Customer Misuse – What it is and what to do about it

The Issue

A manufacturer designs a diagnostic assay system and after considerable testing, the assay is approved by regulators and sold. Subsequently, there are some patient harm incidents traced back to incorrect results from this assay. Upon analysis, the manufacturer maintains that the incorrect results were caused by customer misuse.

The spectrum of customer misuse

When I worked for a diagnostic company, I remember a product that had poor reliability. In meetings devoted to solving the reliability issues, the head of engineering claimed for many of the problems that he could do nothing, because the problem was caused by customer misuse. One of these problems stuck in my mind because the customer was required on a regular frequency to disassemble a valve and clean it. To frequently rebuild the valve seemed excessive and the next generation product employed a new design which obviated this maintenance.

An example on another end of the spectrum is that some instrument systems allow the user to delay a required calibration. If the user continues to delay the calibration and to either not run quality control or to ignore failed quality control, incorrect results could easily be generated.

Although in the second case, one could argue that the user had violated the policy set up by the laboratory, the same might be true for the first case.

Of course there will be customer misuse issues which are less black and white (if in fact the above examples are).

These are hypothetical examples. A real example was reported for a home glucose analyzer (1) when users did not completely insert the reagent strip and got incorrect results leading to some hospitalizations. Not completely inserting the strip did not cause any error message and also represented an example of not following the instructions (e.g., customer misuse). In this case, the government successfully brought legal action against the manufacturer. In another example, a clinical laboratory (Maryland General Hospital) grossly violated their own policies (2).

Regarding customer misuse and blame, the taxonomy for errors described by Marx (3) is of interest.

The FMEA (fault tree) approach to customer misuse

If one sets up a FMEA or fault tree, the effect “incorrect results” can be caused by a variety of events, and the cause of these events can be the customer doing something incorrectly (customer misuse). Actually, some companies divide FMEAS into separate categories, with one FMEA devoted to customer use (e.g., misuse).

There are several questions to be addressed in these customer use FMEAs (as with all FMEAs).

  • what is the severity of the event caused by misuse– e.g., will it lead to potential patient harm such as potential causing incorrect results
  • what is the estimated probability of occurrence
  • what is the best control or mitigation to prevent this misuse error from occurring
  • what is the best way to detect this misuse error and recover from it

The spectrum of solutions for preventing customer misuse

Just as there is a spectrum of customer misuse, there is a spectrum for the mitigations to prevent customer misuse. The default mitigation for customer misuse is virtually always customer training ranging from the instruction manual (and offshoots such as videos) to onsite training. One must understand that since there is always an instruction manual (or package insert), the mitigation is to improve the instruction manual. The mechanism to do this involves usability testing. The other end of the spectrum is redesign. As the reliability consultant Ralph Evans suggested “make it easy to do the right thing and hard to do the wrong thing.” A previous essay on a medical error also illustrates this spectrum.

Some of the mitigations are also not that black and white. Consider a manufacturer that has conducted extensive interference testing for an assay and has reported in the product insert that 7 drugs interfere with the assay and when any of these substances are present above the concentrations listed, the manufacturer’s assay should not be used. If the clinical laboratory is wired into the hospital’s EMR (Electronic Medical Record) assuming that an EMR exists, one could suggest that rules could be built into the LIS (Laboratory Information System) to follow the manufacturer’s recommendation. Without these computerized systems, one would have to manually inspect (potentially) each patient’s medical record, which is a daunting task.

The current environment

Ever since the Auto Analyzer was invented, the trend has been towards instruments that are easier to use. Since clinical laboratory staff are less trained today, manufacturers design their products to be easier to use to gain competitive advantage and advertise this feature. Regulators such as the FDA also recognize the value of ease of use and require hazard analysis.

Ease of use is thus a key product attribute for many systems and fulfills Ralph Evans suggestion. But there will nevertheless always be customer misuse issues and each one must be considered with the result that some will be shown to be the responsibility of the manufacturer, some the responsibility of the clinical laboratory and for some agreement of responsibility will never be reached.


  1. Assay Development and Evaluation: A Manufacturer’s Perspective. Jan S. Krouwer, AACC Press, Washington DC, 2002, pp 1-3.
  2. See:
  3. Marx, D. Patient Safety and the “Just Culture”: A Primer for Health Care Executives

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