Category: Basic QC Concepts | Estimated reading time: 7 minutes
The Scenario That Happens in Every Laboratory
New reagents arrive. New control materials are also here. The kit insert shows a range: 90–130 mg/dL.
The question is simple: do we immediately use the manufacturer's range?
Why Manufacturer Ranges Cannot Be Used Directly
The answer is: no — and this is not just a matter of formal procedure. There is a solid scientific reason behind it.
The range listed in the manufacturer's kit insert is established based on testing at their production facilities — using instruments, reagents, operators, room temperatures, and environmental conditions that may differ significantly from our laboratory's conditions. The difference between the manufacturer's target value and the target value independently established by the laboratory can be quite significant — even for instruments and reagents from the same brand. This is not a mistake by the manufacturer, nor is it a mistake by the laboratory. It is a consequence of the fact that every measurement system is unique, and its performance is influenced by a specific combination of all variables within that laboratory.
There are three main sources of variation that cause this:
Instrument variation. Two instrument units of the same model from the same factory will not produce exactly identical values. There is reasonable manufacturing variation — and that small difference can be consistent in one direction, creating a systematic bias that would not be detected if we used the manufacturer's range.
Operational condition variation. Laboratory room temperature, humidity, the quality of water used in reagents, and even how control materials are prepared and reconstituted — all of these consistently affect measurement results.
Operator variation. Pipetting techniques, slightly different incubation times, and the sequence of steps that are not always identical between operators — all contribute to performance characteristics that are unique to that laboratory.
Westgard (2016) emphasizes that the Target Value (TV) and SD used in a QC system must be established by the laboratory itself — not taken from the kit insert. Using manufacturer ranges as control limits is one of the most common mistakes that makes a QC system insensitive, or conversely, results in too many false alerts.
Three Points That Need to Be Internalized
"Manufacturer ranges are made for a general population, not our laboratory's specific instrument conditions." This is a statement about context. The manufacturer's target value is the central value of the distribution of results they obtained under their conditions. The distribution we have in our laboratory will be different — and the control limits must reflect that distribution, not someone else's.
"Our temperature, humidity, operators, and instruments can differ from the manufacturer's reference lab." This is a statement about sources of variation. Each of these factors contributes to the unique performance characteristics of the instrument in our laboratory. Ignoring these differences means ignoring the reality of our own measurement conditions.
"We need to establish our own laboratory's Target Value (TV) and SD — through Preliminary Testing." This is a statement about the solution. And the solution is Preliminary Testing, a four-step procedure that establishes the TV and SD based on the actual conditions of the laboratory.
Practical Implications That Are Often Overlooked
There is one situation that is very common in laboratories and accurately illustrates the consequences of not doing this correctly.
A laboratory receives a new reagent lot from the same manufacturer. Because it is still the same brand, no one feels the need to perform verification. QC is immediately run using the old control limits. A week later, there are slightly more QC results that are "close" to the upper limit — but none exceed the limit, so no one reacts.
A month later, in the monthly evaluation, it is observed that the average QC result has shifted about 4% higher than the previous month. The new reagent lot has slightly different characteristics — and that shift has been occurring for a month without being detected because the control limits being used did not respond to this change.
Verification of result consistency during reagent lot changes is not just an optional best practice — CLSI specifically published the EP26-A guideline for this purpose, which provides a practical protocol for laboratories to evaluate the consistency of patient results when a new analytical reagent lot replaces the lot currently in use. Braga & Panteghini (2020), in their review of measurement uncertainty in medical laboratories, also emphasize that performance verification during changes in analytical conditions — including reagent lot changes — is an essential component of a reliable quality system.
A Question That Opens the Next Discussion
This scenario is not just a technical question about control materials. It is a question about habits and systems:
"In your lab, every time there is a new reagent lot — is there a verification procedure that is consistently carried out? Or is it used immediately?"
If the answer is used immediately — you are not alone. This is a very common practice, especially in laboratories with limited resources and high work volumes. But understanding why verification is important is the first step toward building a different habit — step by step, in a way that can be implemented even in laboratories with resource limitations.
Closing
Manufacturer ranges are a useful starting point — but they are not the end point. They provide an overview of where control values should generally be. But an effective QC system requires more than that — it requires a Target Value and SD that reflect the actual conditions of our own laboratory.
Establishing those values is the responsibility of the laboratory. And the procedure for doing so is called Preliminary Testing.