Quality Control & Westgard Rule in Clinical Chemistry

Quality control in clinical chemistry testing is crucial for ensuring accurate and reliable results, ultimately improving patient care and safety. It helps detect and correct errors in the analytical process, validates instrument performance, and verifies the accuracy and precision of test results. By maintaining QC, laboratories can provide clinicians with trustworthy information for diagnosis, prognosis, and treatment planning. 

In Clinical Laboratory work, the operator often faces the errors like;

Analytical Errors which may occur due to Instrument malfunction or reagent issues.

Systematic Errors which are consistent deviations from the true value which may happen due to factors like calibration misalignment. 

Random Errors which are unpredictable but can affect the precise outcome of testing.

Under the circumstances by applying the correct QC practices in Laboratory Work it ensures Accuracy & Precision, Validate Instrument, and reagent performance, enhance patient safety by providing True Values of testing. This system further helps for accurate diagnosis and help in reducing risk of harm which may occur due to erroneous diagnosis.

The effective quality management in a clinical chemistry laboratory must include reliable systems that can protect the outcomes of laboratory testing from irreversible errors. Thus, the purpose of analytical quality control (AQC) is to ensure calibration between instruments, devices, and data systems. It also helps to maintain accuracy and precision through all stages of the analytical process, from sampling to reporting.  

QC samples used for IQC (Internal Quality Control) are expected to be identical and tested identically to patient samples. The purpose of repeated quality control testing is to validate precision and accuracy of the results of patient sample testing. Precision is the “degree of agreement among repeated measurements of the same characteristic on the same sample, while accuracy is how close results are to what is expected from a test.

Peer Testing and monthly review of QC trends are also often used to manage the QC. Clinical laboratories are frequently enrolled in clinical laboratory proficiency testing (PT) programs that are used to validate their testing protocols. These programs, are utilized not only to validate laboratory testing but to validate personnel training and procedures.

One of the most common tools used to track laboratory quality control samples is the Levey-Jennings (L-J) chart. An L-J chart and the Westgard Rules are frequently used to verify trends, biases, or errors in quality controls. The Westgard Rules observe the normal distribution expected and identify standard deviations produced. Implementing Westgard rules within an L-J chart can identify violation of the rules based on control limits established for the sample tested.

Many laboratories utilize L-J charts for 14- or 30-day reviews of QC testing. While daily identification of QC deviations from normal ranges ensures accuracy of sample testing, longer-term reviews are more beneficial to diagnose trends and biases in tests which could be missed daily. An additional use of the L-J chart without quality control samples is to utilize patient samples as their own controls. By tracking the running averages of the patient results, a laboratorian can identify drift or problems with analyser function that may not captured by quality control testing.

In conclusion, management of quality control can ensure accuracy and precision of both quality and patient results. The focus on trends and biases is a good identification of potential changes in results that can affect accuracy of overall results. Also, management of matrix effects and calibration misalignment are important aspects to observing shifting L-J charts and adjustments of accuracy over time. Continuous monitoring of quality control testing and capture of biases or trends are important to ensure accuracy of patient test results which is the prima phase requirement of Laboratory work.