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Clin Biochem Rev [journal]
- Uncertainty in Measurement: A Review of Monte Carlo Simulation Using Microsoft Excel for the Calculation of Uncertainties Through Functional Relationships, Including Uncertainties in Empirically Derived Constants. [REVIEW]
- Clin Biochem Rev 2014 Feb; 35(1):37-61.
The Guide to the Expression of Uncertainty in Measurement (usually referred to as the GUM) provides the basic framework for evaluating uncertainty in measurement. The GUM however does not always provide clearly identifiable procedures suitable for medical laboratory applications, particularly when internal quality control (IQC) is used to derive most of the uncertainty estimates. The GUM modelling approach requires advanced mathematical skills for many of its procedures, but Monte Carlo simulation (MCS) can be used as an alternative for many medical laboratory applications. In particular, calculations for determining how uncertainties in the input quantities to a functional relationship propagate through to the output can be accomplished using a readily available spreadsheet such as Microsoft Excel. The MCS procedure uses algorithmically generated pseudo-random numbers which are then forced to follow a prescribed probability distribution. When IQC data provide the uncertainty estimates the normal (Gaussian) distribution is generally considered appropriate, but MCS is by no means restricted to this particular case. With input variations simulated by random numbers, the functional relationship then provides the corresponding variations in the output in a manner which also provides its probability distribution. The MCS procedure thus provides output uncertainty estimates without the need for the differential equations associated with GUM modelling. The aim of this article is to demonstrate the ease with which Microsoft Excel (or a similar spreadsheet) can be used to provide an uncertainty estimate for measurands derived through a functional relationship. In addition, we also consider the relatively common situation where an empirically derived formula includes one or more 'constants', each of which has an empirically derived numerical value. Such empirically derived 'constants' must also have associated uncertainties which propagate through the functional relationship and contribute to the combined standard uncertainty of the measurand.
- Genetic Insights into Cardiometabolic Risk Factors. [REVIEW]
- Clin Biochem Rev 2014 Feb; 35(1):15-36.
Many biochemical traits are recognised as risk factors, which contribute to or predict the development of disease. Only a few are in widespread use, usually to assist with treatment decisions and motivate behavioural change. The greatest effort has gone into evaluation of risk factors for cardiovascular disease and/or diabetes, with substantial overlap as 'cardiometabolic' risk. Over the past few years many genome-wide association studies (GWAS) have sought to account for variation in risk factors, with the expectation that identifying relevant polymorphisms would improve our understanding or prediction of disease; others have taken the direct approach of genomic case-control studies for the corresponding diseases. Large GWAS have been published for coronary heart disease and Type 2 diabetes, and also for associated biomarkers or risk factors including body mass index, lipids, C-reactive protein, urate, liver function tests, glucose and insulin. Results are not encouraging for personal risk prediction based on genotyping, mainly because known risk loci only account for a small proportion of risk. Overlap of allelic associations between disease and marker, as found for low density lipoprotein cholesterol and heart disease, supports a causal association, but in other cases genetic studies have cast doubt on accepted risk factors. Some loci show unexpected effects on multiple markers or diseases. An intriguing feature of risk factors is the blurring of categories shown by the correlation between them and the genetic overlap between diseases previously thought of as distinct. GWAS can provide insight into relationships between risk factors, biomarkers and diseases, with potential for new approaches to disease classification.
- Physiology and its Importance for Reference Intervals. [REVIEW]
- Clin Biochem Rev 2014 Feb; 35(1):3-14.
Reference intervals are ideally defined on apparently healthy individuals and should be distinguished from clinical decision limits that are derived from known diseased patients. Knowledge of physiological changes is a prerequisite for understanding and developing reference intervals. Reference intervals may differ for various subpopulations because of differences in their physiology, most obviously between men and women, but also in childhood, pregnancy and the elderly. Changes in laboratory measurements may be due to various physiological factors starting at birth including weaning, the active toddler, immunological learning, puberty, pregnancy, menopause and ageing. The need to partition reference intervals is required when there are significant physiological changes that need to be recognised. It is important that laboratorians are aware of these changes otherwise reference intervals that attempt to cover a widened inter-individual variability may lose their usefulness. It is virtually impossible for any laboratory to directly develop reference intervals for each of the physiological changes that are currently known, however indirect techniques can be used to develop or validate reference intervals in some difficult situations such as those for children. Physiology describes our life's journey, and it is only when we are familiar with that journey that we can appreciate a pathological departure.
