quality assurance programs that aim to reduce inter- laboratory differences (2-4). Results from these qual- ity assurance programs verify that there are good interlaboratory agreements for high-volume labora- tory markers. It should thus be possible to have common reference intervals, independent of the lab- oratory that performs the test. Increasing inter- national communication between health care providers also increases the need for harmonization of laboratory test results including reference intervals (5). Several groups are presently establishing com- mon reference values (6,7). Many biomarkers change with age, and reference values based on a population in the age range 20–50 years may thus not be appropriate for 75-year-old patients. We have previously reported reference values from this study cohort at the age of 70 (8). Since appro- priate reference values are essential for quality patient care, we felt an urge to reinvestigate reference values for our most widely used serum analytes at the age of 75. The criteria for deﬁning a ‘healthy’ population used to establish reference values vary. If very strict criteria are used in an elderly population the group may become very small and not really representative of the whole population. Many elderly individuals are treated with some type of medication and often have had symptoms of cardiovascular disease (CVD). When we set up the selection criteria for this study we decided to exclude all individuals with diabetes mellitus and then calculate reference values both for the whole group and for the subgroup without a history of CVD to be able to compare them with each other. Materials and methods Subjects Eligible were all subjects aged 70 living in the com- munity of Uppsala, Sweden. The subjects were cho- sen from the register of community living and were invited in a randomized order from the start of the study in April 2001 to the last-included subject in June 2005. The subjects received an invitation letter within 1 month of their 70th birthday in order to standardize for age. Of the 2025 subjects invited, 1016 subjects were investigated giving a participation rate of 50.1%. The study is part of the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (9). These subjects were reinvestigated at age 75. At the reinvestigation, 821 participated and provided blood samples. Blood samples were collected in Vacutainer tubes without additives. After clotting, the samples Reference values 265 were centrifugated, and the sera were collected and frozen at –80 C. The study was approved by the Ethics Committee of the University of Uppsala, and the participants gave informed consent prior to blood sampling. The study was performed in accordance with the ethical rules for human experimentation that are stated in the Declaration of Helsinki. Baseline investigation The participants were asked to answer a questionnaire about their medical history, smoking habits, and regular medication. All subjects were investigated in the morning after an overnight fast. No medication or smoking was allowed after midnight. During the investigation, the subjects were supine in a quiet room maintained at a constant temperature. CVD was deﬁned as myocardial infarction, stroke, and heart failure, but not hypertension. Instrument Serum alanine aminotransferase (ALT) (EC 2.6.1.2, reagent: 1655281), albumin (reagent: 8196057), alka- line phosphatase (EC 3.1.3.1, reagent: 1053180), apolipoprotein A1 (reagent: 6801737), apolipopro- tein B (reagent: 6801738), bilirubin (reagent: 8383051), calcium (reagent: 1450261), chloride (reagent: 8445207), cholesterol (reagent: 1669829), creatinine (reagent: 8141947), creatine kinase (reagent: 8479396), C-reactive protein (reagent: CRP Vario , Abbott Laboratories, Abbott Park, IL, USA), direct HDL-cholesterol (reagent: 6801895), g-glutamyltransferase (GGT) (EC 2.3.2.2, reagent: 8257289), iron (reagent: 1515808), lactate dehydro- genase (LDH) (reagent: 838489), pancreatic lipase (EC 3.1.1.3, reagent: 1668409), magnesium (reagent: 825593), phosphate (reagent: 1513209), potassium (reagent: 8157596), sodium (reagent: 8379034), transferrin (reagent: 6801767), triglycerides (reagent: 1336544), uric acid (reagent: 1943927), and urea (reagent: 8102204) measurements were performed on an Ortho Vitros FS 5.1 (Ortho Clinical Diagnos- tics, Rochester, NY, USA) and reported using SI units. If not stated otherwise within the brackets, the reagents were all obtained from Ortho Clinical Diagnostics. The assays were performed at the depart- ment of Clinical Chemistry, Kalmar, Sweden. The laboratory is accredited by Swedac (Borås, Sweden) according to ISO 17025. The assays are included in the Swedish laboratory external quality assurance program managed by Equalis (Uppsala, Sweden). The total analytical imprecision of the assays is pre- sented in Table I, and the traceability of the methods is presented in Table II. From the test results the