Immunosuppressive Drug Measurement by Liquid Chromatography Coupled to Tandem Mass Spectrometry: Interlaboratory Comparison in the Korean Clinical Laboratories

Background@#Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is increasingly used for immunosuppressive drug tests. However, most LC-MS/MS tests are laboratory-developed and their agreement is unknown in different Korean laboratories.This interlaboratory comparison study evaluated test reproducibility and identified potential error sources. @*Methods@#Test samples containing three concentrations of tacrolimus, sirolimus, everolimus, cyclosporine, and mycophenolic acid were prepared by pooling surplus samples from patients undergoing routine therapeutic drug monitoring and tested in duplicate in the participating 10 clinical laboratories. Reconstitution and storage experiments were conducted for the commonly used commercial calibrator set. The robust estimators of reproducibility parameters were calculated. Spearman’s rank correlation coefficient (rho, ρ) was used to evaluate the correlation between drugs. Multiple linear regression was used to determine whether the experimental conditions alter the calibration curves. @*Results@#The reproducibility coefficient of variation exceeded 10% only for sirolimus concentrations 1 and 2 (10.8% and 12.5%, respectively) and everolimus concentrations 1 and 2 (12.3% and 11.4%, respectively). The percent difference values showed weak correlations between sirolimus and everolimus (ρ = 0.334, P = 0.175). The everolimus calibration curve slope was significantly altered after reconstitution following prolonged 5°C storage (P = 0.015 for 14 days; P = 0.025 for 28 days); the expected differences at 6 ng/mL were 0.598% for 14 days and 0.384% for 28 days. @*Conclusions@#LC-MS/MS test reproducibility for immunosuppressive drugs seems to be good in the Korean clinical laboratories. Continuous efforts are required to achieve test standardization and harmonization, especially for sirolimus and everolimus.

Schemes and Performance Evaluation Criteria of Korean Association of External Quality Assessment (KEQAS) for Improving Laboratory Testing

External quality assessment (EQA) is important for evaluating clinical laboratories and enhancing their testing quality. EQA schemes are variable; thus, it is crucial that the EQA organizers share their experiences to continuously improve the EQA scheme. The Korean Association of External Quality Assessment Service (KEQAS) has been the leading, authorized EQA institute for the standardization and quality management of laboratory testing in Korean medical institutions since 1976. The EQA scheme underwent a major change in 2016, and the number of EQA programs increased significantly since then. The key changes implemented in EQA scheme include a fully computerized assessment to accelerate feedback and unification of the testing and reporting methods. We provide an overview of the EQA schemes and performance evaluation criteria of the KEQAS and suggest directions for achieving the global harmonization of EQA.

Establishment of Pediatric Reference Intervals for Routine Laboratory Tests in Korean Population: A Retrospective Multicenter Analysis

Background@#Reference intervals defined for adults or children of other ethnicities cannot be applied in the evaluation of Korean pediatric patients. Pediatric reference intervals are difficult to establish because children are in their growing stage and their physiology changes continuously. We aimed to establish reference intervals for routine laboratory tests for Korean pediatric patients through retrospective multicenter data analysis. @*Methods@#Preoperative laboratory test results from 1,031 pediatric patients aged 0 month–18 years who underwent minor surgeries in four university hospitals were collected. Age- and sex-specific reference intervals for routine laboratory tests were defined based on the Clinical and Laboratory Standards Institute (CLSI) EP28-A3c guidelines. @*Results@#The pediatric reference intervals determined in this study were different from existing adult reference intervals and pediatric reference intervals for other ethnicities. Most tests required age-specific partitioning, and some of those required sex-specific partitioning for at least one age-partitioned subgroup. Erythrocyte sedimentation rate, monocyte percentage, basophil percentage, activated partial thromboplastin time, glucose, cholesterol, albumin, bilirubin, chloride, and C-reactive protein did not show any difference between age- or sex-partitioned subgroups. @*Conclusions@#We determined Korean pediatric reference intervals for hematology, coagulation, and chemistry tests by indirect sampling based on medical record data from multiple institutions. These reference intervals would be valuable for clinical evaluations in the Korean pediatric population.