- Erratum. [PUBLISHED ERRATUM]
- Clin Biochem Rev 2013 Nov; 34(3):145.
[This corrects the article on p. 96 in vol. 34.].
- In Search of Mechanisms Associated with Mesenchymal Stem Cell-Based Therapies for Acute Kidney Injury. [REVIEW]
- Clin Biochem Rev 2013 Nov; 34(3):131-144.
Acute kidney injury (AKI) is classically described as a rapid loss of kidney function. AKI affects more than 15% of all hospital admissions and is associated with elevated mortality rates. Although many advances have occurred, intermittent or continuous renal replacement therapies are still considered the best options for reversing mild and severe AKI syndrome. For this reason, it is essential that innovative and effective therapies, without side effects and complications, be developed to treat AKI and the end-stages of renal disease. Mesenchymal stem cell (MSC) based therapies have numerous advantages in helping to repair inflamed and damaged tissues and are being considered as a new alternative for treating kidney injuries. Numerous experimental models have shown that MSCs can act via differentiation-independent mechanisms to help renal recovery. Essentially, MSCs can secrete a pool of cytokines, growth factors and chemokines, express enzymes, interact via cell-to-cell contacts and release bioagents such as microvesicles to orchestrate renal protection. In this review, we propose seven distinct properties of MSCs which explain how renoprotection may be conferred: 1) anti-inflammatory; 2) pro-angiogenic; 3) stimulation of endogenous progenitor cells; 4) anti-apoptotic; 5) anti-fibrotic; 6) anti-oxidant; and 7) promotion of cellular reprogramming. In this context, these mechanisms, either individually or synergically, could induce renal protection and functional recovery. This review summarises the most important effects and benefits associated with MSC-based therapies in experimental renal disease models and attempts to clarify the mechanisms behind the MSC-related renoprotection. MSCs may prove to be an effective, innovative and affordable treatment for moderate and severe AKI. However, more studies need to be performed to provide a more comprehensive global understanding of MSC-related therapies and to ensure their safety for future clinical applications.
- The De Ritis Ratio: The Test of Time. [REVIEW]
- Clin Biochem Rev 2013 Nov; 34(3):117-130.
De Ritis described the ratio between the serum levels of aspartate transaminase (AST) and alanine transaminase (ALT) almost 50 years ago. While initially described as a characteristic of acute viral hepatitis where ALT was usually higher than AST, other authors have subsequently found it useful in alcoholic hepatitis, where AST is usually higher than ALT. These interpretations are far too simplistic however as acute viral hepatitis can have AST greater than ALT, and this can be a sign of fulminant disease, while alcoholic hepatitis can have ALT greater than AST when several days have elapsed since alcohol exposure. The ratio therefore represents the time course and aggressiveness of disease that would be predicted from the relatively short half-life of AST (18 h) compared to ALT (36 h). In chronic viral illnesses such as chronic viral hepatitis and chronic alcoholism as well as non-alcoholic fatty liver disease, an elevated AST/ALT ratio is predictive of long terms complications including fibrosis and cirrhosis. There are methodological issues, particularly whether or not pyridoxal phosphate is used in the transaminase assays, and although this can have specific effects when patient samples are deficient in this vitamin, these method differences generally have mild effects on the usefulness of the assays or the ratio. Ideally laboratories should be using pyridoxal phosphate supplemented assays in alcoholic, elderly and cancer patients who may be pyridoxine deplete. Ideally all laboratories reporting abnormal ALT should also report AST and calculate the De Ritis ratio because it provides useful diagnostic and prognostic information.
- Adrenal Diagnostics: An Endocrinologist's Perspective focused on Hyperaldosteronism. [REVIEW]
- Clin Biochem Rev 2013 Nov; 34(3):111-116.
