Hello everyone and welcome back to another week of MedTech Compliance Chronicles! Over the past couple of weeks we have explored the US FDA and ISO 13485:2016 requirements related to product realization. You may have noticed that throughout all of the areas we touched on there has been a common theme around verifying your product and processes. This naturally leads to our next topic: Monitoring and Measurement. Remember, the fundamental goal of quality management is to be sure that whatever product or service reaches the customer meets all requirements associated with it. Objective evidence of this conformity must be maintained and will be the subject of audits. So, one might ask; how do you provide objective evidence that every product meets its requirements? Or you might think you know and say “well, I made all of these acceptance criteria during design and development and transfer to manufacturing and I take the measurements at the points I say I will in my procedures, isn’t that enough?” The short answer is no.
When running a medical device organization you must make sure that measurements you are taking actually reflect the true state of what is being measured. This means that the methods used must be capable and the tools must be accurate and precise. Finally, as these are some of the most sensitive and important pieces of equipment in any organization, they must be adequately protected.
Measurement System Analysis (MSA)
By this point, you have your acceptance criteria defined for everything required to produce your product. As part of that process, you should have identified and acquired the equipment necessary to perform the measurements that the acceptance criteria require. Once that is done, you will need to document evidence that the measurement system you have developed is capable of providing the information you require. The measurement system consists of the equipment used to perform the measurements, the operators taking the measurements, the objects which are to be measured, the environment in which the measurement takes place and the method of measurement chosen. All are potential sources of variation that must be quantified and reduced to acceptable levels.
MSA is the process by which you will quantify the sources of variation in your measurement system and, if necessary, take action to reduce it. This will include things like gauge repeatability and reproducibility (gauge R & R) and attribute agreement studies. The output of these studies should be compared against the acceptance criteria and a decision made as to whether the measurement system can adequately provide the information required of it. A simple example would be if you were attempting to measure a dimension with a tolerance range of 0.0035”-0.0045” with a caliper that is only sensitive to 0.005”, this caliper would not be capable of detecting the level of sensitivity you require and the output of a gauge R & R would like attribute the majority of the variation to the measurement system which would tell you mathematically that this caliper is incapable. The ultimate goal, of course, is to prove that all of your chosen equipment and methods are capable or, in mathematical terms, the variation attributable to the measurement system is acceptably low.
Calibration & Verification
MSA is quite a lot but it unfortunately only gets you half of what you need. If you think back to high school chemistry you may recall the topic of accuracy and precision. Precision is how consistent a measurement system is with its outputs. Accuracy is how close the measurement system’s outputs are to the true value. MSA provides you with the precision of your system, calibration and verification tell you how accurate your tools are.
First, you may be wondering about the difference between calibration and verification. Calibration is the process of configuring the equipment to provide results within an acceptable range in relation to the true value. Verification is roughly the same but usually much less detailed of a process and, in return, is done much more frequently. Both involve comparing the measurement results of the equipment with a known standard or reference of higher accuracy. Calibration is usually a statistical study with a lot of measurements throughout the whole range the equipment is capable of measuring and remains valid throughout a specified period of time. Verification, on the other hand, might only consist of a single measurement of a reference that is close to the desired measurement to verify that the equipment reads that range correctly but might need to be done prior to every measurement taken with that piece of equipment. In practice the decision to calibrate or verify generally depends on the type of instrument and the risk level of the attribute it measures, with calibration being favored for higher risk measurements.
There is one final point to discuss on this topic, those are the requirements around the standard or reference measurements used. For the vast majority of cases, these standards need to be traceable to international or national standards. This means that whatever is used as the “true value” measurement but be traceable back to a recognized true value for that unit. In addition to that, the accuracy of the standard you use, compared to the recognized true value, must be greater than the accuracy of the measurement you are trying to obtain. For example, if you need to measure something at 0.001”, the standard used to calibrate or verify the tool must be accurate to at least 0.0005”. When a recognized standard does not exist, you must document the means of verification. This is another case when verification would be chosen over calibration. In practice, this would be chosen for things like layovers or optical comparators or anything that is specific to your organization and not utilized externally. To provide evidence of the accuracy you may document the machining of such a standard with high precision machining, followed by a detailed inspection with calibrated instruments.
Protection & Identification
The final two requirements around monitoring and measurement equipment is that they be identified and protected from any damage or conditions which would invalidate their results. Remember that this equipment is what you are basing all of your judgements as to whether or not your product conforms to its requirements on. In addition to that, a lot of measuring equipment is, by nature, quite sensitive. Ensuring that measuring equipment is properly handled, stored and taken care of is paramount to maintain the validity of your measurement system. You should train all operators who use such equipment on how to handle it and know when it has been mishandled.
There are a couple additional requirements around the identification of measuring equipment to the general requirements for equipment that we have discussed prior. Namely, these include the date of the last calibration and the due date for the next calibration. The operator who performed the calibration must also be identified.
Conclusion
This post should have provided an explanation of the requirements around monitoring and measurement. The requirements really are just focused on how you know that the tools and methods you have chosen to measure your product are giving good results and if they are even able to give you the results you need at all. Unfortunately, this post is just the beginning to being able to implement a robust monitoring and measurement system, just touching on the requirements and hinting at how to meet them. Performing much of these tasks are entire other topics on their own and likely will be the topics of future posts.
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