Standardization Status of Total Cholesterol Concentration Measurement: Analysis of Korean External Quality Assessment Data

Background@#Total cholesterol concentration measurement is important in the diagnosis of dyslipidemia and evaluation of cardiovascular disease risk factors. Measurement reliability for obtaining an accurate total cholesterol concentration requires procedure standardization. We evaluated the standardization status for total cholesterol concentration measurement through Korean external quality assessment (EQA) data analysis. @*Methods@#This study involved 1,670 laboratories that participated in the EQA of total cholesterol concentration measurements in 2019 for 32 products from different manufacturers. The target concentrations of three quality control (QC) materials (samples A, B, and C) were measured using the reference method and compared with EQA data. The performance criteria for total cholesterol concentration measurement were based on the National Cholesterol Education Program guidelines, with ± 3% inaccuracy. @*Results@#The target values and inaccuracies of the QC material based on the reference method measurements were 254.65 ± 7.64, 108.30 ± 3.25, and 256.29 ± 7.69 mg/dL (6.59 ± 0.20, 2.80 ± 0.08, and 6.63 ± 0.20 mmol/L) for samples A, B, and C, respectively.The performance criteria were not met in 42.7% laboratories for sample A, 68.4% of laboratories for sample B, and 38.0% laboratories for sample C. @*Conclusions@#Despite significant efforts to accurately measure total cholesterol concentrations, further actions are needed for measurement standardization. Manufacturers reporting values that differ from target values should check calibrator traceability; additional efforts to accurately measure total cholesterol concentrations are required for laboratories that use products from these manufacturers.

Recent Trends in Creatinine Assays in Korea: LongTerm Accuracy-Based Proficiency Testing Survey Data by the Korean Association of External Quality Assessment Service (2011–2019)

Background@#Accurate serum creatinine (Cr) concentration measurement is essential for evaluating kidney function. In 2011, the Korean Association of External Quality Assessment Service (KEQAS) launched an accuracy-based Cr proficiency testing (ABCr PT) survey. We analyzed long-term data of the KEQAS ABCr PT survey collected between 2011 and 2019 to assess recent trends in Cr assays in Korea. @*Methods@#The ABCr PT survey including three commutable fresh-frozen serum samples was performed twice a year. The target Cr concentration was assigned using isotope-dilution mass spectrometry. We analyzed data obtained from the participating laboratories, calculated the yearly bias, and evaluated bias trends for the major reagents and instruments. Outliers were excluded from all analysis. @*Results@#The mean percentage bias based on the total data of all participating laboratories was 10.8% in the 2011-A survey and 0.2% in 2019-B survey. Bias for the major reagents and instruments differed depending on the manufacturer. Enzymatic assays generally showed desirable bias ranging from –3.9% to 3.2% at all Cr concentrations and lower interlaboratory variability than non-enzymatic assays (enzymatic vs. non-enzymatic, 3.3%– 7.2% vs. 6.3%–9.1%). @*Conclusions@#Although the mean percentage bias of Cr assays tends to decrease over time, it is necessary to continuously strive to improve Cr assay accuracy, especially at low concentrations.

Development of an Operational Plan for the Liquid Biopsy External Quality Assessment Program in Korea

Background@#Liquid biopsy is a useful assay for the diagnosis, treatment, and prognosis prediction of solid tumors and its clinical application is expanding. Therefore, the need for developing an External Quality Assessment (EQA) protocol for liquid biopsy is increasing. In this study, we developed and implemented the liquid biopsy EQA program for the epidermal growth factor receptor mutation. @*Methods@#We validated the feasibility of the protocol using citrate instead of ethylenediaminetetraacetic acid (EDTA). Additionally, we analyzed the homogeneity and stability of the aliquoted quality control (QC) materials. Mutation-positive QC material with four mutations (exon 19 deletion, L858R, T790M, and exon 20 insertion) was used to make two types of QC materials (low and high) and the wild type material was used for the negative controls. If the EQA results showed consensus in more than 80% of the participating laboratories, the results were reported as acceptable or unacceptable. If not, we reported the results as not graded. @*Results@#Citrate showed equivalent performance to EDTA. Highly mutated QC material and mutation-negative QC material passed the homogeneity and stability test, but low-level mutant specimens showed inconsistent results. In total, 11 laboratories participated, and all of them reported consistent results except for low-grade mutant samples. Thus, the evaluation results were acceptable except for low mutation QC material. @*Conclusions@#The applicability of liquid biopsy is expanding. To obtain accurate test results, EQA is indispensable. Here, QC materials for liquid biopsy EQA were produced, distributed, and had its results analyzed. This study could be the foundation for further development of liquid biopsy EQA.

