What should be done if scan values fall more than ±1.5% from the mean on a Shewhart plot?

• A. Ignore the readings and continue.
• B. Repeat the scan and, if still abnormal, call for service.
• C. Adjust the machine settings immediately.
• D. Document the readings and schedule a follow-up.

Answer: (B)

When scan values fall more than ±1.5% from the mean on a Shewhart plot, repeating the scan and, if the values remain abnormal, calling for service is crucial. This approach ensures that the integrity and accuracy of the bone densitometry measurements are maintained.

Shewhart plots are used in quality control to monitor the stability of a process over time. Values that fall outside of the defined control limits (in this case, ±1.5% from the mean) suggest that something might be amiss with the equipment or the procedure. By repeating the scan, the operator can determine whether the abnormal readings are a one-time occurrence or indicative of an underlying issue with the equipment. If the second scan still shows aberrant results, this warrants immediate attention from a qualified technician to evaluate and service the device, ensuring patient safety and the accuracy of future scans.

This procedure emphasizes the importance of quality control and maintaining accurate diagnostic procedures in medical settings, particularly in bone densitometry, where reliable data is crucial for assessing bone health.