Evidence Based HbA1c Accuracy. Sabrina Koetsier Medical Scientist RCPAQAP Chemical Pathology

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1 Evidence Based HbA1c Accuracy Sabrina Koetsier Medical Scientist RCPAQAP Chemical Pathology

2 Fresh lycohaemoglobin This program is designed to assist laboratories to assess the accuracy of their hihba1c method Specifically the program allows valid assessment (A) between different methods, (B) by comparison with a reference method and (C) investigation of abnormal Haemoglobin variants Current lycohaemoglobin Program uses a lyophilised haemolysate which exhibits matrix effects especially for immunoassay methods The Lyophilised material provides more samples for valid statistical analysis to assess imprecision

3 Fresh lycohaemoglobin cont d The fresh whole bloodhba1c program will not replace the lyophilized lycohaemoglobin Program Samples collected from patients in collaboration with the AACB Working Party Members Send around the world Human samples, close to clinically relevant values. Six samples per year, two in March, June and November

4 Target Setting SKML European Reference Laboratoryfor lycohaemoglobin Member of IFCC HbA1c network Values have been assigned in triplicate with two IFCC Secondary Reference Measurement Procedures, IFCC calibrated. NSP values are derived from the IFCC values using the master equation.

5 eneral Performance Participants p are able to report in both units We encourage participants to report the unit they use for reporting patients In Australia should be reporting both units S l %(62 l/ l) Sample 1 03, 7.8% (62 mmol/mol) Number of outliers: 3

6 Participation Num mber of participa ants NSP IFCC Whole Blood

7 Sample 1-03 July ALP High = 8.3 % NSP (%) Target/ Median = 7.8 % ALP Low = 73% 7.3%

8 Factors that can influence HbA1c Iron Deficiency Anaemia Aspirin i Renal failure Are laboratories/physicians taking these into account when reviewing i results? Lipid disorders Pregnancy Are patients at risk of being misdiagnosed with diabetes in the Alcohol future? Hb variants eg HbF, HbC, HbS Other

9 It s all in the Variant There are over 600 variants The Hb variants worldwide in descending order are: HbF, HbS, HbE, HbC and HbD... Patients that are heterozygous for any of these Hb variants are usually asymptomatic and have normal red cell survival A physician may be unaware that their patient with diabetes has one of A physician may be unaware that their patient with diabetes has one of these variants

10 To Diagnose or not to Diagnose? HbA1C should be able to be used to diagnose diabetes as long as the Hb variant does not interfere with the assay type nor affect red cell survival For example: the presence of some variants can affect the net charge of the haemoglobin and result in false HbA1C values. 11

11 Method Interference from Interference from Interference Interference Interference from HbC HbS from HbE from HbD elevated HbF Abbott Architect/Aeroset $ Arkray ADAMS A1c HA 8180V (Menarini) No No HbA1c not quantified HbA1c not quantified No Axis Shield Afinion No No No No $ Bayer A1cNOW Yes Yes No No $ Beckman AU system Yes Yes No No $ Beckman Synchron System No No No No $ Bio Rad D 10 (A1c program) No No No No Yes >10% HbF Bio Rad Variant II NU No No Yes >10% HbF Bio Rad Variant II Turbo No No Yes Yes Yes >5% HbF Bio Rad Variant II Turbo 2.0 No No No/Yes (conflicting) No Yes >25% HbF Bio Rad in2it Yes No Yes No $ Ortho Clinical Vitros No No No No $ Roche Cobas Integra en.2 No No No No $ Roche/Hitachi (Tina Quant II) No No No No $ Sebia Capillarys 2 Flex Piercing No No No No Siemens Advia HbA1c (original ) $ Siemens Advia A1c (new version) $ Siemens DCA 2000 No No No No Yes >10% Siemens Dimension No No No No $ Tosoh 7 Yes No Yes No No Tosoh 8 No No Yes No No Trinity (Primus) HPLC (affinity) No No No No Yes >15% HbF

