Comparative Analysis of Seven Equations for Estimated Glomerular Filtration Rate and Their Impact on Chronic Kidney Disease Categorization in Korean Patients at Local Clinics and Hospitals.

(1) Background: Accurate estimation of the glomerular filtration rate (eGFR) is essential for the early detection of chronic kidney disease (CKD), targeted interventions, and ongoing monitoring. Although various equations for calculating eGFR exist, comparative studies on eGFR levels and the impact of these equations on CKD prevalence are limited in the Korean population. (2) Methods: We compared eGFR levels calculated using seven equations and investigated the prevalence of CKD through a retrospective analysis of the data from Korean adult patients who visited local clinics and hospitals and underwent simultaneous serum creatinine (Cr) and cystatin C (Cys-C) measurements. The equations analyzed were: 2006 MDRD, 2009 CKD-EPI Cr, 2012 CKD-EPI Cys-C, 2012 CKD-EPI Cr & Cys-C, 2021 CKD-EPI Cr, 2021 CKD-EPI Cr & Cys-C, and 2021 EKFC. (3) Results: This study included 6688 Korean patients (3736 men and 2952 women; median age: 61.4; IQR: 47.2-73.4). Among the equations, the median eGFR levels were the highest when using the 2021 CKD-EPI Cr & Cys-C equation (85.1 mL/min/1.73 m2) and the lowest when using the 2006 MDRD equation (73.4 mL/min/1.73 m2). The highest prevalence of decreased eGFR < 60 mL/min/1.73 m2 (equivalent to or worse than G3a CKD) was noted with the 2012 CKD-EPI Cys-C equation (32.4%), while the lowest was with the 2021 CKD-EPI Cr equation (22.9%), resulting in a maximum prevalence difference of 9.5%. (4) Conclusions: The prevalence of CKD varies based on the eGFR equation used and the patient's age. Equations that include Cys-C may identify a larger number of patients with decreased kidney function.

Effect of Adding Apolipoprotein B Testing on the Prevalence of Dyslipidemia and Risk of Cardiovascular Disease in the Korean Adult Population.

Traditional lipid parameters-including total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and non-HDL-C (calculated as TC minus HDL-C)-have long been used as indicators of cardiovascular disease (CVD) risk. The laboratory records of 9604 Korean adults who underwent traditional lipid panel tests (TC, TG, and HDL), as well as ApoB testing, were analyzed to evaluate the prevalence of dyslipidemia and high CVD risk (utilizing the NCEP ATP III criteria for traditional lipid panels and various ApoB test cutoffs recommended by international guidelines (145 mg/dL, 130 mg/dL, and 100 mg/dL)). The overall prevalence of dyslipidemia, as determined by traditional lipid panel criteria, was 27.4%. Utilizing the ApoB cutoffs of 145 mg/dL, 130 mg/dL, and 100 mg/dL resulted in prevalence figures of 5.3%, 11.0%, and 36.3%, respectively. The concordance in dyslipidemia classification between traditional lipid tests and ApoB at cutoffs of 145 mg/dL, 130 mg/dL, and 100 mg/dL was 78.4%, 81.3%, and 74.7%, respectively. Up to 17.5% of participants, based on an ApoB cutoff of ≥100 mg/dL, exhibited isolated high ApoB in the absence of traditional lipid test anomalies. Incorporating ApoB testing could enhance the identification of Koreans at high CVD risk.

Exploring Utilization and Establishing Reference Intervals for the Apolipoprotein B Test in the Korean Population.

