Accuracy and precision are fundamental aspects of bioanalytical assay validation. Accuracy refers to how close the measured values are to the true or reference values, while precision assesses the consistency of measurements when repeated under the same conditions. Here's how accuracy and precision are typically performed and evaluated:
Accuracy:
Reference Standard: A certified reference standard of the analyte is used to establish the true concentration. The reference standard's concentration is accurately known and traceable to a recognized standard.
Spiking: A set of samples containing the analyte at various concentrations is prepared by spiking known amounts of the reference standard into a matrix that closely resembles the samples being analyzed.
Analysis: Both the spiked samples and the unspiked samples (blank matrix) are analyzed using the bioanalytical assay. The goal is to measure the analyte's concentration accurately.
Calculation: The accuracy is calculated by comparing the measured concentrations of the spiked samples to the known reference standard concentrations. Accuracy is expressed as a percentage recovery, where recovery close to 100% indicates high accuracy.
Acceptance Criteria: Regulatory guidelines or predefined criteria determine acceptable accuracy ranges. The assay's accuracy should fall within these ranges for reliable data interpretation.
Precision:
Replicate Analysis: Multiple aliquots of the same sample are analyzed in a single analytical run or across multiple runs. Each aliquot is treated as an independent measurement.
Calculation of Variability: The variability of the measurements is assessed through statistical analysis. Common parameters used to assess precision include the standard deviation (SD), coefficient of variation (CV), and relative standard deviation (RSD).
Within-Batch Precision (Repeatability): Within a single analytical run, the precision is evaluated by calculating the SD, CV, or RSD of the measurements from replicates of the same sample.
Between-Batch Precision (Intermediate Precision): Precision is evaluated by analyzing replicates of the same sample across multiple analytical runs. The SD, CV, or RSD is calculated to assess the variability across different days or instruments.
Acceptance Criteria: Similar to accuracy, predefined acceptance criteria or regulatory guidelines dictate acceptable precision levels. Lower variability (smaller SD, CV, or RSD) is desirable for reliable and reproducible results.
Evaluation of System Suitability:
System suitability tests ensure that the analytical system is performing as expected. These tests may include analyzing quality control samples across the analytical run to ensure consistent performance.
Data Interpretation: The precision assessment helps researchers understand the level of variability inherent in the assay. High precision indicates that the assay can produce consistent results under the same conditions.