NGSP News Archive: Summer 2009 Meetings

Clinical Advisory Committee | NGSP Steering Committee | Manufacturer Forum

2009 NGSP/IFCC Manufacturer Forum

American Association for Clinical Chemistry, July 2009

David Sacks —Chair, NGSP Steering Committee
Randie Little—NGSP Network Coordinator
Cas Weykamp—IFCC Working Group Network Coordinator
Michael Steffes—NGSP Steering Committee

Present were members of the NGSP Steering Committee and representatives from various manufacturers, laboratories and agencies.

1.       NGSP Progress Report—Randie Little, NGSP Network Coordinator

  • Status of HbA1c measurement
    • The numbers of certified methods and laboratories continues to increase.
    • We now have a number of certified labs worldwide including laboratories in China, Australia, South Africa and South America.
    • There has been much improvement in the comparability of HbA1c results since 1993.
  • CAP GH2 survey 2009A:
    • Looking at the mean ±2SD vs. the NGSP target, results for many individual methods fall mostly or entirely within ±6% of the NGSP targets.
    • All of the method-specific means were within 0.3, 0.4 and 0.5% HbA1c of the NGSP targets at the low, middle and high HbA1c levels, respectively.  19/27 methods showed mean biases of <0.3% HbA1c at all three levels.
    • Method-specific, between-laboratory CVs ranged from 1.2 to 8.0%.
    • However, approximately 95% of labs were using methods that had CVs <5.0% at all three levels.
    • The all-method CVs have shown a downward trend since 2000, especially in the normal range, and are currently ~4.5%.
  • Efforts to reduce variability
    • Tightening of NGSP certification criteria
      1. Starting January 2010 the NGSP will tighten the certification criteria for the 95% CI of the differences between a manufacturer method and the NGSP from ±0.85% to ±0.75% HbA1c.
      2. The criteria for Level 1 Laboratories will be tightened from ±0.75% HbA1c to ±0.70% HbA1c
    • Tightening of CAP Criteria (DS will discuss).
  • Influence from Hb variants
    • With HPLC methods interference from Hb variants can generally be detected in the chromatogram, we are more concerned about immunoassays that show interferences as there is no indication of an interference.
    • Several immunoassay methods that show interference are being replaced by newer methods that do not have interference.
    • 6.5% of laboratories are using methods with clinically significant HbAS and /or HbAC interference.
    • At least 20% of laboratories are using methods with clinically significant HbAE interference, and at least 6% of laboratories are using methods with clinically significant HbAD interference.
    • Once the original Roche Integra method is phased out only 5% of labs will be using methods with clinically significant HbAS and/or HbAC interference.
    • The NGSP will continue to investigate new methods for potential interferences from hemoglobin variants.

2.       CAP Grading, future plans—David Sacks, Chair,  NGSP Steering Committee

  • In 2007 CAP began using accuracy grading with acceptable limits of ±15% of the NGSP target.  This resulted in a 99% pass rate.  In 2008 the acceptable limit was reduced to ±12% and in 2009 to ±10%.
  • The limit will be further reduced to ±8% and ±6% in 2010 and 2011, respectively.
  • For the GH2 2009A survey the overall pass rates at the three levels of 5.1%, 6.0% and 8.4% HbA1c were 95.2%, 96.6% and 97.1%, respectively using the current limit of ±10%.  Using the projected 2011 limit of ±6%, the respective pass rates would be 92.1%, 90.5% and 92.9%.
  • Each lab was told in their report whether they would have passed at the future ±6% limit.
  • Looking at individual methods most showed high pass rates (>90%) with the current ±10%.
  • Using a limit of ±6% many methods still show pass rates >90%, some even show pass rates of 100%.
  • The CAP surveys clearly indicate overall improvements in the performance of assays.

Discussion: Many widely-used POC methods are CLIA-waived and therefore are not well-represented on the CAP survey since users are not required to participate.  This is an issue of great concern, as we have no way of knowing how many labs are using these methods or how well they are performing in the field.  The recent Expert Committee report recommending that HbA1c be used for diagnosis specifically excluded the use of POC methods for this purpose.  There is currently no CLIA precision specification for HbA1c as is the case for many other analytes.  The NGSP assigns target values for CAP samples using all of the network SRLs (currently 7), each SRL analyzes each sample in triplicate over two days.  The uncertainty is very small, the NGSP will calculate this and provide this to manufacturers.  When the CAP criteria are lowered to ±6% in 2011, this only allows for an error of ±0.3% HbA1c in the normal range, and some of this is taken up by the uncertainty of the IFCC network, NGSP target value assignments for the CAP samples, etc.  Also, with allowable error this small, random outliers may be a major challenge.  There are a few methods that show pass rates under 80% with the ±6% criteria, but these are used by few laboratories and will likely be phased out.  CAP will try to make the highest HbA1c level ~10% in future surveys.