Identification of a Novel Splice Variant (c.423-8A>G) of APC by RNA Sequencing

No abstract available.

Performance Evaluation of the Stat Profile pHOx Ultra Blood Gas Analyzer

The objective of this study was to evaluate the analytical performance of the Stat Profile pHOx Ultra Blood Gas Analyzer (Nova Biomedical, USA), a new blood gas/chemistry analyser, including its precision and linearity, comparison studies, and the carry-over effect of commercial reagents and patient specimens. We assessed all the results on the basis of the Clinical and Laboratory Standards Institute guidelines. The following parameters were assessed: pH, partial pressure of carbon dioxide, partial pressure of oxygen, ionized calcium, ionized magnesium (iMg), and lactate concentration The total imprecision had a coefficient of variation of 0.0%–1.8%, and the linear measurement ranges for each parameter were all acceptable. In comparison with the Nova Critical Care Xpress Analyzer (Nova Biomedical, USA), the results indicated a good agreement, except for iMg. All carry-over ranges were between −0.5% and −1.4%. The Stat Profile pHOx Ultra Blood Gas Analyzer showed good analytical performance in terms of precision, linearity, comparison studies, and carry-over effect. The Stat Profile pHOx Ultra Blood Gas Analyzer can provide reliable measurements across a clinically relevant range and has potential use in laboratory tests.

A Questionnaire Survey on General Status and Opinions about Clinical Mass Spectrometric Analysis in Korea (2018)

The Clinical Mass Spectrometry Research Committee (CMSRC), in affiliation with the Korean Society of Clinical Chemistry (KSCC), conducted a questionnaire survey on opinions about the general status of clinical mass spectrometric analysis in Korea. As a result, we understand that this field has passed through the introductory stage and is settled as a field of clinical laboratory testing in Korea, with the number of new laboratories performing mass spectrometric analysis being low. In spite of the many difficulties in introducing and operating clinical mass spectrometric analysis, there is a strong interest in this field, and even though further expansion is expected, there are still many issues to be resolved. In the future, it will be necessary to make concrete and thorough efforts to further develop the laboratory tests using clinical mass spectrometric analysis in Korea, centering on the CMSRC affiliated with the KSCC.

Essential Elements for Establishing Clinical Next-generation Sequencing Testing

Over the past decade, next-generation sequencing (NGS) has evolved at an astonishing pace and has revolutionized clinical medicine as well as genomics research. The rapid advancements in NGS technologies have been accompanied by accumulating evidence of the analytical and clinical validity, and clinical utility of NGS. NGS is used worldwide. This review provides medical technicians and laboratory physicians with the essential elements for establishing clinical NGS testing. Here the authors briefly describe the advantages and drawbacks of currently available NGS platforms, potential sources of error in NGS workflow, and reference materials.

Plasma Neutrophil Gelatinase-Associated Lipocalin as a Marker of Tubular Damage in Diabetic Nephropathy

BACKGROUND: An increase in neutrophil gelatinase-associated lipocalin (NGAL) indicates tubular injury. Diabetic nephropathy causes typical changes in the kidney, characterized by glomerulosclerosis and eventual tubular damage. We validated the usefulness of plasma NGAL (pNGAL) as a biomarker of tubular damage in patients with diabetic nephropathy. METHODS: We included 376 patients with diabetes mellitus (260 patients with chronic renal insufficiency who had not received hemodialysis and 116 hemodialyzed due to diabetic nephropathy) and 24 healthy controls. Patients with chronic renal insufficiency were divided into three groups according to urinary albumin excretion (UAE) levels. pNGAL levels were measured using the Triage NGAL test (Alere, San Diego, CA, USA) and were compared between groups. We also examined whether pNGAL level was related to the degree of albuminuria and cystatin C-based glomerular filtration rate (GFR). RESULTS: Mean pNGAL levels of the healthy controls, chronic renal insufficiency patients with diabetes mellitus, and hemodialyzed patients were 61.9±5.3 ng/mL, 93.4±71.8 ng/mL, and 1,536.9±554.9 ng/mL, respectively. pNGAL level increased significantly in patients with severe albuminuria (P < 0.001) and had a moderate correlation with the degree of albuminuria (r=0.467; P < 0.001) and GFR (r=0.519; P < 0.001). Multivariate regression analysis showed that the pNGAL level was associated with tubular damage independent of patient age, sex, and GFR. CONCLUSIONS: pNGAL level independently reflects the degree of tubular damage in patients with diabetic nephropathy. Measurement of pNGAL, combined with UAE, would enable simultaneous, highly reliable assessments of tubular damage for such patients.

