[1] Nordland Hosp, Dept Med, Prinsens Gate 164, N-8005 Bodo, Norway
[2] Arctic Univ Norway, Dept Clin Med, Tromso, Norway
[3] Univ Oslo, Gen Practice Res Unit AFE, Oslo, Norway
[4] Univ Hosp North Norway, Clin Res Dept, Oslo, Norway
[5] Stavanger Univ Hosp, Dept Med, Stavanger, Norway
[6] Haraldsplass Deaconess Hosp, Norwegian Qual Improvement Lab Examinat, Bergen, Norway
[7] Univ Bergen, Dept Publ Hlth & Primary Hlth Care, Bergen, Norway
[8] Haukeland Hosp, Dept Clin Biochem, Bergen, Norway
[9] Univ Oslo, Inst Clin Med, Oslo, Norway
[10] Oslo Univ Hosp, Dept Endocrinol Morbid Obes & Prevent Med, Oslo, Norway