title: Evaluation of adsorption of urine cystatin C to the polymer materials on the microplate by an antigen capture enzyme-linked immunosorbent assay.
abstract: BACKGROUND
  Cystatin C is a low molecular weight protein of 13 kDa with an isoelectric point of 9.3. Its adsorption on the urine sampling containers may cause the underestimation of cystatin C levels. We newly developed an antigen capture enzyme-linked immunosorbent assay (ELISA) of sandwich method for measurement of adsorbed level.
  
  
  METHODS
  We used a polystyrene microplates with 3 different polymers. These include high hydrophobic, low hydrophobic, and hydrophilic materials. Using the same microplate, the absorbed protein was measured by an antigen Capture ELISA, and calibration was conducted by an ordinary ELISA.
  
  
  RESULTS
  In normal urine the concentrations of absorbed cystatin C levels to the 3 materials at day 1 were 0.50, 0.32-0.84 microg/l (median, interquartile range), 0.28, 0.21-0.37 microg/l, and <0.08, <0.08-0.09 microg/l in high hydrophobic, low hydrophobic, and high hydrophilic material, respectively. The absorption rate was 6%, 3%, and 1%, respectively. The adsorption is dependent on urine pH. It changes reciprocally with urine protein concentration. In pathologic urine, the absolute absorption level was <0.08 microg/l on the median, and the adsorption ratio (absorption level/urine level) was much less than 0.5% of that in normal urine.
  
  
  CONCLUSIONS
  In the clinical setting, the absorption of cystatin C to sample containers is negligible since the rate of adsorption is low both in normal and pathologic urine. The material with high hydrophilic surface processing may be used for other proteins when interaction of the proteins with surface material affects the value to clinical decision.
authors.affiliation: Ikagaku CO., LTD., Kyoto, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Gotoh
authors.forename: Kazuo
authors.initials: K
authors.lastname: Uchida
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Hamano
authors.forename: Shinichi
authors.initials: S
authors.lastname: Mashiba
authors.forename: Isao
authors.initials: I
authors.lastname: Kawabata
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Itoh
mesh_terms: D000327:Adsorption; D000941:Antigens / Q000652:urine; D002138:Calibration; D055316:Cystatin C / Q000737:chemistry / Q000652:urine*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D011137:Polystyrenes / Q000737:chemistry
chemical_list: D000941:Antigens; D055316:Cystatin C; D011137:Polystyrenes