We investigated the reference intervals for Apolipoprotein B (ApoB), a valuable biomarker for cardiovascular diseases, in Korean adults who had undergone health check-ups and showed normal lipid levels under traditional lipid tests, including total cholesterol, triglyceride, and high-density lipoprotein cholesterol, along with ApoB. We compared the findings with different cutoffs for ApoB from international clinical guidelines. Among a total of 264,105 traditional lipid test sets, only 464 (0.2%) included ApoB tests, indicating underutilization of this test in health check-up clinics in Korea. From these 464 samples, 334 ApoB results (164 men and 170 women) with normal traditional lipid test results were used to establish reference intervals. Using the parametric method (mean ± 2 SD), the reference intervals ranged from 46 to 134 mg/dL for men and 49 to 129 mg/dL for women. Employing the non-parametric method (central 95th percentile value), the reference intervals ranged from 50 to 131 mg/dL for men and 51 to 127 mg/dL for women. The prevalence of high ApoB did not significantly differ by sex when considering the established reference intervals for each sex and the cutoffs recommended by international clinical guidelines. This study enhances knowledge on ApoB reference intervals in the Korean population, and it will in aid test result interpretation for clinicians and laboratories.

Investigation of the Prevalence of Diminished Ovarian Reserve in Korean Women of Reproductive Age.

Diminished ovarian reserve can be assessed biochemically using serum anti-Müllerian hormone (AMH) and follicle-stimulating hormone (FSH) tests. This study aimed to evaluate the prevalence of diminished ovarian reserve in a large population of reproductive-aged women by age and geographic region in Korea using different cutoffs of serum AMH and FSH levels. In 2022, 13,351 women underwent both AMH and FSH tests. The prevalence of diminished ovarian reserve increased markedly with age. Although cutoffs for AMH and FSH levels are different in USA and Korean guidelines, the overall prevalence of diminished ovarian reserve was comparable. The maximum prevalence was 3.8%, 6.0%, 11.0%, 28.6%, 69.3%, and 95.0% in women aged 20-24, 25-29, 30-34, 35-39, 40-44, and 45-49 years, respectively. The overall prevalence and age-adjusted prevalence of diminished ovarian reserve were 37.2% and 38.4%, respectively. Women who had only increased serum FSH without decreased AMH represented 1.1% (by Korean guidelines) and 2.5% (by USA guidelines) of all women. Serum AMH and FSH tests were underutilized on Jeju Island. The results of this study provide basic knowledge about diminished ovarian reserve for use in infertility support programs and the field of maternal aging.

The Utilization of Serum Folate and Homocysteine Tests and the Prevalence of Folate Deficiency in Reproductive-Age Korean Women during the COVID-19 Pandemic.

We investigated the prevalence of folate deficiency and associated factors in a large population of Korean women of reproductive age during the COVID-19 pandemic. We utilized different cut-offs and evaluated age, year of testing, geographical region, and the utilization of serum homocysteine levels. Out of the 27,758 women evaluated, the overall prevalence of folate deficiency was 12.5% (<4 ng/mL, metabolic indicator) and 5.4% (<3 ng/mL, hematologic indicator). Homocysteine testing was observed in 8.4% of women, with 2.7% having elevated homocysteine levels (>15.4 µmol/L). According to our multiple logistic regression analysis, younger women, particularly those aged 20 to 24 years, tested in 2020, and from Jeolla province, Gyeongsang province, and Jeju Island, were identified as being more prone to folate deficiency. Receiver operating characteristic curve analysis demonstrated that a cut-off of >8.4 µmol/L provided the most accurate definition of folate deficiency with serum folate levels <4 ng/mL, while a cut-off of >8.8 µmol/L best defined folate deficiency with serum folate levels <3 ng/mL, with both cut-offs being lower than 15.4 µmol/L. Our study emphasizes the prevalence of folate deficiency, associated factors, and the role of homocysteine in planning nutritional support programs in Korea.

Lipid distributions in the Global Diagnostics Network across five continents.

