Sodium; D003404:Creatinine; D011188:Potassium