Top-down and bottom-up approaches for the estimation of measurement uncertainty in coagulation assays

Bias in Laboratory Medicine: The Dark Side of the Moon

Physicians increasingly use laboratory-produced information for disease diagnosis, patient monitoring, treatment planning, and evaluations of treatment effectiveness. Bias is the systematic deviation of laboratory test results from the actual value, which can cause misdiagnosis or misestimation of disease prognosis and increase healthcare costs. Properly estimating and treating bias can help to reduce laboratory errors, improve patient safety, and considerably reduce healthcare costs. A bias that is statistically and medically significant should be eliminated or corrected. In this review, the theoretical aspects of bias based on metrological, statistical, laboratory, and biological variation principles are discussed. These principles are then applied to laboratory and diagnostic medicine for practical use from clinical perspectives.

Measurement uncertainty

Over time, the metrological concept of uncertainty in measurement has been very successfully integrated into laboratory sciences. For proper implementation, an understanding of specific metrology terminology and additional concepts such as metrology traceability and commutability is necessary. Although the original thinking about measurement uncertainty in laboratory medicine suggests the complexity of the concept, it basically refers to the result as the end product of the entire laboratory process. Although the data on measurement uncertainty can be expressed quantitatively, the basis of this concept is the continuous evaluation of all phases of the laboratory process. This means that laboratory experts should keep in mind that the extra-analytical phases (on which the uncertainty of the measurement results may depend the most) must be continuously monitored. The analytical phase can be "held in check" by established internal and external quality control processes. It is the internal/external quality control data that is used to calculate the numerical value of the measurement uncertainty of the measurement results. Although over time the awareness of laboratory experts regarding the concept of measurement uncertainty has increased, there are still many challenges that need to be followed, and the last one is how to achieve a balance between understanding, evaluation process and application of measurement uncertainty data of measurement results for complete and ultimate practical use.

Estimating the measurement uncertainties of the international sensitivity index of 12 thromboplastins through Monte Carlo simulation

BACKGROUND

Measurement uncertainty (MU) estimation has become an important process in clinical laboratories; however, calculating the MUs of the international sensitivity index (ISI) of thromboplastins is difficult because of the complex mathematical calculations required in calibration. Therefore, this study quantifies the MUs of ISIs through the Monte Carlo simulation (MCS), which involves random sampling of numerical values to solve a complex mathematical calculation.

METHODS

Eighty blood plasmas and commercially available certified plasmas (ISI Calibrate) were used to assign the ISIs of each thromboplastin. Prothrombin times were measured using reference thromboplastin and 12 commercially available thromboplastins (Coagpia PT-N, PT Rec, ReadiPlasTin, RecombiPlasTin 2G, PT-Fibrinogen, PT-Fibrinogen HS PLUS, Prothrombin Time Assay, Thromboplastin D, Thromborel S, STA-Neoplastine CI Plus, STA-Neoplastine R 15, and STA-NeoPTimal) with two automated coagulation instruments: ACL TOP 750 CTS (ACL TOP; Instrumentation Laboratory, Bedford, MA, USA) and STA Compact (Diagnostica Stago, Asnières-sur-Seine, France). Then, the MUs of each ISI were simulated through MCS.

RESULTS

The MUs of ISIs ranged from 9.7 % to 12.1 % and 11.6 % to 12.0 % when blood plasma and ISI Calibrate were used, respectively. For some thromboplastins, the ISI claimed by manufacturers significantly differed from the estimated results.

CONCLUSIONS

MCS is adequate to estimate the MUs of ISI. These results would be clinically useful for estimating the MUs of the international normalized ratio in clinical laboratories. However, the claimed ISI significantly differed from the estimated ISI of some thromboplastins. Therefore, manufacturers should provide more accurate information about the ISI value of thromboplastins.

Estimation of Measurement Uncertainty of Factor Assays Using the Monte Carlo Simulation

OBJECTIVES

We aimed to quantify the measurement uncertainty (MU) for factor activities using the Monte Carlo simulation (MCS), which is a computational algorithm that simulates statistical sampling to obtain numerical results through complex mathematical calculations.

METHODS

The uncertainties of factor V (FV), factor VIII (FVIII), and factor X (FX) were simulated with two coagulation testing systems: ACL TOP 750 CTS (Instrumentation Laboratory) and STA Compact (Diagnostica Stago).

RESULTS

When the factor activities were 74% (FV), 68% (FVIII), and 89% (FX), the MUs were 3.5% (FV), 9.3% (VIII), and 2.8% (FX) for ACL TOP and 8.5% (FV), 18.2% (FVII), and 6.5% (FX) for STA Compact. MCS MUs were compared with MUs obtained from running actual samples (not simulated) using a method called the top-down approach. The MCS MU results were interchangeable with MUs from the top-down approach, except for FVIII from STA Compact.

CONCLUSIONS

The MCS procedure is well suited for the quantification of MUs for factor assays over the entire measurement range.

Verification of the ACL Top 50 Family (350, 550, and 750) for Harmonization of Routine Coagulation Assays in a Large Network of 60 Laboratories

OBJECTIVES

To verify a single platform of hemostasis instrumentation, the ACL TOP 50 Family, comprising 350, 550, and 750 instruments, across a large network of 60 laboratories.

METHODS

Comparative evaluations of instrument classes (350 vs 550 and 750) were performed using a large battery of test samples for routine coagulation tests, comprising prothrombin time/international normalized ratio, activated partial thromboplastin time (APTT), thrombin time, fibrinogen and D-dimer, and using HemosIL reagents. Comparisons were also made against existing equipment (Diagnostica Stago Satellite, Compact, and STA-R Evolution) and existing reagents to satisfy national accreditation standards. Verification of manufacturer normal reference ranges (NRRs) and generation of an APTT heparin therapeutic range were undertaken.

RESULTS

The three instrument types were verified as a single instrument class, which will permit standardization of methods and NRRs across all instruments (n = 75) to be deployed in 60 laboratories. In particular, ACL TOP 350 test result data were similar to ACL TOP 550 and 750 and showed no to limited bias. All manufacturer NRRs were verified with occasional minor variance.

CONCLUSIONS

This ACL TOP 50 Family (350, 550, and 750) verification will enable harmonization of routine coagulation across all laboratories in the largest public pathology network in Australia.

International Council for Standardization in Haematology (ICSH) laboratory guidance for the evaluation of haemostasis analyser-reagent test systems. Part 1: Instrument-specific issues and commonly used coagulation screening tests

Before a new method is used for clinical testing, it is essential that it is evaluated for suitability for its intended purpose. This document gives guidance for the performance of verification, validation and implementation processes required by regulatory and accreditation bodies. It covers the planning and execution of an evaluation of the commonly performed screening tests (prothrombin time, activated partial thromboplastin time, thrombin time and fibrinogen assay), and instrument-specific issues. Advice on selecting an appropriate haemostasis analyser, planning the evaluation, and assessing the reference, interval, precision, accuracy, and comparability of a haemostasis test system are also given. A second companion document will cover specialist haemostasis testing.