Reference values 267 Table II. Traceability of standardizations of methods used to calculate the reference intervals. Table III. Basic characteristics for the persons included in the reference material (n = 727). Alanine aminotransferase (ALT) Albumin Alkaline phosphatase Apolipoprotein A1 Apolipoprotein B Bilirubin Calcium Chloride Cholesterol Creatinine Creatine kinase C-reactive protein (CRP) Glucose g-Glutamyltransferase (GGT) HDL-cholesterol Iron Lactate dehydrogenase (LDH) Magnesium Phosphate Potassium Sodium Transferrin Triglycerides Urate Urea IFCC reference method NIST SRM 927c IFCC reference method WHO-IFCC RR SP1-01 WHO-IFCC RR SP3-08 NIST SRM 916a NIST SRM 915a NIST SRM 919a NIST 911b NIST, SRM914 Scandinavian Committee on Enzymes IRMM/IFCC CRM 470 Isotope dilution mass spectrometry (IDMS) IFCC reference method NIST SRM 911b NIST SRM 937 Pyruvate-to-lactate total lactate dehydrogenase method NIST SRM 929 NIST SRM 200 NIST SRM 918a NIST SRM 919a IRMM/IFCC CRM 470 CDC reference method NIST SRM 913a NIST SRM 912a in the Appendix (12,13, (available online at http:// www.informahealthcare.com/doi/abs/10.3109/03009 734.2011.644873)). Mann–Whitney tests comparing males and females with and without CVD At a P level of 0.01 only urate (P = 0.00008) showed signiﬁcant differences between males with and with- out CVD. Despite the signiﬁcant difference between males with and without CVD, the calculated reference interval after exclusion of individuals with CVD were within the 90% conﬁdence interval of the reference interval calculated with individuals including CVD. At the same signiﬁcance level, cholesterol (P = 0.0006), CRP (P < 0.0001), transferrin (P = 0.006), and apolipoprotein ratio (P = 0.0001) showed signiﬁcant differences between females with Females/ males (number) Height (cm) Weight (kg) Waist circumfer- ence (cm) BMI (kg/m2) Waist/hip ratio DBP (mmHg) SBP (mmHg) Females, median (IQR) 373 161 (157–165) 69 (60–78) 91 (82–98) 26.3 (23.4–29.4) 0.91 (0.87–0.97) 76 (70–80) 150 (140–164) Males, median (IQR) 354 175 (172–180) 79 (73–88) 93 (86–102) 26.1 (24.0–28.5) 0.97 (0.92–1.01) 76 (70–84) 146 (134–158) BMI = body mass index; DBP = diastolic blood pressure; SBP = systolic blood pressure. and without CVD. However, the reference intervals for these markers after exclusion of females with CVD were still within the 90% conﬁdence interval of the corresponding reference interval for all females. Discussion The deﬁnition of appropriate reference values is an important responsibility for clinical laboratories. The task of creating well deﬁned and accurate reference intervals is often costly and time-consuming compared to validating reference values provided by the assay manufacturer. However, such reference intervals often lack individuals older than 60–65 years of age. Following the recommendations of the International Federation of Clinical Chemistry, we have established reference values based on 75-year-old healthy males and females for a group of common serum analytes. The study population was recruited in the county of Uppsala, Sweden, and we have previously reported normal values for this cohort at the age of 70 (8). As the number of individuals with cardiovascular disease (CVD) increases with age and the prevalence of CVD in elderly populations can be very high, it could be debated whether individuals with CVD should be included or not. Exclusion of a large fraction of individuals when calculating a reference interval is not optimal as it may induce a bias when using the results for comparison with patients. However, CVD is a hetero- geneous group, and in most cases a history of CVD should not affect the biomarkers used in this study. We thus decided to include individuals with CVD in the reference material and then calculate reference values with and without individuals with CVD. Mann–Whit- ney tests comparing the groups with and without CVD showed that there were few signiﬁcant differences