title: Detection of sCD21 in Human Blood Using ELISA is Influenced by Ethylenediaminetetraacetic Acid (EDTA) Containing Blood Collection Tubes.
abstract: BACKGROUND
  CD21 is a 145 kDa membrane glycoprotein expressed mainly on B-cells and follicular dendritic cells. It is involved in activation, survival and proliferation of B-cells. CD21 can be cleaved to give soluble CD21 (sCD21), which is constantly shed in healthy people whereas the level of sCD21 is low in patients suffering from various autoimmune diseases.
  
  
  METHODS
  Blood was collected from 12 healthy donors into Heparin, EDTA and gel-separation tubes. Furthermore, plasma from 6 healthy donors was combined and EDTA or EGTA was subsequently added to analyze its influence on sCD21 levels measured by ELISA.
  
  
  RESULTS
  Differences in sCD21 levels were observed dependent on blood collection tubes used. sCD21 levels measured by ELISA were significantly higher if heparin/gel containing tubes were used compared to EDTA blood collection tubes. Upon addition of EDTA/EGTA to plasma drawn using Heparin blood collection tubes, sCD21 levels decrease to amounts found in EDTA-containing blood collection tubes suggesting calcium as the responsible factor rather than magnesium.
  
  
  CONCLUSIONS
  EDTA influences sCD21 levels determined by ELISA and therefore sCD21 measurements should be carried out using one type of blood collection tube throughout the experiment/medical examination.
authors.forename: Karl
authors.initials: K
authors.lastname: Linke
authors.forename: Harald
authors.initials: H
authors.lastname: Illges
mesh_terms: D000328:Adult; D004492:Edetic Acid / Q000737:chemistry*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D004864:Equipment and Supplies; D005260:Female; D006801:Humans; D008297:Male; D017464:Receptors, Complement 3d / Q000097:blood*; D013048:Specimen Handling; D055815:Young Adult
chemical_list: D017464:Receptors, Complement 3d; D004492:Edetic Acid