AIMS: Lipids are central in the development of cardiovascular disease, and the present study aimed to characterize variation in lipid profiles across different countries to improve understanding of cardiovascular risk and opportunities for risk-reducing interventions. METHODS AND RESULTS: This first collaborative report of the Global Diagnostics Network (GDN) evaluated lipid distributions from nine laboratory organizations providing clinical laboratory testing in 17 countries on five continents. This cross-sectional study assessed aggregated lipid results from patients aged 20-89 years, tested at GDN laboratories, from 2018 through 2020. In addition to mean levels, the World Health Organization total cholesterol risk target (<5.00 mmol/L, <193 mg/dL) and proportions in guideline-based low-density lipoprotein cholesterol (LDL-C) categories were assessed. This study of 461 888 753 lipid results found wide variation by country/region, sex, and age. In most countries, total cholesterol and LDL-C peaked at 50-59 years in females and 40-49 years in males. Sex- and age-group adjusted mean total cholesterol levels ranged from 4.58 mmol/L (177.1 mg/dL) in the Republic of Korea to 5.40 mmol/L (208.8 mg/dL) in Austria. Mean total cholesterol levels exceeded the World Health Organization target in Japan, Australia, North Macedonia, Switzerland, Germany, Slovakia, and Austria. Considering LDL-C categories, North Macedonia had the highest proportions of LDL-C results >4.91 mmol/L (>190 mg/dL) for both females (9.9%) and males (8.7%). LDL-C levels <1.55 mmol/L (<60 mg/dL) were most common among females in Canada (10.7%) and males in the UK (17.3%). CONCLUSION: With nearly a half billion lipid results, this study sheds light on the worldwide variability in lipid levels, which may reflect inter-country differences in genetics, lipid testing, lifestyle habits, and pharmacologic treatment. Despite variability, elevated atherogenic lipid levels are a common global problem, and these results can help inform national policies and health system approaches to mitigate lipid-mediated risk of cardiovascular disease.

Development and Validation of Multiple Equations for Low-Density Lipoprotein and Apolipoprotein B in Korean Patients Visiting Local Clinics and Hospitals.

We investigated the utilization of apolipoprotein B (ApoB), an independent risk factor for cardiovascular disease, and developed and validated a translational equation for calculating low-density lipoprotein cholesterol (LDL-C) in the Korean population visiting local clinics and hospitals. Among a total of 469,520 data sets of the lipid profile panel (total cholesterol, triglycerides, and high-density lipoprotein cholesterols), 142,932 lipid test sets with data on LDL-C and/or ApoB were used for statistical analysis. Using linear regression analysis, we created ApoB percentile value-derived LDL-C equations in a creating set and validated them with previously reported equations (a total of 11 equations) in comparison to directly measured LDL-C using two independent validating sets. Among all lipid test sets, the simultaneously measured ApoB test only accounted for 2.0%, indicating its underutilization in Korea. The ApoB-derived equations, which were derived in this study and previous studies, showed an overall agreement of ≥94.3% for NCEP ATP III criteria. However, the accuracy of the equations varied among data sets of populations. Future studies are needed to validate translational equations for ApoB and LDL-C in different populations to clarify the clinical implications of these equations.

Utilization of Glucose-6-Phosphate Dehydrogenase Test and the Prevalence of Enzyme Deficiency in Korea.

Glucose-5-phosphate dehydrogenase (G6PD) deficiency is an X-linked genetic disorder that affects red blood cells' metabolism. This retrospective study aimed to investigate the prevalence and characteristics of G6PD testing in Korea. Data were collected from laboratory information systems between July 2021 and June 2022. A total of 5193 patients (1722 males and 3471 females) with a median age of 55.1 years (interquartile range, IQR 44.6 to 64.5) were tested for whole blood G6PD, with 1.6% of tests performed on patients of non-Korean ethnicity. The majority of tests were performed in hospitals (37.7%) or local clinics (34.5%). Interestingly, no female children were tested for whole blood G6PD during the study period. The prevalence of decreased G6PD activity (<7.9 U/g Hb) was 0.4% (19/5111 Koreans and 2/82 non-Koreans), and only seven male patients with G6PD deficiency (<30% of the male median) were identified, with ages ranging from 4.8 months to 50.2 years. No female patients with G6PD deficiency were found. Further research is necessary to determine the clinical significance of G6PD test results and monitor their use.

Prevalence of Iron Deficiency Anemia Indicated for Intravenous Iron Treatment in the Korean Population.

