Ann Lab Med.  2025 May;45(3):291-299. 10.3343/alm.2024.0317.

Adjustment Formula for Harmonizing Triglyceride Values in the Korea National Health and Nutrition Examination Survey, 2005–2022

• Choi R
• Seo JD
• Cho EJ
• Lee W
• Yun YM

• KMID: 2567972
• DOI: http://doi.org/10.3343/alm.2024.0317

Abstract

Background
Korea National Health and Nutrition Examination Survey (KNHANES) triglyceride testing changed from the glycerol blanking method (2005–2021) to the glycerol nonblanking method (2022). We converted triglyceride data from 2005–2021 to that obtained since 2022 with different analytical methods.
Methods
To develop a conversion equation, 98 fresh serum specimen pairs were compared using Passing–Bablok regression analysis. Implications of the conversion equation on epidemiological data were evaluated using KNHANES data from 2019–2021. Bias estimations determined using the Lipid Standardization Program (LSP) of the United States Centers for Disease Control and Prevention (CDC) enhanced the accuracy and comparability of the triglyceride results.
Results
Triglyceride concentrations measured via the glycerol non-blanking method were 10.7 mg/dL (0.12 mmol/L, 10.0%) higher than those from the glycerol blanking method, with a 9.9 mg/dL (0.11 mmol/L, 5.0%) difference at a concentration of 200 mg/dL (2.26 mmol/L, N = 98). The conversion equation y (glycerol non-blanking, 2022) = 11.94+0.99x (glycerol blanking, 2005–2021) changed the mean triglyceride concentrations of the KNHANES 2019–2021 data (N = 16,015) from 123.7 mg/dL (1.40 mmol/L, 95% confidence interval [CI]: 122.2–125.1 mg/dL [1.38–1.41 mmol/L]) to 134.3 mg/dL (1.52 mmol/L, 95% CI: 132.9–135.8 mg/dL [1.50–1.53 mmol/L]). Since 2022, bias monitoring using the CDC’s LSP has remained within a 5.0% limit.
Conclusions
KNHANES triglyceride values in 2022 (non-blanking) were substantially higher than those from 2005–2021 (blanking). Conversion equations helped effectively adjust 2005–2021 data. Researchers should consider adjusting the KNHANES triglyceride data based on their study characteristics.

Keyword

Calibration; Data Processing; Korea National Health and Nutrition Examination Survey; Standardization; Triglycerides

Figure

• 

  Fig. 1 Flow diagram for the study. As the analytical methods for triglyceride measurement in KNHANES transitioned from glycerol blanking methods (2005–2021) to glycerol non-blanking methods (2022 onward), a conversion equation was developed to adjust for differences in triglyceride values. The equation was derived from comparison studies that evaluated triglyceride values obtained using glycerol blanking methods (2021) and glycerol non-blanking methods (2022) at the KNHANES laboratory. The application of this conversion equation was assessed using KNHANES triglyceride values from 2019 to 2021 as an example. A triglyceride concentration of 200 mg/dL is equivalent to 2.26 mmol/L. Abbreviation: KNHANES, Korea National Health and Nutrition Examination Survey.

• 

  Fig. 2 Comparison study of triglyceride measurements. (A) Scatter plot with Passing–Bablok regression analysis depicting the relationship between triglyceride measurements obtained using the X method with KNHANES 2021 data (glycerol blanking) at Seegene Medical Foundation and the Y method with KNHANES 2022 data (glycerol non-blanking) at GC Labs. The solid 45° line indicates the line of identity, and points represent individual paired measurements from the two methods. (B) Bland–Altman plot showing differences in triglyceride concentrations (mg/dL). (C) Bland–Altman plot showing percent differences in triglyceride concentrations (%). The solid blue line in the Bland–Altman plots represents the mean difference and mean percent difference, with a 95% confidence interval indicated by dotted blue lines. Solid gray lines are drawn at zero. Abbreviation: KNHANES, Korea National Health and Nutrition Examination Survey.

• 

  Fig. 3 Serum triglyceride levels in KNHANES participants before and after conversion. Kernel density plots represent serum triglyceride data from KNHANES 2019–2021 (N=16,015) and KNHANES 2022 (N=4,996), excluding pregnant women and non-fasting individuals (<12 hrs), before and after adjustment using the conversion equation y (glycerol non-blanking, mg/dL)=11.94 (mg/dL)+0.99x (glycerol blanking). The blue curve represents data before conversion, and the red curve shows data after conversion. The X-axis represents serum triglyceride levels, and the Y-axis depicts the fraction of the population in density plots, estimated using kernel density functions with the area under the curve integrated into one. The vertical gray dotted line marks the triglyceride level of 200 mg/dL (2.26 mmol/L), as defined by the National Cholesterol Education Program Adult Treatment Panel III criteria for high triglyceride levels. For presentation purposes, triglyceride values ≥500 mg/dL (5.65 mmol/L) were converted to 500 mg/dL (5.65 mmol/L). Abbreviation: KNHANES, Korea National Health and Nutrition Examination Survey.

• 

  Fig. 4 Percent bias change for triglyceride measurements from the CDC Lipid Standardization Program (LSP) during KNHANES (2018–2022). During KNHANES 2018–2021, triglyceride measurements were performed using glycerol blanking methods at Seegene Medical Foundation, whereas in KNHANES 2022, measurements were performed using glycerol non-blanking methods at GC Labs. The X-axis represents each survey round and specimen identifier (labeled as PS-survey round-specimen identifier). Bars represent percent bias estimates calculated by the CDC LSP for each round. The blue dotted lines indicate the upper and lower allowable bias limits (±5%) defined by NCEP ATP III criteria. Green arrows denote calibrator lots used during survey rounds; yellow arrows indicate reagent lots; blue arrows represent the survey year; and black arrows show the analytical methods used during these rounds. The CDC LSP survey sets target values using glycerol non-blanking methods, represented by a thin gray line at 0.0%. Blue bars represent results below the target values assigned by CDC mean values, orange bars indicate results above target values, and dark blue bars represent results exceeding the ±5% bias limit. Percent bias was calculated using the formula: (Result from each lab − CDC mean [target])/CDC mean (target)×100. Abbreviation: KNHANES, Korea National Health and Nutrition Examination Survey.

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