QNT Limit of Quantitation

QNT Limit of Quantitation

Quantitative Quantitation (LoQ)

Overview

Other Names - Quantification Limit, Quantitation Threshold, LOQ, Lower Limit of Quantification, Minimal Quantifiable Level, Quantifiable Detection Limit, Minimum Quantitation Limit, Reliable Detection Threshold, Reporting Limit, Quantitative Detection Limit

The Limit of Quantitation (LoQ) experiment determines the lowest concentration of an analyte that can be reliably quantified with acceptable precision and accuracy. This threshold ensures that measured values are both detectable and reproducible, allowing for reliable reporting in diagnostic and analytical testing.

Definitions

🗣️
**Cualia Support Docs Definitions (Public)**

Name
Definition
Bias

The difference in Results when comparing laboratory Quantitative methods with established methods.

Days (MV Experiments)

Days refers to the number of distinct days on which a test is repeated to assess the consistency of results over time.

Eligible (Sample and Results)

Samples that provide the necessary information for statistical calculations to be performed. Usually this is possessing both an actual and expected result.

Experiment

A sampling of results that are statistically analyzed and interpreted in the evaluation of testing performance.

Label

The general identification used to identify a specific Sample.

Limit of Quantitation (LoQ) Experiment

An MV Experiment used to determine the lowest amount of analyte that can be reliably determined.

LoQ Allowable Error % (k)

LoQ Allowable Error (k) sets the LoQ precision by scaling the LoQ Reference Value. With a general standard of 10%, a higher value increases statistical confidence.

LoQ Error Allowance

A calculated value from the LoQ Allowable Error % (k) and the LoQ Reference Value which returns the maximum TE result acceptable from an LoQ Experiment. LoQ Allowable Error %=Reference LoQ Value×k100LoQ\ Allowable\ Error\ \% = Reference\ LoQ\ Value \times \frac{k}{100} Reference LoQ Value: The validated LoQ concentration determined during validation k: LoQ Allowable Error

LoQ Reference Value

The manufacturer stated LoQ determined through validation.

Mean (x̅)

Average value amongst a sample group

Method Validation

A systematic process to evaluate whether the performance of a medical Test meets quality goals to be used for medical testing.

Method Verification

A systematic process to evaluate whether the performance of a medical Test meets quality goals set by a validation. Performance evaluations may usually be found in a manufacturer insert.

Replicate

Multiple tests on the same sample to assess precision and repeatability, conducted within a run or across multiple runs.

Result(s)

A value or determination collected by measurement or calculation.

Results per Day (MV Experiments)

In MV experiments, the Results Per Day is the number of replicate measurements that will be taken per day.

Run

A sequence of measurements on a set of samples under the same conditions, performed within a defined time period.

Sample(s)

Individual specimens collected for testing representing the source. In MV experiments with Runs, this can refer to to the number of concentration levels used.

Standard Deviation (σ or StdDev)

Statistical measure of the amount of variation from the mean. σ=1n−1∑i=1n(xi−xˉ)2\sigma = \sqrt{\frac{1}{n-1} \sum_{i=1}^{n} (x_i - \bar{x})^2} σ = Standard Deviation n = Sample Size xix_i = Individual data point xˉ\bar{x} = Mean

Total Error (for LoQ)

Total Error for LoQ represents the calculated error at the low concentration. TE=σ+2×BiasTE=σ+2×Bias σ: Standard Deviation of the results Bias: Difference between mean of samples and reference value

What is the Limit of Quantitation Experiment?

The Limit of Quantitation (LoQ) experiment determines the lowest concentration at which an analyte can be reliably measured with accuracy and precision, ensuring results are suitable for diagnostic or clinical interpretation. Unlike the Limit of Detection (LoD), which merely confirms the analyte’s presence, the LoQ guarantees that measured values can be quantified with dependable accuracy and reproducibility. This threshold is critical in tests where low analyte levels need accurate quantification to support medical decisions or research findings.

LoQ is done for tests that require accuracy and precision at very low levels and can be

To determine the LoQ, a low-concentration sample is selected, typically close to the expected threshold of clinical interest.

Testing is conducted over several days, often spanning three to five separate days, to capture any variations that might arise due to environmental changes, operator differences, or minor fluctuations in the instrument. This multi-day approach ensures that results represent consistent and accurate performance under realistic laboratory conditions.

