title: A patient with a high concentration of B-type natriuretic peptide (BNP) but normal N-terminal proBNP concentration: A case report.
abstract: OBJECTIVE
  A 61-year-old female presented with non-typical chest pain. High levels of plasma B-type natriuretic peptide (BNP; result 3188 ng/L, reference range<100 ng/L, method Abbott Architect) were found, although she did not exhibit dyspnoea or other clinical symptoms of heart failure. Echocardiography did not provide an explanation for the elevated BNP concentrations. In follow-up, the chest pain complaints disappeared but BNP remained elevated at the same levels. The serum N-terminal proBNP (NT-proBNP) concentration appeared to be normal. This led us to doubt the accuracy of the BNP values.
  
  
  METHODS
  Possible interference was investigated with BNP and NT-proBNP assays from different manufacturers, various (auto)antibody tests, sample dilutions, addition of mouse serum and polyethylene glycol (PEG) precipitation.
  
  
  RESULTS
  BNP and NT-proBNP concentrations were normal when measured using all other (NT-pro)BNP immunoassays. Serial dilutions of sample and addition of mouse serum did not alter the results. Specific (auto)antibody tests were negative. However, PEG precipitation showed the presence of a high molecular weight immunoreactive protein.
  
  
  CONCLUSIONS
  We report a false positive BNP result possibly caused by a macro-BNP. This macro-BNP was only immunoreactive in the Abbott Architect BNP immunoassay. Clinicians should be aware of analytical interference when BNP results are constantly elevated in the absence of (non)cardiac causes.
authors.affiliation: Laboratory of Clinical Chemistry and Hematology, Viecuri Medical Centre, Venlo, The Netherlands. Electronic address: marceljanssen@viecuri.nl.
authors.forename: Marcel J W
authors.initials: MJ
authors.lastname: Janssen
authors.affiliation: Laboratory of Clinical Chemistry and Hematology, Viecuri Medical Centre, Venlo, The Netherlands.
authors.forename: Mathieu H
authors.initials: MH
authors.lastname: Velmans
authors.affiliation: Department of Cardiology, Viecuri Medical Centre, Venlo, The Netherlands.
authors.forename: Wilfred F
authors.initials: WF
authors.lastname: Heesen
mesh_terms: D005260:Female; D006801:Humans; D008875:Middle Aged; D020097:Natriuretic Peptide, Brain / Q000097:blood*; D020033:Protein Isoforms / Q000097:blood*
chemical_list: D020033:Protein Isoforms; D020097:Natriuretic Peptide, Brain
keywords: B-type natriuretic peptide (BNP); Immunoassay; Interference; Macro-BNP; Polyethylene glycol (PEG) precipitation