title: Simultaneous, noninvasive, and transdermal extraction of urea and homocysteine by reverse iontophoresis.
abstract: BACKGROUND
  Cardiovascular and kidney diseases are a global public health problem and impose a huge economic burden on health care services. Homocysteine, an amino acid, is associated with coronary heart disease, while urea is a harmful metabolic substance which can be used to reflect kidney function. Monitoring of these two substances is therefore very important. This in vitro study aimed to determine whether homocysteine is extractable transdermally and noninvasively, and whether homocysteine and urea can be extracted simultaneously by reverse iontophoresis.
  
  
  METHODS
  A diffusion cell incorporated with porcine skin was used for all experiments with the application of a direct current (dc) and four different symmetrical biphasic direct currents (SBdc) for 12 minutes via Ag/AgCl electrodes. The dc and the SBdc had a current density of 0.3 mA/cm(2).
  
  
  RESULTS
  The SBdc has four different phase durations of 15 sec, 30 sec, 60 sec, and 180 sec. It was found that homocysteine can be transdermally extracted by reverse iontophoresis. Simultaneous extraction of homocysteine and urea by reverse iontophoresis is also possible.
  
  
  CONCLUSIONS
  These results suggest that extraction of homocysteine and urea by SBdc are phase duration-dependent, and the optimum mode for simultaneous homocysteine and urea extraction is the SBdc with the phase duration of 60 sec.
authors.affiliation: Graduate Institute of Biomedicine and Biomedical Technology, National Chi Nan University, Nantou, Taiwan.
authors.forename: Congo Tak-Shing
authors.initials: CT
authors.lastname: Ching
authors.forename: Tzong-Ru
authors.initials: TR
authors.lastname: Chou
authors.forename: Tai-Ping
authors.initials: TP
authors.lastname: Sun
authors.forename: Shiow-Yuan
authors.initials: SY
authors.lastname: Huang
authors.forename: Hsiu-Li
authors.initials: HL
authors.lastname: Shieh
mesh_terms: D000818:Animals; D002318:Cardiovascular Diseases / Q000175:diagnosis; D006710:Homocysteine / Q000032:analysis / Q000302:isolation & purification*; D006801:Humans; D066298:In Vitro Techniques; D007478:Iontophoresis / Q000295:instrumentation / Q000379:methods*; D007674:Kidney Diseases / Q000175:diagnosis; D050997:Nanomedicine; D012867:Skin / Q000737:chemistry*; D013552:Swine; D014508:Urea / Q000032:analysis / Q000302:isolation & purification*
chemical_list: D006710:Homocysteine; D014508:Urea