Experiment Settings and Acceptance Criterias

1. Define Acceptance Criterias

Days and Results/Replicates per Day

The number of days and measurements per day that will be performed for each sample/level. It is best to use a number of days and results per day that will effectively evaluate the precision of your instrumentation.

Set the LoQ Allowable Error

The LoQ Allowable Error sets the LoQ precision by scaling it to a percentage of the LoQ Reference Value

The default LoQ based on the widely accepted standard is set to 10%.

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2. Sample Selection

In general practice is it often acceptable to use controls as samples. However this should be discussed with the assessor to confirm.

Select a low concentration sample of known Reference value to compare with the LoQ Reference Value

3. Testing Samples

Enter in the LoQ reference value above the Data Table which will be used for comparison of the sample results.

Measure the sample on your new instrumentation (actual), conducting it based on your acceptance criteria. For example a 3 day 5 replicate (3x5) structure will mean to run the blank on 3 separate days, 5 times each day.

To ensure robustness and reduce potential operator bias, vary the time of day and operators performing the measurements. This approach helps confirm that observed variability in blank measurements represents genuine background noise rather than inconsistencies in the testing process.

4. Use the Cualia MV App

Make sure the data is entered into the experiment with the right acceptance criterias.

Data Table

Run | Free Text - This column identifies the run that the replicate group was measured. It represents Within-Day/Run combined results. The default value is the Day number.

Replicate(R) 1 to X | Number only - The measured value of the replicate. A color may indicate whether the result is within agreeable parameters.

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Calculations

A minimum of 3 results are required for calculating results

LoQ Allowable Error %

LoQ Allowable Error %=Reference LoQ Value×k100LoQ\ Allowable\ Error\ \% = Reference\ LoQ\ Value \times \frac{k}{100}

Reference LoQ Value: The validated LoQ concentration determined during validation

k: LoQ Allowable Error

LoQ Total Error (TE)

TE=σ+2×BiasTE=σ+2×Bias

σ: Standard Deviation of the results

Bias: Difference between mean of samples and reference value

Standard Deviation (σ or StdDev)

Standard Deviation (σ or StdDev) - The statistical measure of the amount of variation from the mean.

σ=1n−1∑i=1n(xi−xˉ)2\sigma = \sqrt{\frac{1}{n-1} \sum_{i=1}^{n} (x_i - \bar{x})^2}

σ = Standard Deviation

n = Sample Size

xix_i = Individual data point

xˉ\bar{x} = Mean

Results

🗣️
**Cualia Support Docs Definitions (Public)**

Name
Definition
LoQ Error Allowance

A calculated value from the LoQ Allowable Error % (k) and the LoQ Reference Value which returns the maximum TE result acceptable from an LoQ Experiment. LoQ Allowable Error %=Reference LoQ Value×k100LoQ\ Allowable\ Error\ \% = Reference\ LoQ\ Value \times \frac{k}{100} Reference LoQ Value: The validated LoQ concentration determined during validation k: LoQ Allowable Error

LoQ Reference Value

The manufacturer stated LoQ determined through validation.

Total Error (for LoQ)

Total Error for LoQ represents the calculated error at the low concentration. TE=σ+2×BiasTE=σ+2×Bias σ: Standard Deviation of the results Bias: Difference between mean of samples and reference value

LoQ Allowable Error % (k)

LoQ Allowable Error (k) sets the LoQ precision by scaling the LoQ Reference Value. With a general standard of 10%, a higher value increases statistical confidence.

Bias

The difference in Results when comparing laboratory Quantitative methods with established methods.

Mean (x̅)

Average value amongst a sample group

Standard Deviation (σ or StdDev)

Statistical measure of the amount of variation from the mean. σ=1n−1∑i=1n(xi−xˉ)2\sigma = \sqrt{\frac{1}{n-1} \sum_{i=1}^{n} (x_i - \bar{x})^2} σ = Standard Deviation n = Sample Size xix_i = Individual data point xˉ\bar{x} = Mean

Quantitative Limit of Blank Acceptance

Sample Results

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For a Limit of Quantification experiment to pass, the calculated TE must be below the LoQ Error Allowance.