12 Analytical Principle Immunoassay Antibodies recognize the structure of the N terminal glycated amino acids of the Hbβ chain N Terminal lucose Val His Leu Thr Pro lu Enzymatic (new method) Antibody binding Uses an enzyme that specifically cleaves the N terminal valine N Terminal lucose Val His Leu Thr Pro lu Enzyme cleavage

13 Analytical Principles Cont d + Boronate affinity M aminophenylboronicacid i id reacts specifically with the cis diol groups of glucose bound to Hb. Measures total glycated haemoglobin First peak + + Second peak + Ion exchange HPLC Separates based on charge differences between HbA1C and other haemoglobins

14 Send out 1-06 November 2012 Sample 1 06 Target 8.1% (66 mmol/mol) Number of outliers: 10 Contained 5.5%HbF

15 Sample 1-06 December 2012 HbA A1c NSP % ALP High = 8.6 % Target = 8.1 % Median = 8.0 % ALP Low = 7.6 % 7

16 IFCC results versus Analytical Principle HbA1C (mm mol/mol) Variants have been 1 05 analysed and found not to affect the Afinion TM HbA1c test result. Most immunoassay s state: No interference with HbF <10% HbA1C (mm mol/mol) Target Manual Affinity Automated Affinity HPLC Immunoassay 56 Target Manual Affinity Automated Affinity HPLC Immunoassay Whyisthere a noticeable difference?

17 What do we measure? IFCC reference methods (LCMS) = HbA1c/(HbA1c + Hb0) Ion Exchange HPLC = HbA1c area/σhba area [HbA1c] = change in scatter between Hb0 and HbA1c

18 What do we measure? Immunoassay = [HbA1c]/[Total Hb] Decrease in scatter quantified using a calibration curve of absorbance. Boronate affinity = Total Hb/Total Hb The analyser evaluates the precipitate on the membrane by measuring the reflectance. The ratio between them (glycated haemoglobin and total haemoglobin) being proportional to the percentage of HbA1c in the sample. High Scatter Low Scatter

19 68 Possible Cause? 1 06 Immunoassay = [HbA1c]/[Total Hb] Boronate affinity = Total Hb/Total Hb 66 HbA1C (m mmol/mol) Target Manual Affinity Automated Affinity HPLC Immunoassay MeasuringHbA1cdepends asmuchon the Haemoglobin level as the HbA1c level Boronate Affinity?Folding of the chain Less available binding sites

20 What is HbA1c? HbA1c is currently defined as: Hemoglobin A which h is irreversibly ibl glycated at one or both thn terminal lvli Valines of the chains in the tetramer. lycation elsewhere on the or chains is irrelevant. N N N N N All of these are HbA1c

21 What is Hb lycohaemoglobin, or Hb, or Total Hb, is defined as: Hb having one or more sugars irreversibly attached at any point in any of the globin chains This also includes all forms of HbA1c N N N N All of these are Hb (but not HbA1c)

22 HbF versus it s mates Simplified display HbF does not have Valine terminal This is why HbS, HbD... result in a similar fashion on lucose lucose lucose Val Val His His His Leu Leu Leu Thr HbF Thr HbS Thr Pro Pro Pro lu lu lu immunoassay HbD

23 Total Hb Introducing an error? This only includes the β subunits and is not equivalent to the HbA concentration. When there is 5% HbF you could be introducing a 5% bias. With increased HbF concentration there will be an increased bias.

24 Are you spotting the variant? Haemoglobinopathies are the commonest genetic defect df worldwide with ihan estimated 269 million carriers. Certain populations are particularly at risk of having a haemoglobinopathy, for example, in South East Asia, there are 90 million carriers, about t85 million in sub Saharan Sh Africa and 48 million in the West tpacific region Clin Biochem Rev February; 27(1): PMCID: Diagnosis of the Haemoglobinopathies Ronald J A Trent Many variants are not affected Our choice of method dis important

25 Utilising the EQA We should have methods which are either: Resistant to the effect of a haemoglobinopathy Where the haemoglobinopathy can be identified with an alternate method For Hb D,E,C,S this should always be the case Can be educating about your method Use the EQA when selecting a method or validating your performance Does your laboratory have measures in place to detect and action?