AACC 2017 Poster:
Title: The impact of TEa selection on patient risk: Setting Limits of Medical Utility
Authors: Zoe Brooks, George Sweeney
Permanent Number: B-201
Poster Session Day: Wednesday, August 2, 2017
Poster Session Number / Day: Session B: 9:30 am – 5:00 pm
Attendance Time: 12:30 pm – 1:00 pm
- To demonstrate the relationship between the laboratory selection of TEa limits, patient risk and clinical costs
- To compare QC data for calcium to CLIA limits, Biological Variation and NIST medical goal.
The allowable total error is equivalent to the error that does not significantly contribute to wrong clinical decisions. (ISO 15189:2012 Medical laboratories – Requirements for quality and competence). To evaluate risk, laboratories must “compare the estimated risk against given risk criteria to determine the acceptability of the risk” (CLSI EP 23-A). Current TEa limits are typically selected within the laboratory as CLIA or BV limits. Neither of these may be appropriate as a ‘Limit of medical utility”. Selection of TEa limits drives the perceived and factual acceptability of patient risk. Medical goals represent best practice.
- We created 3 data sets of recently
- 1. measured mean;
- 2. measured SD and
- 3. Peer Mean with sigma values of 5.7, 5.2 and 3.3.
- We entered the data in CatalystQC software with
- CLIA limits of 0.25 mmol/L (1.0 mg/dL),
- NIST-recommended Medical goal of 0.125 mmol/L (0.5 mg/dL) mg/dL and
- biological variation desirable TEa of 2.55%
- We calculated a z-value as (|measured mean – TEa limit|)/SD – equivalent to sigma metric as (TEa-|bias|)/SD
- We converted the z-value to percent risk level plus the number and clinical/legal cost of medically-unreliable results (MURs)/year at this level of accuracy and precision
- We compared the interpretation of acceptability of quality and probable action based on the selected TEa limits
Below is a table of the results of the study. The data used is the same within each case, only the TEa is changed within each case.
We see that by only changing TEa values there is a significant change in patient risk and clinical cost. Looking at case 1 as an example, the medical and legal cost can go from $0 with a TEa of 1.0 mg/dL using CLIA limits to a cost of $320,900 for the year using biological variation desirable TEa of 2.55%.
The patient risk goes from a predicted 0 medically-unreliable results with CLIA to 3,209 patients at risk using the biological variation TEa.
Comparing the results of evaluation with CLIA, Medical, and Biological Variance demonstrates that the value selected for TEa will play a major role in clinical acceptability, patient risk, and cost due to medically unacceptable errors. The TEa should be validated to be certain that the risk and cost is minimized.