Recommended reading – CAP interview of Jim Westgard regarding lab QC over the last 30 years including the current focus on risk management: http://www.captodayonline.com/lab-qc-much-room-improvement/
This is the full paper http://dst.sagepub.com/content/early/2014/10/10/1932296814554415.abstract – a Letter to the Editor was already mentioned.
The paper suggests that a different glucose error grid is needed for diabetes complications such as diabetic retinopathy rather than the traditional glucose error grid which deals with acute injuries. This is because slightly or even moderately elevated glucose would fall in the no treatment needed zone of a traditional glucose error grid but would be harmful for diabetic complications. Thus, a glucose meter could look good in terms of a traditional glucose error grid but have a bias that would allow elevated glucose to occur for up to 6 months – until the patient’s next A1c determination. Patients and providers would be better informed if they knew which glucose meters were free from these long-term biases.
This entry adds to but does not contradict the Westgard Web site’s: http://www.westgard.com/badqc-goodsoftware.htm
Clinical limits provide a range of results that do not cause patient harm.
A problem with traditional clinical limits is that going from just under the limit to just over the limit changes the outcome from no harm to harm. This is difficult to understand for two results that are almost identical. That is why error grids were developed. They separate harm into categories so when one goes from just under the limit to just over the limit the outcome changes from no harm to minor harm.
QC limits are set to control the process
Thus, QC and clinical limits are different.
For an assay with a high process capability (similar to a high six sigma) clinical limits will always be much wider than QC limits. And for an assay that is out of control (values that exceed QC limits), results may still be within clinical limits. But it is nevertheless important to detect an out of control process because the process may become so out of control so that results fail clinical limits.
For a process that is in control (all values that within QC limits), can results be outside of clinical limits (potentially cause patient harm?) YES!
Patient spills coke on himself. Provider comes in to use glucose meter and fails to wash and dry the site from which the capillary sample is taken. The result is 200 mg/dL too high. There is nothing wrong with the glucose meter or QC.
Patient has an interference. Result is way off. QC is ok.
There is a one hour shift in results – they are way off. QC – once every eight hours doesn’t detect the shift.
Thus, QC detects long-term bias which is important but there can still be other errors that can harm patients.
Looking at the table of contents of Clinical Chemistry for September, there is a list of the most downloaded point / counterpoint articles and I am number one on this list for my discussion of GUM (The guide to the expression of uncertainty in measurement): http://www.clinchem.org/content/60/9/1245.full
For those who have had some papers rejected over the years (like me), this post is worth reading … http://majesticforest.wordpress.com/2014/08/15/papers-that-triumphed-over-their-rejections/
There was a symposium about glucose meters with three outstanding talks. BTW, one nice feature of this year’s AACC meeting was that one could easily download each speaker’s presentation. The first talk by Dr. David Sacks reviewed the current glucose meter error grids:
the 2013 version of ISO 15197 for SMBG meters
the 2013 version of POCT12-A3 for hospital meters
the 2014 draft FDA guidance for SMBG meters
the 2014 draft FDA guidance for hospital meters
Dr. Sacks never mentioned that the 2014 draft FDA guidance for hospital meters says: don’t use the ISO standard – it does not adequately protect patients. Now, the FDA probably meant don’t use POCT12-A3, since that standard is for hospital meters, but the point is FDA is not happy with either the ISO or CLSI glucose meter standard, which is why they wrote their own.
After the talks, there was a question and answer session whereby Mitch Scott, the chair of the symposium, asked Dr. Sacks why the POCT12-A3 standard allows 2% of results to be unspecified (meters can have any values relative to reference). This is somewhat of a strange question since Dr. Scott was a member of the POCT12-A3 committee and previously answered this question himself in a public meeting – as the 2% was a compromise. Dr. Sacks’s answer was different. He said you can’t prove that 100% of the results are within limits, which is of course true but this is not a reason for setting such a goal. I made this point in a brief comment. I have also published the absurdity that goes with Dr. Sacks’s reasoning in that no one would specify a goal for 98% “right” site surgery (95% in the article since it dealt with an earlier standard) – see: Wrong thinking about glucose standards. Krouwer JS Clin Chem 2010;56:874-875. And since there are about 8 billion glucose meter results in the US each year, allowing 2% to be anywhere means that 160 million glucose results could potentially harm patients. Another way to say that 2% of a huge number is still a very big number.
This is a Letter to the editor (1) based on a new revision to the glucose meter error grid (2). The gist of the Letter is as follows. The glucose meter error grid procedure involved surveying clinicians as to what glucose levels would prompt them to treat patients. But this deals with symptoms or acute injury. If a glucose meter met these limits, one might think all is well. But diabetes also involves complications from continued elevated glucose. The Letter proposed a different error grid is required for chronic injury.
- Krouwer JS and Cembrowski GS Acute Versus Chronic Injury in Error Grids J Diabetes Sci Technol. http://dst.sagepub.com/content/early/2014/07/16/1932296814543662 Note: subscription may be required.
- Klonoff DC, Lias C, Vigersky R, et al The surveillance error grid. J Diabetes Sci Technol. 2014;8:658-672.