Troubleshoot QC Results

Inevitably, a QC system will indicate an out-of-control situation. What does a laboratory do then? In a lesson titled "QC–The Out-of-Control Problem," Elsa F. Quam BS, MT (ASCP) describes two common bad habits and provides five good habits to use when troubleshooting QC results.

Repeat the Control

Laboratories often apply the 1_2s rule, which yields a false rejection rate of 5% for N=1, 9% for N=2, and 14% for N=3 (where N is the number of control materials tested in the run).

When using the 1_2s rule, some laboratories think it is reasonable to simply repeat the test for the control. However, with carefully chosen SPC rules, this approach is unnecessary. As an example, consider that the false rejection rate for a 1_3s rule is only 0.3%. It is also important to remember that even if the repeat value is within control limits and the run is accepted, it is possible that a problem is being ignored until a future run.

Try a New Control

Another bad habit is to test a different vial of control and repeat the testing until it falls within an acceptable range. Although a bad vial of control material is unlikely, it can occur. For example, controls are not properly reconstituted, are stored improperly, are used beyond their expiration date, and so on. Training can address these issues. Cost is another issue. A new vial of control material is usually much less expensive than repeating a patient run.

As Ms. Quam concludes, "Automatically repeating controls or blaming the control itself are often attempts to resolve the problem without the hassle and time delay necessary in finding and eliminating the true cause of the QC failure. These practices have become habit because they are easy and we often do not have or do not teach the skills necessary to resolve the problem using a more systematic approach."

Recalibrate

Although not mentioned in Ms. Quam's lesson, another bad habit is frequent recalibration. It is important to be concerned about the number of times a test is recalibrated as each calibration or recalibration potentially introduces new or additional systematic errors. Frequent recalibration can indicate a defective SPC protocol (rules applied, mean, and range in use), instrument malfunction, sub-optimal reagent quality, or failure to follow the manufacturer's instructions and schedule for maintenance.