We aimed to investigate the number and prevalence of patients indicated for intravenous iron treatment in a large Korean population using criteria based on laboratory test results in an effort to extract indirect information on the need for intravenous iron treatment. Between 1 January 2019 and 31 December 2021, a total of 83,994 Korean patients (30,499 men and 53,495 women) with a median age of 46 years (interquartile range, 30-61) were evaluated using iron deficiency anemia-associated laboratory tests and serum creatinine tests of estimated glomerular filtration rates. The overall prevalence of anemia (Hb ≤ 11 g/dL) was 16.5%, and the proportion of patients with possible chronic kidney disease who had an estimated glomerular filtration rate < 60 mL/min/1.73 m2 was 11.4%. The number of patients indicated for reimbursable intravenous iron treatment was higher in women than in men, higher in older patients, and higher in 2021 than in 2019 (all p < 0.001). The prevalence of patients indicated for reimbursable intravenous iron treatment was up to 30.0% in those ≥ 80 years of age in 2019. The results of this study provide basic knowledge about the use of iron deficiency anemia-associated laboratory tests in planning nutritional support programs using an intravenous iron formulation in Korea.

Understanding the Utilization of the Krebs von den Lungen 6 Test in a Clinical Laboratory.

BACKGROUND: We aimed to investigate Krebs von den Lungen 6 (KL-6) assay results in a clinical laboratory to better understand patient population and test utilization. METHODS: We investigated serum KL-6 test results in Korean adults by the type of medical institution visited between October 2019 and December 2021. RESULTS: Overall, 7,677 KL-6 tests were performed in 5,527 Korean adults (3,627 men and 1,900 women) with a median age of 68.3 years (interquartile range 59.6 - 75.8). The median KL-6 level in 507 patients who visited health promotion centers was lower than the other 5,020 patients who visited other types of medical institutions (196 U/mL vs. 588.0 U/mL, respectively, p < 0.05). Increased KL-6 levels (≥ 500 U/mL) were observed in 0.8% of patients who visited health promotion centers and in 57.1% of patients who visited other types of medical institutions. CONCLUSIONS: This study will help to understand patient populations and test utilization for KL-6 in clinical laboratories in Korea.

Understanding Utilization and Seroprevalence of Syphilis Tests in Local Clinics and Hospitals in Korea.

BACKGROUND: Diagnosis of syphilis, a sexually transmitted infection, can be based on clinical information and various combinations of results of both non-treponemal and treponemal assays. Because understanding a patient population is helpful for test utilization in the clinical laboratory, we aimed to investigate the results of syphilis serology tests requested from local clinics in Korea. METHODS: We retrospectively evaluated the syphilis serology test results of serum Rapid Plasma Reagin (RPR), Treponema pallidum latex agglutination (TPLA), RPR titer, and fluorescent treponemal antibody absorption (FTA-ABS) IgG, and IgM tests performed in Korean adults in the laboratory information system of Green Cross Laboratories. We investigated the patterns of syphilis serology test results and possible interpretation according to combinations of syphilis serology based on a traditional testing algorithm. RESULTS: During the one-year study period, 33,746 RPR tests were performed in Korean adults (7,622 men and 26,124 women) with a median age of 35.1 years (interquartile range 30.8 - 43.4 years). Among these RPR tests, 317 (0.9%) showed RPR+ results and were performed simultaneous with TPLA tests. Among these 317 patients, 187 (59.0%) had RPR+/TPLA+ results. Among 130 patients with RPR+/TPLA- results, FTA-ABS IgG and IgM were only tested in 15 (11.5%): 14 were IgG-/IgM-, and one who underwent only the IgM test showed a negative result (probably a biological false positive of RPR). Among 187 RPR+/TPLA+ patients, 60 (2.1%) had RPR titer ≥ 1:8, and 10 were FTA-ABS IgM+ (including weak reactive results probably due to current infection or rare biological false-positive). Among 121 patients with RPR+/TPLA+/RPR titer ≤ 1:4, 30 were tested for FTA-ABS IgG and/or IgM: the two FTA-ABS IgM+ (including weak reactive) patients had an RPR titer of 1:4. CONCLUSIONS: This study will help to understand patient populations and test utilization for syphilis serology test interpretation in clinical laboratories in Korea. Further studies are needed to investigate the clinical impact of test utilization of syphilis serology in Korea.

