Circulating levels and assessment of clinical laboratory analytes, in >80-year-old, apparently healthy, moderately healthy, and frail individuals

Blood samples are often used to investigate the possible presence of disease and to make treatment decisions. In the interpretation of the results, comparison either with previous values from the same individual or with a set of appropriate group-based reference intervals are used. Current reference intervals for common laboratory analytes are often based on measurements from apparently healthy persons aged 18–65 years. Age is accompanied by a general decline in organ functions and it is difficult to determine whether a change in levels of laboratory analytes in an elderly individual can be attributed to age alone, independent of environmental or disease processes. Frailty can be seen as a consequence of age-related multifactorial deterioration – physical, cognitive and sensory – resulting in vulnerability and lack of adaptability to internal stressors such as infection or new medication and/or external stressors such as fall at home. Consensus about the definition of “frail” and “frailty” is missing, both nationally and internationally, the question arises whether different definitions of “frailty” affect the interpretation of analytes when comparing different groups of elderly. The overarching aim of the thesis was to interpret and assess circulating levels of some clinical laboratory analytes in relation to conventional reference values in ≥80-year-old, “apparently healthy”, “moderately healthy”, and “frail” individuals. Data originated from other studies, in which blood samples were collected from individuals ≥80-year-old. Comparisons in Paper I of levels of some laboratory analytes, from 138 nursing home residents (NHRs), was made with blood from reference populations, both blood donor and the NORIP study. The results indicated differences for some immunological (complement factor 3 and 4, immunoglobulin G and M) and chemical analytes (alanine aminotransferase (ALT), phosphate, albumin, sodium, creatinine and urea), but no differences in levels occurred for aspartate aminotransferase (AST), gamma-glutamyltransferase (γ-GT) or lactate dehydrogenase (LDH). It was unclear whether the differences were due to differences in age between the elderly and the reference populations or whether the elderly individuals had chronic diseases and were on medication. In Paper II, 569 individuals elderly individuals ≥80 years old were classified as “healthy”, “moderately healthy”, and “frail”, based on diseases, medications and physical and cognitive abilities. Statis