Clinical chemistry reference values for 75-year-old apparently healthy persons

Reference Intervals in Coagulation Analysis

Blood coagulation analysis is characterized by the application of a variety of materials, reagents, and analyzers for the determination of the same parameter, or analyte, by different laboratories worldwide. Accordingly, the application of common reference intervals, that, by definition, would represent a "range of values (of a certain analyte) that is deemed normal for a physiological measurement in healthy persons," is difficult to implement without harmonization of procedures. In fact, assay-specific reference intervals are usually established to allow for the discrimination of normal and abnormal values during evaluation of patient results. While such assay-specific reference intervals are often determined by assay manufacturers and subsequently adopted by customer laboratories, verification of transferred values is still mandatory to confirm applicability on site. The same is true for reference intervals that have been adopted from other laboratories, published information, or determined by indirect data mining approaches. In case transferable reference intervals are not available for a specific assay, a direct recruiting approach may or needs to be applied. In comparison to transferred reference interval verification, however, the direct recruiting approach requires a significantly higher number of well-defined samples to be collected and analyzed. In the present review, we aim to give an overview on the above-mentioned aspects and procedures, also with respect to relevant standards, regulations, guidelines, but also challenges for both, assay manufacturers and coagulation laboratories.

Reference Intervals for Platelet Counts in the Elderly: Results from the Prospective SENIORLAB Study

Currently, age- and sex-independent reference limits (RLs) are frequently used to interpret platelet counts in seniors. We aimed to define and validate reference intervals (RIs) for platelet counts within the framework of the prospective SENIORLAB study. Subjectively healthy Swiss individuals aged 60 years and older were prospectively included and followed for morbidity and mortality. Participants who had circumstances known to affect platelet counts were excluded. The obtained RIs were validated with indirect statistical methods. Frequencies of abnormal platelet counts in a population-based setting, including 41.5% of the entire age-specific population of the Principality of Liechtenstein, were compared by using age- and sex-independent RIs and the RLs obtained in the present study. For males (n = 542), 95% RIs for platelet counts were defined as follows: 150–300 × 10⁹/L (60–69 years); 130–300 × 10⁹/L (70–79 years); and 120–300 × 10⁹/L (80 years and above). For females (n = 661), the consolidated age-independent 95% RI was 165–355 × 10⁹/L. These RI values were validated by indirect RI determination of 51,687 (30,392 female/21,295 male) patients of the same age. Age- and sex-independent RIs exhibited imbalanced frequencies of abnormal platelet counts between the two sexes, which were corrected by introducing age- and sex-specific RLs. In conclusion, females have higher platelet counts than males. Whereas the upper RL for males remains constant, the lower RL decreases with age. We propose to abandon the practice of employing sex- and age-independent RL for platelet counts in the elderly.

Verification of reference intervals in routine clinical laboratories: practical challenges and recommendations

Reference intervals (RIs) are fundamental tools used by healthcare and laboratory professionals to interpret patient laboratory test results, ideally enabling differentiation of healthy and unhealthy individuals. Under optimal conditions, a laboratory should perform its own RI study to establish RIs specific for its method and local population. However, the process of developing RIs is often beyond the capabilities of an individual laboratory due to the complex, expensive and time-consuming process to develop them. Therefore, a laboratory can alternatively verify RIs established by an external source. Common RIs can be established by large, multicenter studies and can subsequently be received by local laboratories using various verification procedures. The standard approach to verify RIs recommended by the Clinical Laboratory Standards Institute (CLSI) EP28-A3c guideline for routine clinical laboratories is to collect and analyze a minimum of 20 samples from healthy subjects from the local population. Alternatively, "data mining" techniques using large amounts of patient test results can be used to verify RIs, considering both the laboratory method and local population. Although procedures for verifying RIs in the literature and guidelines are clear in theory, gaps remain for the implementation of these procedures in routine clinical laboratories. Pediatric and geriatric age-groups also continue to pose additional challenges in respect of acquiring and verifying RIs. In this article, we review the current guidelines/approaches and challenges to RI verification and provide a practical guide for routine implementation in clinical laboratories.