Report on the External Quality Assessment Scheme of Hepatitis Viral Markers in Korea, (2016–2017)

As part of the immunoserology program of the Korean Association of External Quality Assessment Service, we organized two trials on the external quality assessment of hepatitis viral markers in 2016 and 2017. The hepatitis viral antigens and antibodies program consisted of 10 test items. We delivered two and three types of pooled sera specimens to 965 and 965 institutions for the first and second trials of external proficiency testing in 2016, respectively. The number of participating laboratories was 915 (94.8%) and 913 (95.0%) in the first and second trials in 2016, respectively. We also delivered three kinds of pooled sera specimens to 936 and 1,015 institutions for the first and second trials of external proficiency testing in 2017, respectively. The number of participating laboratories was 920 (98.3%) and 996 (98.1%) in the first and second trials in 2017, respectively. The most commonly tested items were hepatitis B surface antigen, followed by the antibodies to hepatitis B surface antigen, anti-hepatitis C virus, hepatitis B envelope antigen, antibodies to hepatitis B envelope antigen, anti-hepatitis A virus and antibodies to hepatitis B core antigen. The most frequently used methods for detecting viral markers were the chemiluminescence immunoassay and the electrochemiluminescence immunoassay, but they yielded a few-false positive results due to the matrix effect. The immunochromatographic assay yielded false-negative results for anti-hepatitis A virus due to low sensitivity. Continuous improvement in the quality of viral hepatitis testing through participation in the survey seems necessary.

Evaluation of the 1B Equation to Estimate Glomerular Filtration Rate in Pediatric Patients with Cancer

The 1B equation is recommended for calculating the glomerular filtration rate (GFR) in children. Since few reports have evaluated the performance of the 1B equation, we investigated the performance of estimated GFR (eGFR) equations with the blood urea nitrogen (BUN) variable for pediatric cancer patients. In total, 203 children with cancer who underwent measured GFR (mGFR) assessment were enrolled. The median (range) mGFR and eGFR calculated using the updated Schwartz equation were 118 (43–241) and 135 (34–257) mL/min/1.73 m², respectively. The bias, precision (root mean square error [RMSE]), and accuracy (P30, mGFR±30%) of three eGFR equations including updated Schwartz, 1B, and full age spectrum (FAS) were compared. The median bias (mL/min/1.73 m²) was: updated Schwartz, 8.5; 1B, −9.0; and FAS, 4.2. The biases for all three eGFR equations were significantly different from zero. The P30 was: updated Schwartz, 63.5%; 1B, 66.0%; and FAS, 66.0%. The RMSE was the lowest for the 1B equation (40.4), followed by FAS (42.3), and updated Schwartz (45.5). The median eGFR/mGFR ratio for the eGFR equations decreased with age and reduced kidney functions (i.e., increased creatinine and BUN concentrations). The bias may be further reduced by using the average from two equations, such as the updated Schwartz and 1B, or FAS equation, rather than using the updated Schwartz or 1B equation alone. The use of the 1B equation may underestimate the GFR. Using creatinine and BUN variables in the eGFR equation may yield a more accurate estimate of the GFR in pediatric cancer patients.

Multi-center Performance Evaluations of Tacrolimus and Cyclosporine Electrochemiluminescence Immunoassays in the Asia-Pacific Region