The era of sophisticated high resolution imaging with the consequent identification of previously unrecognised adrenal masses (adrenal incidentalomas), has emphasised the need for an appropriate biochemical approach to define adrenal function. The focus of this testing is on catecholamines from the adrenal medulla (testing that has been rendered relatively straightforward by plasma metanephrine measurements) and the physiological corticosteroids, cortisol and aldosterone, synthesised by the adrenal cortex. The diagnosis of hypercortisolism remains a challenge and has been extensively reviewed. In the context of hypertension and an adrenal incidentaloma, the exclusion of hyperaldosteronism has an importance beyond simple blood pressure control. This review focuses on the recommended approaches to both the diagnosis of hyperaldosteronism and the characterisation of its aetiology. Monogenetic causes of mineralocorticoid hypertension are discussed as are recent developments with respect to both the molecular aetiology and the differential diagnosis of aldosterone-producing adenomas.
- On-the-Job Evidence-Based Medicine Training for Clinician-Scientists of the Next Generation. [REVIEW]
- Clin Biochem Rev 2013 Aug; 34(2):93-103.
Clinical scientists are at the unique interface between laboratory science and frontline clinical practice for supporting clinical partnerships for evidence-based practice. In an era of molecular diagnostics and personalised medicine, evidence-based laboratory practice (EBLP) is also crucial in aiding clinical scientists to keep up-to-date with this expanding knowledge base. However, there are recognised barriers to the implementation of EBLP and its training. The aim of this review is to provide a practical summary of potential strategies for training clinician-scientists of the next generation. Current evidence suggests that clinically integrated evidence-based medicine (EBM) training is effective. Tailored e-learning EBM packages and evidence-based journal clubs have been shown to improve knowledge and skills of EBM. Moreover, e-learning is no longer restricted to computer-assisted learning packages. For example, social media platforms such as Twitter have been used to complement existing journal clubs and provide additional post-publication appraisal information for journals. In addition, the delivery of an EBLP curriculum has influence on its success. Although e-learning of EBM skills is effective, having EBM trained teachers available locally promotes the implementation of EBM training. Training courses, such as Training the Trainers, are now available to help trainers identify and make use of EBM training opportunities in clinical practice. On the other hand, peer-assisted learning and trainee-led support networks can strengthen self-directed learning of EBM and research participation among clinical scientists in training. Finally, we emphasise the need to evaluate any EBLP training programme using validated assessment tools to help identify the most crucial ingredients of effective EBLP training. In summary, we recommend on-the-job training of EBM with additional focus on overcoming barriers to its implementation. In addition, future studies evaluating the effectiveness of EBM training should use validated outcome tools, endeavour to achieve adequate power and consider the effects of EBM training on learning environment and patient outcomes.
- Monitoring in Clinical Biochemistry. [REVIEW]
- Clin Biochem Rev 2013 Aug; 34(2):85-92.
Monitoring tests form an increasing proportion of the workload in clinical biochemistry and biochemists can help by providing clinicians with information about the variability and precision of tests, the time frame for pharmacodynamic stabilisation after a treatment change, and the frequency of testing. This paper outlines the phases of monitoring, and how to decide if monitoring is beneficial, which test to use for monitoring, when a change in the test result indicates a need for the change in treatment and the length of testing intervals. We conclude with some recommendations for biochemists for future areas of research and advice that can be given to clinicians.
- HbA1c as a Diagnostic Test for Diabetes Mellitus - Reviewing the Evidence. [REVIEW]
- Clin Biochem Rev 2013 Aug; 34(2):75-83.
The evidence base in support of HbA1c as a diagnostic test for diabetes mellitus is focused on predicting a clinical outcome, considered to be the pinnacle of the Stockholm Hierarchy applied to reference intervals and clinical decision limits. In the case of diabetes, the major outcome of interest is the long term microvascular complications for which a large body of data has been accumulated, leading to the endorsement of HbA1c for diagnosis in many countries worldwide, with some variations in cut-offs and testing strategies.