Consider these case studies to avoid pre-analytical specimen errors
By Sheryl Whitlock, MA, MT(ASCP)BB
Case Study No. 1
The hematology instrument in the outpatient laboratory required replacement of the laser. Following the part replacement, the instrument was placed immediately back into service. Complete blood counts (CBCs) were performed and reported out. When the supervisor did a cumulative review of all results for the day, she noticed that all of the tests reported after the replacement maintenance had elevated eosinophils. She performed manual differentials on a representative sampling of these specimens. The results of the manual counts did not correlate with the elevated counts. What factor(s) may have contributed to this discrepancy?
In this instance, the machine is the issue. While most often one regards the machine as the analytical phase, it can play a role in a pre-analytical situation. The repairs were made pre-analytical and hence were the issue.
The analytical phase was the running of the instrument. While the physical running of the instrument was without issue, the pre-analytical steps caused the inaccuracies in the analyses. Whenever major repairs or adjustments are made on an instrument, calibration should be performed prior to testing patient samples. In addition, quality control (QC) samples should be tested. Neither calibration nor quality control was performed post-repair.
Additionally, there may have been some personnel issues. The personnel who are performing the testing did not perform the required steps necessary to assure that the test results would be accurate. Whether this was a training issue or a staffing/workload issue is not clear.
Case Study No. 2
You are a consultant for a local urgent care. When you make your regular visit to review quality control, the technologist working that day has a list of questions for you. Two of the issues and your observations are as follows:
The instrument that analyzes urine dipsticks is sporadically reporting positive leukocytes on patients. When then microscopic analysis is performed, correlation of white blood cells is not consistently present.
You review the operator's manual and observe the technologist perform two analyses. When you review maintenance logs, you note that there is a column for daily table cleaning that has not been completed for one week. Comparing frequency of actual cleaning to the operator's manual recommendations, you note that the manual recommends cleaning after each use.
Your observation of the technologist's operational methods does not reflect this practice.
Sedimentation rates for proficiency testing were all elevated on the last challenge. Again, you observe sedimentation rates being set up and read. You notice that the rack is seated on the top of a box on the counter. You also observe that the technologist did not check the level of the rack. Your observation is that the bubble in the leveling circle is positioned to the left of center.
In the case of the urine dipstick reader, the pre-analytical method is in error. Inadequate or incorrect preparation of instrumentation prior to analysis is imperative to proper operation. The inconsistent cleaning of the table did not comply with the operator's manual recommendations.
There most likely was cross contamination from previous urines with positive leukocyte results. It is imperative that all instrumentation be operated according to manufacturer's recommendations. Instruments that perform these pre-analytical preparation steps assist in maintaining compliance with proper operating technique.
Removal of the man (personnel) from the method will frequently reduce the number of errors. Personnel may have been an issue if the orientation/training of the technologist was inadequate or incomplete.
The sedimentation rack was tilted. This tilting caused the inaccurate results for the proficiency testing samples. In this case there were two categories of pre-analytical errors. Method was in error since the rack was not leveled. Measurement was in error since the leveling device of the rack was not assessed (measured) and appropriately adjusted (method) prior to testing.
Case Study No. 3
A hurricane has affected the local area. The entire city is without electricity. While the hospital is on emergency power, the number of "red" outlets is limited throughout the hospital. The external air conditioning unit was damaged in the storm and no air conditioning is available in the entire hospital.
Post-storm weather conditions include warm temperatures (> 90 degrees Fahrenheit during the daytime hours) and high humidity. Refrigerated materials have been consolidated into two small units within the laboratory while other less-sensitive items have been stored in the basement that has remained cooler. The following discrepancies have been noted:
The blood gas analyzer is sounding an alarm and reporting quality control values that are unacceptable.
The APTT determinations are prolonged on patients with no known risk factors.
A rapid strep determination has an unacceptable internal control in that the background does not clear.
What factors may have contributed to these issues?
In all three of these situations, the environment has impacted on the accuracy or efficacy of the test results. Instruments and test methodologies are designed for provision of accurate results when used within a narrow range of environmental parameters.
These parameters are assessed on a regular basis as a part of the quality control system. Temperature and humidity will impact on instrumentation, accurate test measurements, specimen integrity and the ability of a test method to perform in an acceptable manner. This is one of the reasons for monitoring, recording, and correcting of factors that adversely affect temperature and humidity in the testing environment.
The blood gas analyzer was most likely impacted by temperature and/or humidity that are out of the acceptable range for accurate performance. It is also possible that the control materials have been impacted by the same environmental factors.
The APTT determinations may have been impacted because the ambient temperature compromised the specimen integrity prior to analysis. Pre-analytical control of specimen temperature is crucial for accurate test results. Some parameters are more sensitive to temperature fluctuations than others.
The cartridges of the rapid strep kit may have been compromised by either temperature or humidity. The impact may have occurred either during storage or the actual testing process. Effects of specimen storage are pre-analytical in nature, while the impact of temperature or humidity during the test procedure would be a factor in the analytical process.
As this series has emphasized, pre-analytical variables are many, varied and not always discernible. When deciding if the errors are pre-analytical or analytical decide if the step(s) that caused the inaccuracy were involved in or important for preparation. If so, then the phase of testing that impacted on the test results was pre-analytical.
In summary, pre-analytical variables may be categorized as:
- Instruments (machines), and
These same variables may be used to evaluate any type of multi-step process. Each variable will have a different impact. At times, a single pre-analytical variable will be the cause of inaccuracies or breach of specimen integrity. At other times, "finger pointing" to a single source of error is not possible. Multiple pre-analytical factors often impact on the system.
There is no set formula or guidelines for assessing and/or correcting pre-analytical variables. As is the case in much of laboratory medicine, a case-by-case analysis is required to have your "finger" on the pulse of your pre-analytical system.
Sheryl Whitlock is laboratory coordinator, Student Health Service, University of Delaware at Newark.
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