Precision Study as per ISO 15189:2022 and CLSI Guidelines

A Precision Study is a method validation process used to evaluate how consistently a laboratory test produces the same result when the same sample is analyzed repeatedly under defined conditions.

In simple terms, precision measures the repeatability and reproducibility of a laboratory test.

If I analyze the same sample multiple times, I will get nearly the same result each time.

A test with high precision produces results that are very close to one another, indicating minimal random variation and reliable analytical performance.

Precision studies are a critical component of laboratory method validation and performance verification. They help ensure that test results are reliable, consistent, and suitable for clinical decision-making.

Conducting precision studies is recommended under internationally recognized quality standards such as ISO 15189:2022 and guidelines from the Clinical and Laboratory Standards Institute (CLSI), making them an essential part of laboratory quality management systems.

Why is a Precision Study Important?

A precision study helps laboratories:
Verify the reliability of new analytical methods
Evaluate instrument performance
Ensure consistent patient results
Meet accreditation requirements (e.g., NABL)
Detect random analytical errors

Without good precision, patient test reports may vary significantly even when there is no real change in the patient's condition.

Types of Precision

1. Repeatability (Within-Run Precision)

Also called intra-assay precision.

Same operator
Same instrument
Same reagent lot
Same day
Multiple repetitions

Example:

A glucose sample is tested 20 consecutive times on the same analyzer.

2. Intermediate Precision (Within-Laboratory Precision)

Also called between-run precision. Includes variations such as:

Different days
Different operators
Different reagent lots
Different calibration events

This reflects routine laboratory performance.

3. Reproducibility

Evaluates variation between:
Different laboratories
Different instruments
Different locations

Usually performed in multicenter studies or manufacturer validations.

How is a Precision Study Performed?

Step 1: Select Quality Control or Known samples

Use at least two concentration levels:

Normal level

Abnormal (high or low) level

Step 2: Perform Repeated Testing

Example protocol:

Test each QC level twice per day
Continue for 20 days

Total: 80 observations per QC level

Step 3: Record Results

Step 4: Calculate

Calculate:

Mean
Standard Deviation (SD)
Coefficient of Variation (CV%)

Formula:

CV (%) = (SD ÷ Mean) × 100

Example

Suppose glucose QC results are:

100, 101, 99, 100, 100

Mean = 100

Standard Deviation = 0.71

CV (%) = (0.71 ÷ 100) × 100

CV (%) = 0.71%

A low CV indicates excellent precision.

Interpretation

Precision vs Accuracy

A test can be:

Precise but not accurate

Accurate but not precise

Both accurate and precise (ideal)

Applications of Precision Studies

Precision studies are commonly performed for:

Clinical chemistry
Hematology
Immunoassays
Coagulation
Electrolytes
Molecular diagnostics
Point-of-care testing

Key Acceptance Criteria

A laboratory should compare its observed precision with:

Manufacturer's claimed precision
Internal quality goals
Biological variation–based specifications (where applicable)
Relevant laboratory policies and accreditation requirements

If the observed CV exceeds acceptable limits, the laboratory should investigate potential causes such as instrument issues, reagent variability, calibration problems, or operator technique.

Summary

A Precision Study evaluates the consistency and repeatability of laboratory test results by repeatedly analyzing the same sample under defined conditions. It helps identify random errors, demonstrates the reliability of an analytical method, and supports compliance with quality standards such as ISO 15189:2022. Precision is typically expressed using the Coefficient of Variation (CV%), where lower values indicate better analytical consistency.

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