Getting the Right Answer –the Importance of Traceability

Graham JonesMBBS, BSc, DPhil, FRCPA, FAACB

Department of Chemical PathologySt Vincent’s Hospital, Sydney

Contents

• Interpreting laboratory results• Performing measurements• The Science of Metrology• Turning Science Into Caring

Laboratory Medicine

• Our goal: To improve patient health• Our tools: Laboratory tests• Our mechanism: Support medical decisions

• To optimise medical decisions we need toproduce accurate results

• If our work aversely affects medical decisionmaking, we are not achieving our goals

Numerical laboratory results

Example:Mr Bill Bloggs (DoB 1 Jul 1950)Sample Collected: 21 Aug 2012, 10:00 am

Test Result UnitsSerum sodium: 140 mmol/L

How is this number interpreted?

Interpreting laboratory results

All results are interpreted by comparison.Comparison may be with:• A clinical decision point

• A population reference interval

• A previous result from the patient

5-Aug 1-AugSodium: 140 145 mmol/L

Professor Per-Hyltoft Peteresen, Sydney 2005

Valid comparisons

• Your results must be unbiased relative to thecomparator

• Clinical Decision Point– Method used to perform the study

• Population reference interval– Method used for the reference interval study*

• Previous result on the patient– Method used for the previous result*

*May be your laboratory or elsewhere

Adverse clinical effects - example

• LDL Cholesterol target is 2.5 mmol/L (frompatient outcome studies)

• Laboratory method has positive bias relativeto trial methods

• Patient does not get treatment

Adverse financial effects

• Unnecessary testing costs due to analyticalfactors (patient recalls, follow-up, treatment):

• Germany 1.5 Billion US$ per year– German Health Report 1998

• USA 7.5 Billion US$ per year– Willie May, Chief Analytical Chemistry NIST

• Australia? (0.5 Billion A$)

Murphy KE et al. J. Anal. At. Spectrom., 2002, 17, 469–477

Laboratory Measurements

Laboratory measurements

• All numerical laboratory measurements aremade by comparison

• Analyte concentration in the sample iscompared with concentrationin the assay calibrators.

• Done using a standard curve

• Value assignment ofcalibrators establishes assay trueness (bias)

Routine method compares patient samplewith calibrator value to give result.

Calibrator value “sets” assay trueness / bias

Value assignment of Calibrators

• Calibrators have values assigned bycomparison with manufacturer mastercalibrators

• This process uses a superior assay to fieldmethod

Each batch of calibrator needs value assignment

Done by comparison to another “calibrator”

Value assignment of Calibrators

• Master calibrator has values assigned bycomparison with …

Working calibrator has value assigned by comparison.Done by comparison to another “calibrator”

Calibration Hierarchyor

Traceability chain

Same LabSame InstrumentSame MethodSame Calibrator

Different LabSame MethodSame Calibrator

Different LabSame MethodDifferent Calibrator

Different manufacturerDifferent MethodDifferent Lab

Different Reference Lab

Different Ref material

NationalMeasurementInstitutes

Manufacturers

Laboratories

ProfessionalO

rganisations

The top of the traceability chain

• All assays are “anchored” in one of thefollowing– A Material– A Method (eg Enzymes)

Ref A Ref B

Method A Method B

Result Result

Reference Materials

• Certified Reference Materials– Produced by National Measurement Institutes– Highly purified– Purity verified (and certified)– Very accurately weighed (and certified)– Reconstituted very accurately

• May also be “Matrix matched” eg urine, serum– Values assigned by comparison with pure materials

Other Reference materials

• International conventional calibrator– Eg WHO standards

• Other suppliers– Eg US Pharmacopoeia, commercial suppliers

• Manufacturer’s In-house materials

Reference Methods

• For some analytes the a method defines thetrue result

• Examples: IFCC methods for AST, ALT, ALP• Assays NOT calibrated with pure material

• For most analytes reference methods arecalibrated by a material

• Examples: Isotope Dilution Mass Spectrometry

Who decides?

The top of the chain is vital to accuracy.What Reference Material or Method is the top

of the Traceability Chain?

Joint Committee on Traceability inLaboratory Medicine

• JCTLM - Joining of:– Metrology Community (BIPM)– Laboratory Medicine Community (IFCC)– Accreditation Community (ILAC)

• Different languages, different journals, differenttraditions, different history

• Aim to bring rigour and processes of metrology tolaboratory medicine

VIM – International Vocabulary ofMetrology

Metrology - BIPM

Bureau International de Poids et Mesures(International Bureau of Weights and Measures)

(Pont de Sevres, Paris)

Metre Convention

• The Metre Convention (1875)• Treaty to oversee the keeping of metric

standards.• In 1960, the system of units it established was

renamed the "International System of Units"(Système international d'unités or SI).

• 56 signatory countries in 2012• “..to promote world wide uniformity in units of

measurement..”

Metrology in practice

• International network of Laboratories– National Measurement Institutes

• International Treaties– Recognition of measurements

• Metrology Research– All aspects

• Legal Metrology

Measurements in general

• Ordering a machine part to fit• Selling tonnes of wheat• Knowing the time• GPS navigation

• These are all possible because of metrology!

Systeme Internationale

SI definitions

The kilogram

This international prototype, made ofplatinum-iridium, is kept at the BIPMunder conditions specified by the 1stCGPM in 1889

Achim Leistner at the AustralianCentre for Precision Optics holds

a 1-kg silicon crystal sphere.