Seroprevalence of Anti-Thyroglobulin Antibodies in Korea.

BACKGROUND: The appropriate use of the thyroglobulin (Tg) test involves the concurrent measurement of Tg auto-antibodies (Tg Ab) due to the potential for false low or false high Tg due to Tg Ab interference. METHODS: We retrospectively reviewed Tg and Tg Ab test results requested from local clinics and hospitals in Korea between July 1, 2020 and June 30, 2021. RESULTS: During the study period, 13,811 Tg tests were performed. Among them, 6,769 Tg tests were identified as being repeatedly measured from 2,988 Korean adults. Among the 6,769 performed Tg tests, 2,733 (40.4%) did not have concurrently performed Tg Ab tests. Among the 2,988 subjects, 1,089 (36.4%) had no concurrently measured Tg Ab test results. Among 4,036 Tg results with concurrently measured Tg Ab, 1,045 (25.9%) had positive Tg Ab results, which could interfere with Tg concentration measurements. CONCLUSIONS: The Tg Ab test appears to be underutilized in Korea.

Intra-Individual Changes in Total Procollagen-Type 1 N-terminal Propeptide in a Korean Adult Population.

We aimed to investigate intra-individual changes in total procollagen-type 1 N-terminal pro-peptide (P1NP), a biochemical marker of bone turnover, to understand patient populations and test utilization in a Korean adult population while considering different definitions of least significant changes by sex, age, and medical institution type. Overall, 31,501 P1NP tests were performed on 24,644 Korean adults (3389 men and 21,255 women) with a median age of 68.9 years (interquartile range, IQR, 61.2-77.2) for osteoporosis evaluation. Among these, 1331 (5.4%) patients (127 men and 1204 women) underwent ≥3 follow-up P1NP measurements. The median follow-up period was 12.5 months (IQR, 11.7-15.9). Among 1331 patients, 64.4% experienced a decrease in P1NP and 35.6% experienced an increase in P1NP during follow-up. Among these, the proportion of patients who experienced serum P1NP changes ≥14.4% from baseline was 92.3%, and the proportion of patients who achieved ≤40 ng/mL (a median level of premenopausal Korean women) during follow-up was 31.8%. The overall proportion of patients that experienced a serum P1NP change exceeding the least significant change during follow-up was not significantly different by the type of medical institution.

Alterations in Glomerular Filtration Rates Using Different Algorithms in the Korean Population Visiting Local Clinics and Hospitals.

We retrospectively reviewed the estimated glomerular filtration rates (eGFR) calculated by three equations: (1) Modification of Diet in Renal Disease Study (MDRD), (2) Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) using serum creatinine in 2009 (CKD-EPI 2009), and (3) CKD-EPI suggested in 2021 (CKD-EPI 2021), in an adult Korean population visiting local clinics and hospitals for health check-ups between 2019 and 2021 to investigate the effect of changes in the prevalence of chronic kidney diseases using those equations. During the study period, serum creatinine tests were performed on 442,566 subjects (205,236 men and 237,330 women). The overall prevalence rates of decreased eGFR (<60 mL/min/1.73 m2) at baseline measurement were as follows: 3.4% using MDRD, 2.8% using CKD-EPI 2009, and 2.1% using CKD-EPI 2021. The prevalence of decreased eGFR increased with age. Among 442,566 tests, specimens having simultaneously measured random urine dipstick tests for proteinuria represented 6.0% of the population, and the albumin-creatinine ratio (ACR) was 0.3%. The prevalence of specimens having both decreased eGFR and proteinuria was significantly different among equations (p < 0.05). Among the three equations, MDRD and CKD-EPI 2009 had a similar specimen prevalence of decreased eGFR and proteinuria (≥1+) using a dipstick test or albuminuria (urine ACR > 30 mg/g creatinine), while those based on CKD-EPI 2021 were about half of those based on MDRD and CKD-EPI 2009. Future studies are needed to clarify the clinical impact of the changes in the calculations for eGFR.

