[1] Royal Hallamshire Hosp, Dept Cardiol, Sheffield S10 2JF, S Yorkshire, England
[2] Univ Sheffield, Dept Human Metab & Clin Biochem, Sheffield, S Yorkshire, England
[3] Barnsley Dist Gen Hosp, Barnsley, S Yorkshire, England
[4] Univ Liverpool, Dept Clin Chem, Liverpool L69 3BX, Merseyside, England