QL Limit of Detection

QL Limit of Detection

Qualitative Limit of Detection

Overview

Other Names - Sensitivity Limit, Detection Threshold, Minimum Detectable Concentration, Analytical Sensitivity.

The Qualitative Limit of Detection (LoD) refers to the lowest concentration of an analyte that can be reliably distinguished from the absence of that analyte (a blank sample) but not necessarily quantified. It is a critical parameter in method validation, ensuring that the method can detect even the smallest amounts of the substance of interest.

Definitions

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**Cualia Support Docs Definitions (Public)**

Name
Definition
Agreement

Whether two values, usually the actual and reference values acceptably agreeable, based on testing requirements and/or Error Allowance.

Agreement Percent

The percentage (%) of paired Results within Agreement amongst the number of Samples measured. Agreement %=(Results in AgreementTotal Number of Comparisons)×100\text{Agreement \%} = \left( \frac{\text{Results in Agreement}}{\text{Total Number of Comparisons}} \right) \times 100 See: Agreements

Agreements

The total number of measurements between actual and reference value in agreement.

Between Day/Run

Comparison of Run replicate measurement(s) that occur on different runs/days. Other Names → Inter-Assay

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.

Limit of Detection (LoD) Experiment

An MV Experiment used to determine the lowest "reliable" value measured from a test

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.

Minimum Detectable Concentration (LoD)

The lowest concentration of an analyte that can be reliably detected by a test, distinguishing it from zero or background noise.

Qualitative

A Result Type for a Test that can only have two possible options

Qualitative Agreement

In Qualitative testing a matching pair of Actual and Reference Results are considered in Agreement

Reference Value

The value/result that represents the true value from a trusted reference source such as a verified instrument, EQA, or a commercial product.

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.

What is the Limit of Detection (LoD) Experiment?

The Limit of Detection (LoD) experiment in Method Verification (MV) assesses the lowest concentration of an analyte that can be reliably detected by the test method. This experiment involves testing samples with progressively lower concentrations of the analyte until the method can no longer distinguish the analyte from a blank sample. The LoD is crucial for determining the method's sensitivity, ensuring that it can detect low levels of the analyte accurately.

This experiment typically involves running multiple replicates of a low concentration sample and analyzing the results to identify the lowest concentration at which the analyte can be consistently detected. The LoD provides valuable information about the method's capability to detect low-level analytes, which is essential for early diagnosis and monitoring in clinical settings.

How to Perform Qualitative Limit of Detection Experiments

1. Define Acceptance Criterias

Days and Results 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.

Min Between Day Agreement (%)

The Min. Between Day Agreement % is the Agreement % for the sample across all of its days and replicates.

The 95% agreement threshold is widely recommended in MV experiments to ensure that the new method reliably matches the reference method. This level of agreement is chosen because it strikes a balance between clinical significance and statistical reliability.

Specifically, the Bland-Altman method, which is a commonly used approach for assessing agreement, calculates the 95% limits of agreement as the mean difference plus and minus 1.96 times the standard deviation of the differences. This approach ensures that 95% of the differences between the new method and the reference method fall within these limits, providing a high degree of confidence that the two methods produce comparable results in most cases.

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2. Sample Selection

For LoD experiments, use a control with a known low concentration that consistently yields a positive result.

3. Testing Samples

Measure the sample multiple times across different days and analyze the results to determine the lowest concentration reliably detected. Ensure variations in time of day and operator to rule out biases.

4. Use the Cualia MV App

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

Reference Methods

Reference Methods are well-established, highly accurate, and precise analytical procedures used as standards to evaluate the performance of other methods.

For testing you will need to select a Reference Method to act as your reference result to match with the actual results of the new test.

It is recommended to use a validated and verified source of the same model/make as the analyzer being tested to ensure compatibility of the measurements.

Data Table

Minimum Detectable Concentration Field

Minimum Detectable Concentration (MDC) is the lowest concentration of an analyte that can be reliably detected by a test, distinguishing it from zero or background noise. It is a critical parameter in assessing the sensitivity of a test.

In Limit of Detection (LoD) MV experiments, MDC is verified to establish the test's ability to identify low levels of an analyte accurately.

Table Columns

There are 4 relevant columns types in the Qualitative LoD 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 1 to X | Pos or Neg Label only - The measured value of the replicate.

Result | Read Only - Indicates whether the Within-Day results are within agreeable range.

(blank) - No result. The sample is likely to be ineligible for calculation because it is missing an actual and/or reference value.

(✓) → The individual result is out of agreement range and/or the run is not within agreeable parameters

(✓) → The individual result is out of agreement range however the run/day is still within agreeable parameters

(✓) → The individual result is within agreeable parameters (pass)

Qualitative Limit of Detection Results

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

Name
Definition
Result(s)

A value or determination collected by measurement or calculation.

Agreement

Whether two values, usually the actual and reference values acceptably agreeable, based on testing requirements and/or Error Allowance.

Agreements

The total number of measurements between actual and reference value in agreement.

Agreement Percent

The percentage (%) of paired Results within Agreement amongst the number of Samples measured. Agreement %=(Results in AgreementTotal Number of Comparisons)×100\text{Agreement \%} = \left( \frac{\text{Results in Agreement}}{\text{Total Number of Comparisons}} \right) \times 100 See: Agreements

Qualitative Limit of Detection Acceptance

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To pass the LoD experiment, the Agreement (%) of positive measurements must satisfy the Min. Agreement acceptance criteria.

Limit of Detection

The Minimum Detectable Concentration evaluated by the LoD experiment.

Results

Results - The total number of measurements collected. This value will be yellow if it doesn’t satisfy the requirements of the acceptance criteria and green when it passes.

Agreement

Agreement - The proportion (%) of test results that match the reference results. In the results bar, the color will be green and be considered passed when it satisfies the Min. Agreement or Min. Between-Day Agreement acceptance criteria.

Sources

Cualia Support Docs Citations

Source
Bland, J. M., & Altman, D. G. (1986). Statistical methods for assessing agreement between two methods of clinical measurement. Lancet, 327(8476), 307-310.
Clinical and Laboratory Standards Institute (CLSI). (2016). EP17-A2: Evaluation of Detection Capability for Clinical Laboratory Measurement Procedures; Approved Guideline—Second Edition. Clinical and Laboratory Standards Institute.
International Organization for Standardization (ISO). (2015). ISO 15189:2012 Medical laboratories — Requirements for quality and competence. International Organization for Standardization.