Alternatives to Six Sigma

March 19, 2008


This entry continues where the entry (Six Sigma can be dangerous to your health) left off. Given the problems with six sigma, what are some solutions to estimate the quality of an assay, using hCG as an example assay.

First, when total analytical error is calculated to estimate the values in zones A-C in an error grid, one should use conservative methods such as the empirical distributions suggested by the CLSI EP21A method, and where no data are deleted. Let’s say a clinical laboratory has done this evaluation with 40 patient samples for a new and reference method and found no results in zone C for an hCG assay. What can one conclude? Although there are 0% of the values in zone C, the 95% confidence interval extends to 7.2%. This means that for every million hCG results performed, up to 72,000 results could be in zone C. This is not very comforting and these types of evaluations don’t prove much, although one knows that the 7.2% rate is unlikely (because if this rate to occurred, it would be noticed).

FMEA is an approach that will provide an answer to the quality question but in its complete form, it requires considerable effort. To complete a FMEA analysis, one has to postulate all possible reasons why a result could fall into zone C. To get an idea of what is involved, take two possible failure modes, HAMA interference and a patient sample mix-up.

HAMA interference – To estimate the likelihood of a zone C result from HAMA interference, one needs to know the level of HAMA that will cause erroneous results in the assay and the probability of such levels in the population being sampled. Contacting the manufacturer might give one the level of HAMA to watch out for – I am not familiar with data about the distribution of HAMA in patient samples. Yet, one knows HAMA interference occurs (Clinical Chemistry. 2001;47:1332-1333).

Patient sample mix-up – There are some data for patient sample mix-ups (Archives of Pathology and Laboratory Medicine: Vol. 130, No. 11, pp. 1662–1668). However, it seems that these cases are caught within the laboratory. One would need to determine how many cases actually are not caught within the laboratory. One could then model the likelihood of a zone C result by sampling from the empirical distribution of hCG results that are observed on the lab to see the likelihood of a mix-up causing a zone C result.

Because there are so many existing data in a clinical laboratory, one may also have the opportunity to perform FRACAS types of analyses. That is, in addition to modeling probabilities, once could use existing data to count actual failures.

One must then continue:

  • with each other possible failure mode, calculate the probability of zone C results
  • calculate the overall probability of zone C results (from all failure modes) and determine if that risk is acceptable
    • special software is typically used to perform these calculations
  • construct a Pareto table if the overall probability of zone C results is too high and
  • propose control measures to lower the overall risk to an acceptable level
    • the control measures must of course be affordable

At this point, one can get the idea that this level of effort is out of reach for clinical laboratories since the level of expertise and work need just to estimate the likelihood of a zone C result is huge. Even if a clinical laboratory could perform this task, it makes no sense to require every clinical laboratory to do so.

One possibility is to have a standards group tackle such a task., although this too has limitations as was shown for a (universal) control measure to prevent wrong site surgery.

Another possibility is to perhaps leverage resources beyond the clinical laboratory. For example, one could insist that before treatment for trophoblastic carcinoma, an hCG result should be confirmed either by performing a reference assay or perhaps by treating the sample and rerunning it. This requires an interaction between the clinical laboratory and clinicians.

So there are no easy answers to preventing severe, low frequency failures, (that cause patient harm) but as discussed before, coming up with a sigma estimate for an hCG assay, is also not the answer. Nor is doing nothing.

Jan gets an award

March 15, 2008

I recently spoke at the Quality in the Spotlight conference in Antwerp, Belgium and gratefully acknowledge being awarded the Westgard Quality Award. This award was presented by Jim Westgard himself. The Quality in the Spotlight conference is a two day conference in Antwerp, devoted each year to a quality theme. This year’s theme was quality tools. I spoke about FMEA on each of the two days. It wasn’t until the second day of the conference that I realized that some of the other presentations were bothering me – perhaps I had a case of brain jetlag. This is an interactive conference so had I been quicker I would have presented my concerns to the speakers. But this did not happen so my concerns are in the previous entry to this blog. Prof. Dr. Jean-Claude Libeer, who founded the conference and also spoke about me with respect to the award, said that it was my blog which impressed people. So perhaps my previous entry could be taken as an acceptance speech.

On the second day, per instructions, I attempted to do a “workshop”. This is in quotes because I had to involve the audience but was only given one hour. Had I to do this again, I would have given an award to one lady, who answered some of the questions I posed to the audience. One example – name a case of at risk behavior that you have experienced. Answer, a technician, who had trouble getting a barcode on a patient sample to register, scanned the barcode from another patient. So perhaps this is also an illustration of the need to perform a FMEA on a control measure (what can go wrong with implementing barcodes).

Another highlight of my trip was spending three days in Amsterdam and hearing that in spite of frequent mistakes, my Dutch is begrijpelijk (understandable).

Six Sigma can be dangerous to your health

March 13, 2008

This blog entry has now been published, here.

At risk behavior

March 3, 2008

I am involved in risk management standards for clinical laboratories, where the focus has been on understanding how manufacturer’s devices can fail and how a clinical laboratory can put in place control measures to prevent these failures from causing harm.

My concern with these standards is that there is not enough emphasis given to the clinical laboratories own sources of error – its people. Among problems related to human errors are cognitive errors, non cognitive errors, reckless behavior, and at risk behavior – the topic of this entry.

At risk behavior is behavior that increases risk where risk is not recognized, or is mistakenly believed to be justified. Anyone who manages people must have had the experience by hearing  (perhaps second hand) “I don’t think that’s necessary and I’m not going to do it.” And of course, parents are familiar with at risk behavior practiced by their children.

An example of healthcare at risk behavior is reusing syringes. This occurred recently at an endoscopy clinic in Nevada and has affected up to 40,000 people. In reading the patient empowerment blog, one learns about other cases of reused syringes. In a case in Long Island, the physician reused syringes only for the same patient, but the syringes were used with multi-dose vials and these vials were used across patients.

In the recent case of reducing central line infections, Dr. Peter Pronovost observed that of the steps associating with placing a central line, in a third of patients, doctors skipped at least one step. Whereas, some of this could be attributed to non cognitive errors (slips), it could also be associated with at risk behavior. The control measure that worked here, was a double check step, whereby another healthcare provider would check to make sure each step was followed.

Discovering at risk behavior may not be easy, hence it needs to be on one radar’s screen.