Blog: Applications
Testing the Limits in LIMS - Part 2
15th March 2022
In part 1 we discussed what limits are and the types of limits found in laboratory testing, including specification, test, instrument, and analytical limits. In part 2 we shall discuss how these limits are applied to a LIMS.
Applying Limits within a LIMS
A LIMS needs to have built-in flexibility to easily apply different types of limits within the broad range of industries served. Matrix Gemini LIMS (Matrix), from Autoscribe Informatics, is well known for its highly flexible capabilities and, naturally, can handle all these limit types with ease.
Test limits (covering testing limitations of the test) are entered against the test itself. A test matrix covering the test results that need to be captured, once defined, can be used many times without being changed. Defining test limits at this level ensures the testing boundaries are set up and applied consistently every time the test is used.
Instrument/Analytical limits may be defined at the test level if they are applicable under all circumstances where the test is used. However, they may need to be defined at other levels if they are dependent on the method used or substance, product or sample type being tested.
Specification (or product) limits are applied at the product or substance level. In Matrix multiple different tests may be associated with a single product or substance. Limits may be applied to each test making the test limit unique to that product or substance. In this way substance A may have different limits to substance B, even though the underlying tests are, in effect, identical. In a similar way, limits on a product for supermarket X may be specified differently to the limit on the same product for supermarket Y. Substance limits are applied independently to, but together with, the test limits and therefore can be used to define tighter limits related for an individual substance. For example, the test limits might be set to trap errors such as a pH greater than 14, but the substance specification limits might be set to between 6.5 and 7.25 and be specific for the particular substance or product under test. The entered value for the result will be evaluated against both limits.
Sample limits are applied for each unique sample during sample registration, if needed. This allows specific or ad-hoc limits to be applied to individual samples. It is a perfect way to capture the ad-hoc/one-off specification limits required during research and development trials for instance and is just another example of the need for flexibility.
Finally, stability limits are associated with the required tests at the time that the stability protocol is defined. This means that there is an option for the limits to be held constant throughout the study even if the product limits change during this time.
Blog: Applications
Limit Actions
When a limit is breached, different actions can occur depending on how the limits have been set up. These include:
In addition to the above a special Apply Limit exists that allows a result to be entered but converts it to another value. This is particularly useful for results outside the range of an instrument, or a stable analytical range. For example, if the lower limit is set to 0.5 and 0.3 is entered, Matrix will convert the value and display it as <0.5. Similarly, if the upper limit is set, the value will be converted to a greater than value. The entered value is stored in the database but the displayed and reported values will be dependent on the rules set.
A test may have one or all the above actions defined, and each action can have different limits associated with it, therefore there may be multiple actions for each result. For instance, you may notify the user if the result is close to a limit but fail if the result is beyond the limit. A good LIMS will provide the choice of whether to just report the most severe action when multiple actions are triggered (i.e. reject, then fail, warning, and notification in order), or to report all failing actions to the user.
Matrix enables all Test, Substance and Sample limits to work in parallel, using a reporting hierarchy such that the reject parameters are checked first followed by the fail and warning parameters, and so on.
Complex Rule-Based Limits
Rule based limits build on the Test, Substance and Sample limits already discussed, allowing limits to be applied based on more complex rule-based criteria. These can be used to decide how a limit should be applied to a test based on information recorded about the sample. A practical example of this could be the situation where acceptable range for a blood test is different between different species of dog. The rule would be based on the species being tested. Similarly, the acceptable range for a hormone test may depend on the sex of the dog.
Summary
The use of limits of various types in LIMS is a powerful tool within the lab. It ensures that limits are applied consistently and that the right limits are applied to the right samples and tests. It also eliminates any potential user errors when assessing whether a result is within the defined limits or not. However, it is important that the application of limits within the context of a specific lab environment is carefully considered and planned. Ensuring that limits are correctly defined and used can bring major advantages to the laboratory organisation.
Further Information
A one-day system administrator training course is offered by Autoscribe Informatics allowing you to understand and be confident in setting and using all the different types of limits in your Matrix Gemini LIMS.
For further information please contact us.