Method Performance Verification of Anti-GAD65 and Anti-Insulin antibody Assays.

BACKGROUND: The aim of this study was to evaluate the performance of chemiluminescence immunoassays for anti-GAD65 and anti-insulin antibodies following user verification guidelines. METHODS: The analytical performance of anti-GAD65 and anti-insulin antibodies using a MAGLUMI 2000 analyzer was verified following user verification guidelines by the Clinical and Laboratory Standards Institute. RESULTS: Performance specifications including precision, linearity, carry-over, cutoffs for positive results, reference intervals, and comparability with pre-existing commercially available radioimmunoassays using patient specimens and certified reference material were verified (coefficients of variation for precision of anti-GAD65 and anti-insulin antibodies were 2.6% and 3.4%, respectively). Comparability assessed using clinical serum specimens showed overall agreement with radioimmunoassay of 87.2% (95% confidence interval 74.8% - 94.0%) for the anti-GAD65 antibody assay and 85.4% (95% confidence interval 71.6% - 93.1%) for the anti-insulin antibody assay. CONCLUSIONS: The results of this study verified the analytical performance of MAGLUMI anti-GAD65 and anti-insulin antibody assays for clinical use.

Utilization of Small Dense Low-Density Lipoprotein Cholesterol Testing in Korean Patients Visiting Local Clinics and Hospitals.

Small dense low-density cholesterol (sdLDL) has been the focus of studies due to its potential as an independent risk factor for atherosclerotic cardiovascular diseases. We aimed to investigate the utilization of sdLDL testing by LDL particle size analysis and the prevalence of an sdLDL predominant phenotype in Korean adult patients by visiting local clinics and hospitals. Among 9222 Korean adults (4577 men and 4645 women) with a median age of 62.8 years (interquartile range, IQR 54.5 to 71.8 years) undergoing lipid profile testing using LDL particle size analysis, the prevalence of hypercholesterolemia (total cholesterol ≥ 240 mg/dL), hypo HDL cholesterolemia (<40 mg/dL), and hyper LDL cholesterolemia (≥160 mg/dL) was 7.8%, 12.9%, and 0.5%, respectively. The overall prevalence of the sdLDL predominant non-A phenotype of LDL was 46.8% of study subjects. Approximately 32.8% of the study subjects possessed lipid test results that did not exhibit increased risk except for sdLDL (only the sdLDL predominant non-A phenotype as a risk factor). In Korea, sdLDL testing was utilized in patients whose LDL cholesterol level was not increased. Future studies to clarify the clinical significance of this test in the Korean population are needed.

Lipoprotein(a) in the Korean Pediatric Population Visiting Local Clinics and Hospitals.

In this paper we investigate serum lipoprotein(a), an independent risk factor for cardiovascular disease in the Korean pediatric population. Visiting local clinics and hospitals, 600 lipoprotein(a) tests were performed on 416 Korean children and adolescents (124 boys and 292 girls), with a median age of 11.1 years (interquartile range, IQR, 9.8-13.9). The median lipoprotein(a) level was 21.5 nmol/L (IQR, 8.2-51.7). Among the 416 patients, the 90th percentile value of the initial lipoprotein(a) measurement was 107.8 nmol/L. The proportion of patients with lipoprotein(a) ≥ 100 nmol/L was 11.3%. The lipoprotein(a) level and the proportion of patients with lipoprotein(a) ≥ 100 nmol/L were not significantly different among sex, or age group. Among the 416 patients, 122 (29.3%, 21 boys and 101 girls) underwent at least two follow-up lipoprotein(a) measurements. The median follow-up period was 6.7 months (IQR, 5.5-11.8). The median lipoprotein(a) level across the 122 patients was 25 nmol/L (IQR 10.0-72.0). Among those patients, seven (5.7%) experienced an increase in serum lipoprotein(a) to ≥100 nmol/L during follow-up measurements. Further studies are needed in the Korean pediatric population in order to clarify the clinical significance of this change long-term.

