INTERNAL QUALITY CONTROL (IQC) AND PROBLEM SOLVING

SAIRI  SATARI

Biochemist
Part 1

RECTIFICATION IS ESSENTIAL, ALBEIT ROUTINE PROCEDURES

Internal Quality Control (IQC) is a process or system to monitor the quality of laboratory testing in terms of accuracy and precision. It includes pre-analytical and analytical phase. IQC should be able to detect the changing of systematic error and random error during the analytical process. Therefore, when we determine the target mean and SD or CV, the systematic error and random error should be taken into account. Drastic changes of the systematic error and random error will be affect the mean and SD or CV.

Target Mean, SD and CV will be change

Levey Jenning’s chart and Westgard rule are the common procedures used in the laboratories to determine the systematic error and random error.  The IQC must be compliance with the Wesgard rule before the patient results are released.

Usually, when we determine the target mean, SD or CV, we will collect 20 data point from selected level of quality control (QC) within 20 working days.  We calculate the mean, SD, and CV from the data. If the calculated mean is within the manufacturer’s mean range, then the mean and SD will be used as a target mean, and target SD. The target mean and SD will be stated in the Levey Jennings chart as mean ±2 SD (2 SD is 95% confident limit based on the normal distribution). The acceptability of our daily QC will be determine by Westgard rule.

The Levey Jenning’s chart and the Wesgard rule are based on the normal distribution. Thus, the setting of the target mean and SD or CV based on 20 data points only are not sufficient. The setting of target mean and SD or CV should take into account that the data collected should be in a normal distribution. Therefore, we must determine whether 20 data points will form a normal distribution or not. If not, we need to add more data until it forms a normal distribution.

The target mean and SD form manufacturer recommendation are wrong in term of setting procedure of the target mean and SD in the laboratory. We must calculate our target mean and SD based on our condition in the laboratory.

Levey Jenning Chart

When we perform repeatable analysis to the same QC lots, the data collected will generally be in a normal distribution but, we still have to prove that the data is in the normal distribution by ensuring that the mean, median and mode generate the same value. The target mean will reflect the systematic error and SD or CV will reflects the random error. Both of these errors will have to be consistent as long as we are using the same lot of QC in our analysis. Thus, the setting of the target mean and SD QC need to be based on the normal distribution at 95% confident limit or Mean ± 2SD. If the mean setting and SD is not based on the normal distribution, then we will have difficulty in solving QC non-compliance during analysis.

The Levey Jenning’s Chart and the Westgard Rule are based on the Normal Distribution and it can be help us to solve the problem for non-conformant daily QC.

TO BE CONTINUED