BACKGROUND: The immunosuppressant drugs (ISDs), tacrolimus and cyclosporine, are vital for solid organ transplant patients to prevent rejection. However, toxicity is a concern, and absorption is highly variable across patients; therefore, ISD levels need to be precisely monitored. In the Asia-Pacific (APAC) region, tacrolimus and cyclosporine concentrations are typically measured using immunoassays. The objective of this study was to assess the analytical performance of Roche Elecsystacrolimus and cyclosporinee electrochemiluminescence immunoassays (ECLIAs). METHODS: This evaluation was performed in seven centers across China, South Korea, and Malaysia. Imprecision (repeatability and reproducibility), assay accuracy, and lot-to-lot reagent variability were tested. The Elecsys ECLIAs were compared with commercially available immunoassays (Architect, Dimension, and Viva-E systems) using whole blood samples from patients with various transplant types (kidney, liver, heart, and bone marrow). RESULTS: Coefficients of variation for repeatability and reproducibility were ≤5.4% and ≤12.4%, respectively, for the tacrolimus ECLIA, and ≤5.1% and ≤7.3%, respectively, for the cyclosporine ECLIA. Method comparisons of the tacrolimus ECLIA with Architect, Dimension, and Viva-E systems yielded slope values of 1.01, 1.14, and 0.897, respectively. The cyclosporine ECLIA showed even closer agreements with the Architect, Dimension, and Viva-E systems (slope values of 1.04, 1.04, and 1.09, respectively). No major differences were observed among the different transplant types. CONCLUSIONS: The tacrolimus and cyclosporine ECLIAs demonstrated excellent precision and close agreement with other immunoassays tested. These results show that both assays are suitable for ISD monitoring in an APAC population across a range of different transplant types.

Reducing the Reporting Time by Improving Laboratory Processing for Inpatient Routine Chemistry Tests

BACKGROUND: The returning time of inpatient specimen analysis is usually slow because phlebotomists deliver all the collected specimens at the end of their work cycle. In addition, manual specimen reception further delays the reporting time and imposes a heavy workload on the technical staff, thus compromising effectiveness. Therefore, we have created an automated specimen reception system to tackle testing delays and enhance the efficiency and quality of specimen collection and handling. METHODS: In May 2015, the pre-analytical processing of inpatient samples was renovated. We automated the specimen reception in parallel with barcode printing and introduced pneumatic tubes to deliver samples for routine chemistry tests. We compared the reporting time of the automated system with that of the manual system and analyzed the distribution pattern of the specimens according to handling time. RESULTS: The median reporting time was advanced by 41 minutes, from 09:33 AM to 08:52 AM for the manual and automated reception, respectively. Moreover, with the reduction in hands-on time, the blood specimens reached the laboratory immediately after phlebotomy, thereby improving the processing efficiency by spreading out the interval during which the specimens arrived in the laboratory. Additionally, the new system allowed the identification of the phlebotomist who collected the specimens and tracking the specimens from collection to test result. CONCLUSIONS: With the introduction of our automatic reception system, the reporting time was considerably reduced. Therefore, the satisfaction of the clinician and the technical staff was improved.

Performance Evaluation of ADVIA Centaur XPT

We have evaluated the performance of a recently developed immunoassay analyzer, ADVIA Centaur XPT (Siemens, Germany). Precision, linearity, and comparison studies were performed according to the CLSI guidelines. The test items evaluated were ferritin, folate, human epidermal growth factor receptor 2/neu, homocysteine, vitamin B₁₂, B-type natriuretic peptide, creatine kinase–myocardial band, myoglobin, procalcitonin, troponin I. Bio-Rad control materials, linearity materials, and patients' samples were used for the evaluation. For the correlation study, ADVIA Centaur XP (Siemens) were used as comparative methods. The total coefficients of variations (CVs) of the analytes were between 2.5% and 7.0%. The results of linearity evaluation were also acceptable for the range tested. Correlations with comparative methods were good. The overall analytical performance of ADVIA Centaur XPT is acceptable for the immunology analyzer. Therefore, ADVIA Centaur XPT is expected to be widely used.

Accuracy Assessment of Five Equations Used for Estimating the Glomerular Filtration Rate in Korean Adults