Patient Population and Test Utilization for Thyroid Function in Local Clinics and Hospitals in Korea.

We evaluated the utilization and characteristics of thyroid function test (TFT) results, including serum thyroid stimulating hormone (TSH), free thyroxine (free T4), and total triiodothyronine (total T3) in Korean adults who visited local clinics and hospitals between 2018 and 2020. We obtained TFT results for 69,575 specimens from 47,685 adult Korean patients (4878 men and 42,807 women) with a mean age of 42.7 (standard deviation of 13.2) years. Among them, 23,581 specimens were tested for TSH only, 38,447 specimens were tested for TSH and free T4 (including 17,978 specimens without total T3), and 20,469 specimens were tested for all three, i.e., TSH, free T4, and total T3. The proportion of euthyroid was 80.0% among all 69,575 specimens, 71.2% among specimens with TSH and free T4, and 64.2% among specimens with all three TFTs. TFT patterns that were difficult to interpret and needed more clinical information were observed for about 6.9% of the 20,469 specimens with all three TFTs. Among the 20,469 specimens with all three TFTs, no specimen had increases in all three. Information on the prevalence of specimen results of TFTs would be helpful to expand our knowledge of patient population characteristics and to improve test utilization.

Reference intervals of anti-Müllerian hormone in Korean women.

BACKGROUND: Limited data are available with reference intervals of serum anti-Müllerian hormone (AMH) level in Korean women. METHODS: We retrospectively reviewed serum AMH test results performed with automated electrochemiluminescence immunoassay in Korean women who visited health promotion centers between January 2019 and December 2020. Serum AMH results by age group were compared with previously reported reference intervals. RESULTS: During the 2-year study period, a total of 1953 AMH test results from Korean women (age 20-49 years) undergoing general health checkups were obtained. Serum AMH level differed significantly by age group. Peak AMH level was observed at age 25-29 years and decreased to undetectable for subjects older than 44 years. The 2.5th, 5th, and 10th percentile values of the present study were comparable with previously assessed lower limits of reference intervals. The upper limit of the reference interval defined as the 97.5th percentile value in women younger than 35 years was higher than that of Western populations. The 90th percentile value of the present study population was similar to the 95th or 97.5th percentile value of reference intervals for Western populations of women younger than 35 years. CONCLUSION: Understanding patient populations and differences in reference intervals by age group and measurement method can help guide clinical decisions and clinical laboratory analysis.

Recent information on test utilization and intraindividual change in anti-glutamic acid decarboxylase antibody in Korea: a retrospective study.

INTRODUCTION: This study aimed to evaluate the test utilization and intraindividual changes of anti-glutamic acid decarboxylase antibody (GADA), a biomarker for autoimmune diabetes in Korean adults. RESEARCH DESIGN AND METHODS: We retrospectively investigated longitudinally measured GADA test results to assess test utilization and intraindividual changes through a laboratory information system. RESULTS: During the 3-year study period, 11 668 GADA tests were performed in 11 184 Korean adults. The overall rate of GADA positivity at initial measurement was 7.8%. Among the 11 668 test results, 871 GADA test results from 401 Korean patients (228 men and 173 women) requested by 54 hospitals were analyzed for intraindividual changes. Among these 401 patients, 80 (20.0%) had positive (≥2.0 U/mL) and 35 (8.7%) had gray zone GADA (1.0-1.9 U/mL) level at initial measurement. The prevalence of GADA-positive patients based on initial measurement was significantly different by type of medical institution. Among 80 patients with initial positive results, 5 (6.3%) experienced qualitative GADA changes during follow-up. Among the 321 patients with initially negative or gray zone GADA, 9 (2.8%) changed to GADA positive at least once during follow-up. CONCLUSIONS: Although most patients had stable GADA results, some exhibited qualitative changes during follow-up. This study can help to understand the variation in GADA positivity in the monitored patients.