Biochemistry of the menopause

The life of a human female is characterized from teenage years by monthly menstruation which ceases (the menopause) typically between the age of 40 and 60 years. The potential for reproduction declines and ceases as the ovaries become depleted of follicles. A transition period in mid-life, for 2 to 10 years, when menstruation is less regular is called the perimenopause. The menopause is associated with a significant decline in plasma concentrations of sex hormones, an increase in the concentrations of the gonadotrophins and changes in other hormones such as the inhibins. These changes are superimposed with effects of aging, social and metabolic factors, daily activity and well-being. Although the menopause is entirely natural, in some cases ovarian failure can occur earlier than usual; this is pathological and warrants careful biochemical investigations to distinguish it from conditions causing infertility. Elderly females are affected by a range of clinical disorders including endocrine, cardiovascular, skeletal, urogenital tract and immunological systems, body mass, vasomotor tone, mood and sleep pattern. Reference intervals for many diagnostic biochemical tests for the menopause need to be used when interpreting results in clinical investigations for patient management. The standardization and harmonization of assays are being addressed. Many women now choose to develop their career before bearing children, and the health service has had to change services around this. This review does not cover screening for and tests during pregnancy. The review is timely since the population is aging and there will be more demand on healthcare services.

Reference intervals: current status, recent developments and future considerations

Reliable and accurate reference intervals (RIs) for laboratory analyses are an integral part of the process of correct interpretation of clinical laboratory test results. RIs given in laboratory reports have an important role in aiding the clinician in interpreting test results in reference to values for healthy populations. Since the 1980s, the International Federation of Clinical Chemistry (IFCC) has been proactive in establishing recommendations to clarify the true significance of the term 'RIs, to select the appropriate reference population and statistically analyse the data. The C28-A3 guideline published by the Clinical and Laboratory Standards Institute (CLSI) and IFCC is still the most widely-used source of reference in this area. In recent years, protocols additional to the Guideline have been published by the IFCC, Committee on Reference Intervals and Decision Limits (C-RIDL), including all details of multicenter studies on RIs to meet the requirements in this area. Multicentric RIs studies are the most important development in the area of RIs. Recently, the C-RIDL has performed many multicentric studies to obtain common RIs. Confusion of RIs and clinical decision limits (CDLs) remains an issue and pediatric and geriatric age groups are a significant problem. For future studies of RIs, the genetic effect would seem to be the most challenging area. 
The aim of the review is to present the current theory and practice of RIs, with special emphasis given to multicenter RIs studies, RIs studies for pediatric and geriatric age groups, clinical decision limits and partitioning by genetic effects on RIs.

Statistical methods used in the calculation of geriatric reference intervals: a systematic review

Geriatric reference intervals (RIs) are not commonly available and are rarely used. It is difficult to select a reference population from a cohort with a high degree of morbidity. Also important are the statistical approaches used to determine health-associated reference values. It is the aim of this study to examine the statistical methods used in the calculation of geriatric RIs.

A search was conducted on EMBASE and Medline for articles between January 1989 and January 2014. Studies were selected if they: 1) were English primary articles; 2) performed a clinical chemistry test on a blood fraction; 3) had a population sub-group consisting of individuals ≥65 years of age; and 4) calculated a RI for the subgroup ≥65 years of age.

There were 64 articles identified, of which 78.1% described the RI calculation method used. RI calculation was performed by non-parametric (21.9%), parametric (42.2%), robust (3.1%), or other (17.2%) methods. Outlier detection (SD, Grubb’s test, Tukey’s fence, Dixon) was infrequently used and although most studies performed partitioning, only 57.8% tested the statistical significance of the partitions. Few studies (17.2%) reported confidence intervals for the RI estimates. Overall, only 14.1% of studies provided RI estimates which followed the CLSI guideline EP28-A3c.

Statistical methods for RI calculation and partitioning varied considerably between studies and many failed to provide adequate descriptions of these methods. Challenges in analyses arose from insufficient sample sizes and heterogeneity in the elderly population. Geriatric RIs, although present in the literature, may not be properly calculated and should be carefully considered before applying them for clinical care.

Clinical use of conventional reference intervals in the frail elderly

RATIONALE, AIMS AND OBJECTIVES

Reference intervals provided by the laboratory are commonly established by measuring samples from apparently healthy subjects in the ages 18-65 years, excluding elderly individuals with chronic diseases and medication. The aim of our study was to establish whether current reference intervals for immune parameters and chemical biomarkers are valid for older individuals including those with chronic diseases, so-called frail elderly.

METHODS

Data from our cohort of 138 non-infected nursing home residents (NHR), mean age 86.8 years, range 80-98, were compared with raw data, as basis for the development of reference intervals, obtained from reference populations, like blood donors (IgA, IgG, IgM, C3 and C4) and from the Nordic Reference Interval Project (NORIP) (alanine aminotransferase, albumin, aspartate aminotransferase, creatinine, gamma-glutamyl transferase, lactate dehydrogenase, phosphate, sodium and urea). Immune parameters were measured by nephelometry and in NORIP the measurements were performed by means of different routine methods, in more than 100 laboratories.

