3As a Laboratory Medicine Specialists? DiagnosisPrognosisMonitoringScreeningAssessment of Risk
4Utility of the result of a measurement depends upon: The metrologyAn understanding of its relativity to a point of referenceUnusualChangeLot of effort on metrology. Ideas about analytical goalsAbnormality dealt with by theory of reference valuesBiological variation has a role here in that in enables utility of the approach to be identified and allows the quality standards to be set.Much of our work however is about monitoring once diagnosed therefore sinificance of change is an imperative .
5Sources of Biological Variation Biological Rhythms (time)HomeostasisAgeSexEthnicityPathologyResponse to Stimuli
6eGFR > 60 in a 30 year old white female: Changing renal function?
8Reference Values Grasbeck & Saris 1969 Introduced the term “reference value”:The mode of generation of such values is known with respect to: -Selection of subjectsAssessment of state of healthPopulation characteristics, age, sex,Specimen collection and storageAnalytical technique and performance characteristicsData handling techniques.
9IFCC Expert panel on the Theory of Reference Values The Concept of Reference Values. 1987;25:The selection of Individuals for the Production of reference values. 1987;25:Preparation of individuals and collection of specimens for the production of reference intervals. 1988;26:Control of analytical variability in the production of reference values. 1991;29:Statistical treatment of collected reference limits. 1987;25:Presentation of observed values related to reference values. 1987;25:J Clin Chem Clin Biochem
10This looks nice so far , but what is the use of biological variation data?
12Current Applications of BV Data Setting of analytical goals (CVgoal).Quality specifications for :total allowable error (TEA)Bias (BA )Evaluating the significance of change in serial results (RCV).Assessing the utility of reference intervals (Index of Individuality).Assessing number of specimens required to estimate homeostatic set points.Choice of specimen type.Timing of specimens.
13Comments on Biological Variation Data These fundamental data have many applications that under-pin our practice.We need to have confidence in the data and understand its limitations.Should we not have standards for their production and characterisation?
14Identification the nature of biological variation. What is meant by the term biological variation in the context of clinical biochemistry?A component of the variance in biochemical measurements determined by the physiology of the subjects observed.
22Quality Specifications DesirableCVA < 0.5 x CVIBA< 0.25 x (CVI2 + CVG2)0.5Tea < 1.65 x 0.5 x CVI x (CVI2 + CVG2)0.5OptimumCVA < 0.25 x CVIBA< x (CVI2 + CVG2)0.5Tea < 1.65 x 0.5 x CVI x (CVI2 + CVG2)0.5MinimumCVA < 0.75 x CVIBA< x (CVI2 + CVG2)0.5Tea < 1.65 x 0.5 x CVI x (CVI2 + CVG2)0.5
23Number of Specimens to Estimate Homeostatic Set Point n = [Z * (CVA2 + CVI2)/D] 2 D = % of closeness required
24Biological variation data simulator. WWW.biologicalvariation.com
35Observations: Creatinine Upper Reference Limits: -Male = 106 µmol/LFemale = 80 µmol/LRCV larger for men than for women.
36Implications. If True: - Clinically important as disease progression needs to be monitored and appropriate actions taken (e.g. Acute on Chronic Kidney failure).Tighter analytical performance characteristics to be applied for females.Impact will be greater on eGFR
37RCV for eGFR and Creatinine: - % Change at % ProbabilityCVI95%99%Rise in Creatinine4.310.3%14.6%5.312.6%17.8%Fall in eGFR12.8%15.4%6.816.0%22.6%Assumes a CVA = 1%
41Proposal Use eGFR for initial classification of CKD stage. Use creatinine to follow patients with RCV indicator flag?More Precise?Difficulty is that there is a suggestion that creatinine CVI is variable in disease. Therefore which CVI?
42Reported CVI for Serum Creatinine State of HealthCVINumber of SubjectsLength of Studies (days)Number Samples/SubHealthy Median?4.3CRF5.317218Type 1 DM5.92756Impaired renal function6.992116.5Post renal transplant11.54190Acute MI13.420419.5CKD children13.054540Ricos et al Ann Clin Biochem 2007;44:
43Returning question are these conclusions based on fit for purpose data?
44What are the quality standards for BV Data? What is the uncertainty? Experimental DesignData AnalysisAssay CharacteristicsWhat are the quality standards for BV Data?What is the uncertainty?
