title: Comparison of bioimpedance spectroscopy and the Watson formula for measuring body volume in patients on peritoneal dialysis.
abstract: BACKGROUND
  Knowing total body volume (V) is crucial in patients on peritoneal dialysis (PD). It is usually calculated by the Watson anthropometric formula, although the use of bioimpedance spectroscopy (BIS) is becoming increasingly widespread. Measuring V with both methods can at times produce quite different results.
  
  
  OBJECTIVE
  We aimed to identify differences between the 2 forms of measuring volume in a PD unit and determine which clinical factors are associated with these differences.
  
  
  METHODS
  Ours is an observational study of 74 patients on PD. We measured V using BIS (Vbis) and the Watson formula (Vw); 271 measurements were made with each method. We calculated the difference between Vbis and Vw in each patient and classified them into 2 groups: Difference between volumes ≥10% or <10% Vbis. We assessed the presence of several clinical parameters in our patients. We assessed whether there were any differences between Vbis and Vw (Student t-test). We determined whether there was any association between the difference in volumes and the presence of the clinical parameters analysed (chi square test).
  
  
  RESULTS
  V was 2.15 l higher measured by the Watson formula than with BIS (P<.01). In 58.67% of the measurements, the difference between Vbis and Vw was ≥10%. Significant differences were found when comparing the presence of difference between volumes and the presence or not of diabetes mellitus (DM) (p=0,03), hypertension (HTN) (p=0,036), hypoalbuminemia (p<0,01), hypoprealbuminemia (p<0,01), low phase angle at 50 Hz (p<0,01), high C reactive protein (p<0,01), obesity (p=0,027), E/I ratio (ratio between extracellular and intracellular water) ≥1 (p<0.01) and residual diuresis (p=0.029).
  
  
  CONCLUSIONS
  There are significant differences in the V of PD Unit patients when obtained by Watson formula or by BIS. A difference between the measurements is associated with the presence of DM, HTN, hypoalbuminaemia, obesity, malnutrition, inflammation, E/I ratio ≥1 and the absence of residual diuresis.
authors.affiliation: Servicio de Nefrología, Complejo Hospitalario y Universitario de Albacete, Albacete, España.
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Martínez Fernández
authors.affiliation: Servicio de Nefrología, Complejo Hospitalario y Universitario de Albacete, Albacete, España.
authors.forename: Agustín
authors.initials: A
authors.lastname: Ortega Cerrato
authors.affiliation: Servicio de Nefrología, Complejo Hospitalario y Universitario de Albacete, Albacete, España.
authors.forename: Lourdes
authors.initials: L
authors.lastname: de la Vara Iniesta
authors.affiliation: Servicio de Medicina Interna, Complejo Hospitalario Universitario de Albacete, Galera (Albacete), España.
authors.forename: Eva
authors.initials: E
authors.lastname: Oliver Galera
authors.affiliation: Servicio de Nefrología, Complejo Hospitalario y Universitario de Albacete, Albacete, España.
authors.forename: Carmen
authors.initials: C
authors.lastname: Gómez Roldán
authors.affiliation: Servicio de Nefrología, Complejo Hospitalario y Universitario de Albacete, Albacete, España. Electronic address: gonzalomfer@hotmail.com.
authors.forename: Juan
authors.initials: J
authors.lastname: Pérez Martínez
mesh_terms: D001823:Body Composition; D001834:Body Water; D017097:Electric Impedance; D006801:Humans; D009765:Obesity; D010530:Peritoneal Dialysis; D013057:Spectrum Analysis
keywords: Bioimpedance spectroscopy; Bioimpedancia espectroscópica; Diálisis peritoneal; Fórmula de Watson; Peritoneal dialysis; Total body volume; Volumen corporal total; Watson formula