Metrology

• In the lab – already responsible for:• Volumes, weights, light measurements,

lengths, current …• The building itself, the trucks that make

deliveries …

• Now through the JCTLM involved in assayaccuracy!

JCTLM Output

• Database of “higher Order … ”

• Reference Materials• Reference Methods• Reference Laboratories

JCTLM Review Teams

• Blood Cell Counting– Dr Mingting Peng

• Blood Groupings• Coagulation Factors• Metabolites and Substrates• Microbial Serology• Non-electrolyte Metals• Non-peptide Hormones• Vitamins and Micronutrients• Electrolytes and Blood Gases

• Drugs• Nucleic Acids• Proteins• Enzymes

Each team has volunteer scientists assessing materials and methods

Relevant ISO Standards• ISO 17511 In vitro diagnostic medical devices -

– Measurement of quantities in biological samples– Metrological traceability of values assigned to calibrators

and control materials

• ISO 18153 Metrological traceability of values forcatalytic concentration of enzymesassigned to calibrators and control materials

• ISO 15193 Reference measurement procedures• ISO 15194 Description of reference materials• ISO 15195 Reference Measurement Laboratories

Progress: 2002 - 2012

• 250 materials listed for 141 analytes• 157 methods for 80 analytes• 63 laboratory services for 32 analytes

• Still more to do!

ElectrolytesCalcium RM (P,S) RMP RMSChloride RM (P,S) RMP RMSLithium RM (P,S) RMP RMSMG RM (P,S) RMP RMSPhosphate RMPPotassium RM (P,S) RMP RMSSodium RM (P,S) RMP RMSEnzymesALT RMP RMSAST RMP RMSALP RMP RMSAmylase RMP RMSGGT RMP RMSLD RMP RMSCK RMP RMS

Metabolites and SubstratesBilirubin RM (P) RMPCholesterol RM (P,M) RMP RMSCreatinine RM (P,M) RMP RMSEthanol RM (P)5-tetrahydrofolic acid RMPGlucose RM (P,M) RMP RMSHDL-Cholesterol RMPHomocysteine RM (P,M) RMPLDL-Cholesterol RMP25-OH Vitamin D3 RM (M) RMPTriglycerides RM (M) RMP RMS(total glycerides)Urea RM (P,M) RMP RMSUrate RM (P,M) RMP RMS

Metabolites and SubstratesBilirubin RM (P) RMPCholesterol RM (P,M) RMP RMSCreatinine RM (P,M) RMP RMSEthanol RM (P)5-tetrahydrofolic acid RMPGlucose RM (P,M) RMP RMSHDL-Cholesterol RMPHomocysteine RM (P,M) RMPLDL-Cholesterol RMP25-OH Vitamin D3 RM (M) RMPTriglycerides RM (M) RMP RMS(total glycerides)Urea RM (P,M) RMP RMSUrate RM (P,M) RMP RMS

Creatinine Assays - 2013

• 43 manufacturers; 58 assays• 21 IDMS aligned* (others maybe or can be?)• Sources: IFCC survey responses; Internet

search for IFUs; personal knowledge(incomplete)

• Examples:– Calibration with aqueous calibrator may cause a

systematic error in automated procedures. Inthese cases it is recommended to use a serumcalibrator (Sentinal)

Creatinine Assays - Comments

• Many non-IDMS aligned assays available• Manufacturer’s PI / IFU often not helpful*

– Reference “NIST SRM”, not “IDMS”, not stated asassays traceable

– Some note need for Serum calibrators

• Assays in developing countries poorlyunderstood

Cystatin C

• 16 assays from 16 companies• 4 Aligned to IFCC reference material ERM

®DA471. (7 – A Grubb +3)• Dako and Abbott (only outside USA)• Roche for 2014• Options

– Advice to labs (formulae, which assays)– List of assays and formulae

Manufacturers

We want them to:• Select appropriate reference materials /

methods• Transfer values to calibrators accurately

(with minimal uncertainty)• Tell us what they are doing

– Traceability statement

Abbott

Traceability Statements

Serum Creatinine Calibrators

Traceable to SRM 967 using IDMS (both JCTLM listed)

Value within 2.5% of true value

Calibrator lots should not change >+/- 2.5%

Traceability Statements

Laboratories

• Choose methods which are:– Traceable to good references (JCTLM listed)– Have low uncertainties for calibrators– Minimise changes over time

• Select and promote unbiased comparators– Common decision points, reference intervals– “4th Pillar”

• Confirm performance with EQA, standards– “5th Pillar”

Proposal

• The AACB and RCPA should adopt thefollowing principle:

• “Laboratories should use assays traceable toJCTLM-listed materials, methods andlaboratories where possible and feasible”

• Thus: LDH LPAST and ALT with P5PGGT to IFCC not Szasz

Personal Observations…

• If labs can do it differently, they will• Unless EQA can show labs are the same, assume

they are not• If EQA shows lab differences, it will not fix itself• Action requires people talking, setting standards

and doing• Action can be local, national or international

Conclusions

• The science of metrology backs most of whatwe do– Weights, volumes, currents, lights

• Assay traceability is being added to this list• Ongoing work by metrologists, manufacturers

and laboratories is required• We are part of the traceability chain in our

labs with the choices we make: choice ofmethod/supplier, how it is run; QC;QA…

• As professional organisations we fill a vital roleallowing actions as a group.