45Translated into databases 40 years of dataDo the data travel through timeMethod developmentsQualityEnough reported detail.Good Design?CommutablePopulation demographics.Healthy?Diseased?Translated into databasesExcellent ResourcesGranular enough?Data archetype required?The Literature212 references319 Constituents:90 entries based on 1 Paper
46Time ISSUES Non-complex v complex molecules. Improved assay specificity.CreatininePTH
47PTH AssaysLongish history of evolving assay systems with differing analytical performance characteristics and specificities.1970s – C-Terminal RIALate 80s – Sandwich IRMA Assay1990 – 98 Nichols IRMA assays dominateLate 1990s – variety of “intact” sandwich assays on a number of different analytical platforms.2004 – Bioactive PTH assayAdapted from M Scott Focus 2010
48Different Assays React With Different Fragments Much evidence in the literature indicating that assays react to varying extents with the variety of PTH fragments present in Serum.M Scott Focus 2010
49Impact of assay specificity If clearance of fragments is not identical in all patients and non diseased patients the apparent biological variation will vary and be assay specific.Assay specificity an important BV qualifier?
50Two studiesAnkrah Tet et al. Ann Clin Biochem 2008;45: PTH = Nichols Advantage 4 Males 6 Females “Normals” Gardham et al . Clin J Am Soc Nephrol ePress May 24th 2010 Abbot Architect Intact PTH Immunotopics Inc. Biointact PTH “Normals” 22 Haemodialysis patients
51PTH Biological Variation SubjectsnAssayPTHng/LCVICVGCVARCV (%)N-Set*“Normal”10Nichols51.725.923.85.072.32712Abbott51.919.23.554.015ImmunotopicsBio-intact 1-8427.54.267.022Dialysis303.025.63.672.026131.030.26.386.037* Number of Specimens Required to estimate homeostatic point within 10% with a probability of 95%
52Time: Length of Studies Data in chronic stable disease “often can be considered constant over time and geography”“Same order of magnitude in disease and health”
53Within Subject Variation (CVI,%) for Serum Sodium and Urea No. of Time Sex status Na+ Ureasubjectsh m H11 8 h m H62 1 d H11 2 weeks m H10 4 weeks m H14 8 weeks F Hweeks m H37 22 weeks m H274 6 months - H15 40 weeks - H9 2 d - RF15 6 weeks F HP16 8 weeks m DMFraser 2001
54Within subject Biological variation in disease: collated data and clinical consequences. Rico et al Ann Clin Biochem 2007:44:66 quantities 34 disease with 45 references.“For the majority of quantities studied CVI of same order as diseased. “Disease specific RCVs may be necessary in some cases.Effect of variability in variability not quantitatively studied.“Heterogeneity in study designs and methods compiled”
57Population description Ankrah Tet et al: I’m healthy and normal !I’m a biochemist!“Blood samples were taken at weekly intervals from 10 healthy subjects (4 men and 6 women, median age 21 years, range 19–27 years; mean body mass index 21.3, range 19.0–25.9) for six weeks at the same time of the day (between 12:30 and 14:30 h),”
58Are biological variation data fit for purpose? Need to assess on a case by case basis.Questions around uncertainty.What are the implications for their application?Can the impact of uncertainty be quantified and reduced where necessary.Accepted standard needed for their production.Critical appraisal checklist required to enable veracity of existing and new publications.Meta-analysis of dataQuestions to be addressed by the EFCC biological Variation Working group
59Production of reference values The Process: - Define the purpose for which they are to be used.Only meaningful and transferable if defined for the population or individual in terms of: -Inclusion and exclusion criteriaIntake of food & drugsPhysiological and environmental conditionsSpecimen collection criteriaPerformance characteristics of the analytical methodThe statistical methods used for estimation of the limits
60Production of reference values State of health defined.WHO Defn: -“ a state of complete physical mental and social well being and not merely the absence of disease or infirmity”Disease is a state of health.Conceptually different in different countries.The term “Reference” should be accompanied or preceded by a word qualifying the state of health. E.g diabetic, hospitalised diabetic, ambulatory diabetic, Healthy laboratory worker?
63The reference change value: a proposal to interpret laboratory reports in serial testing based on biological variation.C. RICO´ et alScand J Clin Lab Invest 2004; 64: 175 – 184“The RCV data in this study are presented as a point of departure for a widely applicable objective guide to interpret changes in serial results.”HL7 recognised conceptRequests for additional flags pending