BACKGROUND: We aimed to assess the performance of the five creatinine-based equations commonly used for estimates of the glomerular filtration rate (eGFR), namely, the creatinine-based Chronic Kidney Disease Epidemiology Collaboration (CKD-EPIcr), Asian CKD-EPI, revised Lund–Malmö (revised LM), full age spectrum (FAS), and Korean FAS equations, in the Korean population. METHODS: A total of 1,312 patients, aged 20 yr and above who underwent ⁵¹Cr-EDTA GFR measurements (mGFR), were enrolled. The bias (eGFR–mGFR) and precision (root mean square error [RMSE]) were calculated. The accuracy (P30) of four eGFR equations was compared to that of the CKD-EPIcr equation. P30 was defined as the percentage of patients whose eGFR was within±30% of the mGFR. RESULTS: The mean bias (mL·min⁻¹·1.73 m⁻²) of the five eGFR equation was as follows: CKD-EPIcr, -0.6; Asian CKD-EPI, 2.7; revised LM, -6.5; FAS, -2.5; and Korean FAS, -0.2. The bias of the Asian CKD-EPI, revised LM, and FAS equations showed a significant difference from zero (P<0.001). The RMSE values were as follows: CKD-EPIcr, 15.6; Asian CKD-EPI, 15.6; revised LM, 17.9; FAS, 16.3; and Korean FAS, 15.8. There were no significant differences in the P30 except for the Asian CKD-EPI equation: CKD-EPIcr, 76.6%; Asian CKD-EPI, 74.7%; revised LM, 75.8%; FAS, 76.0%; and Korean FAS, 75.8%. CONCLUSIONS: The CKD-EPIcr and Korean FAS equations showed equivalent analytical and clinical performances in the Korean adult population.

Annual Report on the External Quality Assessment Scheme for Routine Clinical Chemistry in Korea (2016)

In 2016, the clinical chemistry proficiency-testing program consisted of 21 programs, including the general chemistry program of the Korean Association of External Quality Assessment Service. The general chemistry program consisted of 28 test items and was conducted using two level control materials four times per year. Based on the information and results for each test item entered by each institution, statistical analysis data according to test method, instrument, and reagent were reported. The report comprised a general statistics report showing the characteristics of all participating institutions and a separate institutional report showing the evaluation data of individual institutions. The statistics included the number of participating institutions and the mean, standard deviation, coefficient of variation, median, minimum, and maximum values for each group. Each report was composed of a table, histogram, and Levey-Jennings chart showing the statistics for each test item. The results of each institution and the statistics for each classification are presented in the table showing the statistics, and a standard deviation index is presented together with a method classification and a classification by reagent companies. A total of 14 items, including albumin, were evaluated by more than 1,000 institutions. There was no significant difference in the distribution of the measurement methods compared with those used in the previous year. The coefficient of variation showed a tendency to increase as the concentration of the level control material decreased and as the number of participating institutions decreased for each test item. Most of them showed a coefficient of variation within 10%. These statistical data will be useful when interpreting the survey results from the institutions and selecting a test method.

Clinical Pharmacogenetic Testing and Application: Laboratory Medicine Clinical Practice Guidelines

Pharmacogenetic testing for clinical applications is steadily increasing. Correct and adequate use of pharmacogenetic tests is important to reduce unnecessary medical costs and adverse patient outcomes. This document contains recommended pharmacogenetic testing guidelines for clinical application, interpretation, and result reporting through a literature review and evidence-based expert opinions for the clinical pharmacogenetic testing covered by public medical insurance in Korea. This document aims to improve the utility of pharmacogenetic testing in routine clinical settings.

Annual Report on the External Quality Assessment of Therapeutic Drug Monitoring and Testing for Drugs of Abuse in Korea (2015)

As an annual function of the Therapeutic Drug Monitoring Subcommittee of Korean Association of External Quality Assessment Service (K-EQAS), we organised two trials for an external quality assessment of therapeutic drug monitoring (TDM) and testing for drugs of abuse (DOA) in 2015. For the TDM assessment, we sent low- and high-level control materials from various clinical institutions, and for the DOA testing, we sent positive and negative control materials. The number of participating laboratories was 105 for the TDM trial and 106 for the DOA test. The average number of drug items provided was 5.6 per institution. The most commonly tested substances, in descending order, were: valproic acid, digoxin, vancomycin, tacrolimus, and carbamazepine. The mean inter-laboratory coefficients of variation for low- and high-level TDM control materials were 7.3% and 7.4%, respectively. The most widely used TDM analysers were the Architect i System (Abbott Diagnostics, USA), followed by the Cobas Integra (Roche Diagnostics, Switzerland) and the Cobas c501 analyser (Roche Diagnostics). The number of participating laboratories for the DOA analysis was 16% higher that than of our 2014 study. In 98.6% of cases, our analysis confirmed the reliabilityviability of the tests at participating DOA laboratories in both trials. In the external quality assessment of TDM by the TDM subcommittee of K-EQAS in 2015, the overall performance of TDM testing was found to be similar to that reported in previous years, and inter-laboratory precision was higher than that of 2014. Continuous improvement in the quality of TDM testing through participation in a proficiency-testing program will remain necessary in the future.