RESULTS

Only nine individuals (7%) of NHR were found to be free from chronic disease. C3, C4 (P < 0.001) and IgG levels (P < 0.05) were higher, while IgM levels (P < 0.001) were lower in NHR compared with reference blood donors. Levels of alanine aminotransferase, phosphate (P < 0.001), albumin (P < 0.05) and sodium (P < 0.01) were lower while creatinine and urea levels were higher (P < 0.001) in NHR compared with NORIP subjects.

CONCLUSION

Comparing laboratory results from elderly people with conventional reference intervals can be misleading or even dangerous, as normal conditions may appear pathological, or vice versa and thus lead to unnecessary or even harmful treatment.

The theory of reference values: an unfinished symphony

The history of the theory of reference values can be written as an unfinished symphony. The first movement, allegro con fuoco, played from 1960 to 1980: a mix of themes devoted to the study of biological variability (intra-, inter-individual, short- and long-term), preanalytical conditions, standardization of analytical methods, quality control, statistical tools for deriving reference limits, all of them complex variations developed on a central melody: the new concept of reference values that would replace the notion of normality whose definition was unclear. Additional contributions (multivariate reference values, use of reference limits from broad sets of patient data, drug interferences) conclude the movement on the variability of laboratory tests. The second movement, adagio, from 1980 to 2000, slowly develops and implements initial works. International and national recommendations were published by the IFCC-LM (International Federation of Clinical Chemistry and Laboratory Medicine) and scientific societies [French (SFBC), Spanish (SEQC), Scandinavian societies…]. Reference values are now topics of many textbooks and of several congresses, workshops, and round tables that are organized all over the world. Nowadays, reference values are part of current practice in all clinical laboratories, but not without difficulties, particularly for some laboratories to produce their own reference values and the unsuitability of the concept with respect to new technologies such as HPLC, GCMS, and PCR assays. Clinicians through consensus groups and practice guidelines have introduced their own tools, the decision limits, likelihood ratios and Reference Change Value (RCV), creating confusion among laboratorians and clinicians in substituting reference values and decision limits in laboratory reports. The rapid development of personalized medicine will eventually call for the use of individual reference values. The beginning of the second millennium is played allegro ma non-troppo from 2000 to 2012: the theory of reference values is back into fashion. The need to revise the concept is emerging. The manufacturers make a friendly pressure to facilitate the integration of Reference Intervals (RIs) in their technical documentation. Laboratorians are anxiously awaiting the solutions for what to do. The IFCC-LM creates Reference Intervals and Decision Limits Committee (C-RIDL) in 2005. Simultaneously, a joint working group IFCC-CLSI is created on the same topic. In 2008 the initial recommendations of IFCC-LM are revised and new guidelines are published by the Clinical and Laboratory Standards Institute (CLSI C28-A3). Fundamentals of the theory of reference values are not changed, but new avenues are explored: RIs transference, multicenter reference intervals, and a robust method for deriving RIs from small number of subjects. Concomitantly, other statistical methods are published such as bootstraps calculation and partitioning procedures. An alternative to recruiting healthy subjects proposes the use of biobanks conditional to the availability of controlled preanalytical conditions and of bioclinical data. The scope is also widening to include veterinary biology! During the early 2000s, several groups proposed the concept of 'Universal RIs' or 'Global RIs'. Still controversial, their applications await further investigations. The fourth movement, finale: beyond the methodological issues (statistical and analytical essentially), important questions remain unanswered. Do RIs intervene appropriately in medical decision-making? Are RIs really useful to the clinicians? Are evidence-based decision limits more appropriate? It should be appreciated that many laboratory tests represent a continuum that weakens the relevance of RIs. In addition, the boundaries between healthy and pathological states are shady areas influenced by many biological factors. In such a case the use of a single threshold is questionable. Wherever it will apply, individual reference values and reference change values have their place. A variation on an old theme! It is strange that in the period of personalized medicine (that is more stratified medicine), the concept of reference values which is based on stratification of homogeneous subgroups of healthy people could not be discussed and developed in conjunction with the stratification of sick patients. That is our message for the celebration of the 50th anniversary of Clinical Chemistry and Laboratory Medicine. Prospects are broad, enthusiasm is not lacking: much remains to be done, good luck for the new generations!

