QNT Limit of Blank

QNT Limit of Blank

Quantitative Limit of Blank (LoB)

Overview

Other Names - Detection Threshold, Analytical Blank, Blank Limit, Decision Threshold, LOD Precursor, Negative Control Limit, Blank Cutoff, LoB, Threshold of Detection, Signal-to-Noise Limit, Analytical Sensitivity Threshold, Background Limit, Non-Detect Threshold

The Limit of Blank (LoB) experiment determines the highest measurement value expected when testing a blank sample, which contains no analyte. This threshold distinguishes between a true absence of analyte and background noise, setting a baseline above which measurements indicate potential analyte presence.

Definitions

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

Name
Definition
Blank

A sample of similar matrix to method's expected sample with none of the analyte present. Oftentimes this can be a zero standard from a calibrator.

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 Blank (LoB) Experiment

An is the highest concentration of analyte detected for a blank sample. This can be determined through the LoB MV Experiment. LoB=μ+1.645×σLoB=μ+1.645×σ μμ: Mean of the results σσ: Standar Deviation of results

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.

What is the Limit of Blank Experiment?

The Limit of Blank (LoB) experiment is a fundamental assessment in laboratory diagnostics used to identify the threshold between noise (background signals) and an actual analyte presence in a sample. In analytical testing, particularly when dealing with low concentrations of substances, it’s crucial to differentiate between measurements that result from true analyte presence and those due to random background variation.

The LoB represents the highest value one can expect from measurements of a blank sample (i.e., a sample with no analyte). Any result above this threshold suggests the possible presence of the analyte, though it does not confirm its quantifiable detection.

  1. Mean of Blank Measurements (μ​): This is the average measurement obtained from multiple blank samples. It represents the baseline response in the absence of analyte.
  2. Standard Deviation of Blank Measurements (σ): This quantifies the variability or "noise" in the blank measurements.

Using these values, the LoB is calculated as:

LoB=μ+1.645×σLoB=μ+1.645×σ

μμ: Mean of the results

σσ: Standard Deviation of results

Calculated LoB must be less than the Reference LoB for the experiment to pass.

The constant 1.645 reflects the 95th percentile of a one-sided normal distribution, meaning there’s a 5% probability that a blank sample’s signal might exceed this threshold due to random variation alone.

The LoB experiment is the first step in a broader sensitivity analysis often followed by the Limit of Detection (LoD) and Limit of Quantitation (LoQ). Each step progressively refines the threshold and measurement precision required to reliably detect and quantify low levels of analyte with statistical confidence.

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.

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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.

3. Testing Samples

Measure a single blank 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 in Limit of Blank experiments

LoB=μ+1.645×σLoB=μ+1.645×σ

μμ: Mean of the results

σσ: Standard Deviation of results

Calculated LoB must be less than the Reference LoB for the experiment to pass.

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
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.

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.

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.

Replicate

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

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.

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.

Blank

A sample of similar matrix to method's expected sample with none of the analyte present. Oftentimes this can be a zero standard from a calibrator.

Experiment

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

Mean (x̅)

Average value amongst a sample group

Limit of Blank (LoB) Experiment

An is the highest concentration of analyte detected for a blank sample. This can be determined through the LoB MV Experiment. LoB=μ+1.645×σLoB=μ+1.645×σ μμ: Mean of the results σσ: Standar Deviation of results

Label

The general identification used to identify a specific Sample.

Method Validation

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

Run

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

Experiment Pass / Fail

Sample Results

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For a Limit of Blank experiment to pass, the calculated LoB must be below the manufacturer’s reference LoB.

Experiment Settings and Acceptance Criterias