3.       IFCC Network Update—Cas Weykamp, IFCC Network Coordinator

  • The IFCC Network is the global anchor for HbA1c standardization.
  • The IFCC Network has systems in place to assure continuity and quality, and provides services to manufacturers, EQAS organizers and others.
  • There was a problem with the 2008 batch of IFCC primary calibrators, these were not approved and will not be used by the network.  This will not affect the IFCC reference method; there are enough previous approved lots to last four years.
  • Master Equations: Relationships between the IFCC network and DCM networks
    • The IFCC/NGSP relationship has remained stable at all HbA1c levels, the relationship between the IFCC and Swedish system has also remained stable.
    • The relationship between the IFCC and Japan (JDS) system has shown a trend at high HbA1c levels.
  • Last year the IFCC progress report was published in Clinical Chemistry.
  • Tools provided to manufacturers to achieve traceability
    • Calibrators with both IFCC (mmol/mol) and NGSP (%) numbers as well as HbA1c and total Hb in mmol/L and g/dL, with expanded uncertainties.
    • Three levels of controls with expanded uncertainties.
    • Monitoring program to monitor traceability
      • 24 samples/year
      • Results for a given manufacturer are known only to them.
      • Traceability certificates are provided to manufacturers upon request.
  • Which units are to be reported?
    • The ADA/EASD/IDF/IFCC consensus statement called for reporting results in both IFCC and NGSP units, and if the ADAG study showed it was feasible, estimated average glucose (eAG) would be reported as well.
    • Implementation of the consensus statement has proven to be problematic, different countries have decided to report different units.
      • Germany will report only IFCC units.
      • The UK has decided to report NGSP and IFCC units for two years, after which only IFCC units will be reported.  eAG will not be reported.
      • Several other countries are following the UK approach.
      • Japan will report IFCC and JDS units.
      • The U.S. will report eAG and NGSP.

Discussion: Politics has resulted in different countries deciding to report different units, but at least we now have equations that allow easy conversion between the different units.  Values for the calibrators of the IFCC Network are set using the mean of all of the network laboratories (currently 12).  This means that the uncertainty is low and it is specified, it translates to approximately 0.1% HbA1c in NGSP units.  When using 8 levels of calibrators the uncertainty of the calibration curve will be less than 0.1% because each level has this uncertainty, therefore some will be high while others will be low.

4.       Global Standardization and use of eAG—David Sacks

  • The 2007 ADA/EASD/IDF/IFCC stated that HbA1c results were to be reported in IFCC units (mmol/mol), NGSP units (%) and if the HbA1c-derived average glucose (ADAG) study fulfilled its a-priori criteria ADAG was also to be reported.
  • The ADAG study fulfilled the a priori criteria, the final equation was:
    1. eAG mg/dL = 28.7 x HbA1c – 46.7
    2. eAG mmol/L = 1.59 x HbA1c – 2.59
  • The reporting of eAG has proven to be controversial, a number of countries have decided not to report it.
  • The American Diabetes Association feels that reporting eAG is very important and has launched an educational campaign.
  • The AACC position on eAG was published in January 2009 and recommended that laboratories in the US report eAG along with HbA1c
  • Current status of Reporting eAG
    • Several laboratories in USA have been reporting eAG with HbA1c for some time
    • 1 in 6 of all laboratories participating in CAP surveys report eAG
    • This fraction is likely to increase.
    • Many laboratories using wrong equation to calculate eAG

5.       HbA1c for Diabetes Diagnosis—Michael Steffes, NGSP Steering Committee

  • I could not have made the case for using HbA1c for diabetes diagnosis without the efforts of the manufacturers to improve the precision and accuracy of HbA1c assays.
  • The CAP adopting accuracy grading for HbA1c testing with NGSP targets and the tightening of their criteria for acceptable performance were very important in making the case for the use of HbA1c for diagnosis.
  • The International Expert Committee considered the advantages of HbA1c vs. glucose and in the end decided to recommend HbA1c for diagnosis.
    • Data from several studies clearly show an increase in retinopathy at HbA1c levels above 6.5%
    • Pre-analytical issues are a vexing problem for glucose but are not an issue with HbA1c.
    • Intra-patient variability of HbA1c is much smaller than for glucose.
    • In terms of macrovascular disease, recent studies show increasing risk of cardiovascular disease with increasing HbA1c levels over 5.5%, in people with and without diabetes.
  • The issue of pre-diabetes has proven to be more contentious.
    • With glucose there are the pre-diabetes categories of IFG and IGT.
    • The committee recommended that individuals with HbA1c levels ≥ 6.0% but less than 6.5% receive preventative intervention while at the same time recognizing that the relationship between HbA1c and risk is a continuum.
  • There has been resistance to the recommendation from some in Europe and even in the U.S. that are reluctant to get away from glucose for diagnosis.
  • WHO
    • WHO has to think globally and there are cost considerations, particularly in developing countries.
    • WHO will likely recommend that individual countries can use HbA1c for diagnosis if they wish to do so; otherwise the use of glucose is also fine.
  • Cardiologists are very much aware of glycemia as a risk factor for macrovascular disease; more studies will be coming out showing the relationship between HbA1c and CVD even in individuals without diabetes.

Discussion: There could be risks if people with diabetes aggressively push HbA1c levels downward into the normal range.  There are data from clinical trials showing that for people without diabetes, interventions that lower HbA1c lower the risk for developing diabetes.  It is likely that the ADA will endorse the recommendations of the Expert Committee by the end of the year.