Bone marrow: the workhorse organ

Bone marrow accounts for 3% to 6% of body weight and is dispersed throughout bone. In a healthy adult, bone marrow produces approximately 500 billion new blood cells daily to maintain steady-state levels in the peripheral circulation. Its output is measured using the complete blood count (CBC), which is arguably the most frequently ordered laboratory test in the clinical milieu. Hematopoiesis starts with hematopoietic stem cells that differentiate and mature into any of the three different types of mature blood cells. A simple CBC can rule out, confirm, or direct attention to anemia, cancer, infection, acute hemorrhage states, toxin exposure, allergies, immunodeficiencies, or adverse drug reactions. Interpreting CBCs depends on reference values from the laboratory that processes the blood sample. Since reference intervals are formulated based on a younger, much healthier population, data specific to elderly people are limited.

Interpreting routine biochemistry in those aged over 65 years: a time for change

In clinical practice, routine biochemistry tests are often performed for diagnostic or screening purposes. We reviewed papers that have reported reference values for people older than 65 years with or without overt health problems. Wider intervals have generally been reported for sodium, potassium, calcium and C-reactive protein (CRP) in the elderly. Higher levels of creatinine and lower levels of total cholesterol (TC) and serum albumin (SA) are observed with ageing. Elderly people have been found to be at greater risk for overt abnormalities in sodium, potassium, creatinine, TC, SA and CRP. The consequences of these abnormalities could be severe. For instance, even mild hyponatremia was associated with increased risk of mortality, disability and myocardial infarction. Mild hypernatremia was associated with severe disability. Mild increases in CRP levels were associated with an increased risk of sarcopenia, disability, cardiovascular disease and cognitive decline. Mild decreases in TC levels were associated with an increased risk of disability or mortality, and mild decreases in SA were associated with an increased risk of mortality, disability, sarcopenia and frailty. Nutritional factors could not wholly explain these effects. Modified biochemical reference values are required for elderly patients, as biochemical results can serve as markers of vulnerability to age-related diseases, linked to metabolism. Careful diagnosis and corrective interventions are needed for patients in this age group.

[Interpretation of laboratory results of elderly subjects: effect of age or aging]

The clinical pertinence of laboratory tests is conditioned by the use of well-documented databases on biological variability. Knowledge of these variations in the pediatric and adolescent population is well established. On the other hand, the situation is not so obvious for the elderly population. This population is generally not homogeneous and well-defined physiological variations are scarce. The observed variations generally reflect infraclinical or chronic illnesses. Interindividual variation is generally higher in the elderly population than in younger subjects. Thus, it would be more judicious to classify older persons as a function of their functional performance. This raises the issue of the proper definition of "good health" during the aging process. The criteria usually used for young adults should be revisited. The relationship with age is in fact variable from one assay to another: sometimes low, non significant or on contrary extremely wide. Well-adapted reference intervals are a prerequisite to proper interpretation of laboratory data in the elderly population. In some instances however, reference limits may be unsuitable, e.g. when the biological variability is too large, reference limits used for younger adults should be applied, while in other cases, traditional reference limits must be applied for decision-making limits.

Genetic risk factors and markers for Alzheimer's disease and/or depression in the VITA study

OBJECTIVES

In ageing population, both Alzheimer's disease (AD) and depression are common. Significant depressive symptoms are often co-morbid with cognitive impairment and dementia. In this study, we attempted to find various factors and markers for both AD and depression in a longitudinal cohort, the Vienna-Transdanube-Aging (VITA)-study.

METHODS

The VITA-Study consisted of 305 healthy subjects, 174 subjects with depression only, 55 subjects diagnosed with AD only and 72 subjects with depression as well as AD. Associations between AD and/or depression to gene polymorphisms APO E (epsilon4), choline acetyltransferase (ChAT) 4G to A, serotonin-transporter gene promoter-length, dopamine-D4-receptor, ciliary-neurotrophic-factor-null mutation and brain-derived neurotrophic factor (C270T) and to various known factors were analyzed.

RESULTS

AD and depression were significant associated. Significant risk factors found for AD were low education, low folic acid and depressive-symptoms, while for depression were low education and higher nonsteroidal anti-inflammatory drugs (NSAID) consume. Moreover, the ChAT polymorphism associated significant to depression. Gender, education, and ChAT significantly associated with the combination AD and/or depression.

CONCLUSION

Such studies must be conducted cautiously, as co-morbidities and gene-environmental-social influences may sway the results dramatically. We found in the VITA-study significant association between depression and AD and between ChAT polymorphism and depression.