title: Why dried blood spots are an ideal tool for CYP1A2 phenotyping.
abstract: OBJECTIVE
  Dried blood spot (DBS) sampling has gained wide interest in bioanalysis during the last decade and has already been successfully applied in pharmacokinetic and phenotyping studies. However, all of the available phenotyping studies used small datasets and did not include a systematic evaluation of DBS-specific parameters. The latter is important since several of these factors still challenge the breakthrough of DBS in routine practice. In this study, caffeine and paraxanthine are determined in capillary DBS, venous DBS, whole blood and plasma for cytochrome P450 (CYP) 1A2 phenotyping. The aim of this study was to explore the usefulness of DBS as a tool for CYP1A2 phenotyping.
  
  
  METHODS
  A CYP1A2 phenotyping study was conducted in 73 healthy volunteers who received a 150 mg oral dose of caffeine. Six hours post-administration, caffeine and paraxanthine concentrations and paraxanthine:caffeine molar concentration ratios, i.e., the actual CYP1A2 phenotyping indices, were determined in capillary DBS (obtained by non-volumetric application, direct from the fingertip), venous DBS, whole blood, and plasma. Furthermore, the impact of DBS-specific parameters, including hematocrit, volume spotted, and punch location, was evaluated.
  
  
  RESULTS
  Concentrations of caffeine and paraxanthine in capillary DBS were, respectively, on average 12.7 and 13.8% lower than those in venous DBS and 31.5 and 33.1% lower than those in plasma. While these differences were statistically significant (p < 0.001), no significant difference was observed between the paraxanthine:caffeine molar ratios in the distinct evaluated matrices (p ≥ 0.053). This ratio also alleviated the impact of hematocrit and volume spotted.
  
  
  CONCLUSIONS
  Using the largest DBS-based phenotyping study to date, we have demonstrated that CYP1A2 phenotyping in capillary DBS is a valid and convenient alternative for the classical plasma-based approach. Additionally, we have provided an objective basis as to why DBS are an ideal tool for CYP1A2 phenotyping.
authors: Laboratory of Toxicology, Department of Bioanalysis, Faculty of Pharmaceutical Sciences, Ghent University, Harelbekestraat 72, 9000, Ghent, Belgium.
authors: Pieter M M
authors: PM
authors: De Kesel
authors: Willy E
authors: WE
authors: Lambert
authors: Christophe P
authors: CP
authors: Stove
mesh_terms: D000328:Adult; D002110:Caffeine / Q000008:administration & dosage / Q000097:blood* / Q000378:metabolism; D019388:Cytochrome P-450 CYP1A2 / Q000097:blood* / Q000378:metabolism; D059788:Dried Blood Spot Testing / Q000379:methods*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D012044:Regression Analysis; D013806:Theophylline / Q000097:blood; D055815:Young Adult
chemical_list: D002110:Caffeine; D013806:Theophylline; C504573:CYP1A2 protein, human; D019388:Cytochrome P-450 CYP1A2; C021183:1,7-dimethylxanthine