Hyein Kang

Background: Serum amyloid A (SAA) is an acute-phase reactant that increases rapidly in response to inflammatory stimuli and infection, earlier and more markedly than conventional markers such as C-reactive protein (CRP). However, large-scale evidence of its clinical utility in bloodstream infections (BSIs) remains limited. This study aimed to evaluate the diagnostic and prognostic value of SAA in patients presenting to the emergency department (ED) with suspected infection. Methods: We retrospectively reviewed the electronic medical records of adult patients who underwent simultaneous SAA and blood culture (BC) testing at the ED of a tertiary referral hospital between January and December 2025. Initial laboratory data, including CRP, procalcitonin (PCT), white blood cell (WBC) count, and absolute neutrophil count (ANC), were collected, and BSI was defined as the isolation of pathogenic organisms in BC. Correlations and agreement between SAA and other markers were assessed, and the diagnostic performance of BSI was evaluated using receiver operating characteristic curves and the area under the curve (AUC). Survival outcomes were analyzed using the Kaplan–Meier method. Results: Among the 3321 included patients, 379 patients (11.4%) had positive BCs. Median SAA levels were significantly higher in BSI patients than in non-BSI patients (202.0 vs. 71.0 mg/L, p < 0.001), with the highest levels observed in Gram-negative infections. SAA showed a strong correlation with CRP (r_s = 0.884) and a moderate correlation with PCT (r_s = 0.576). The AUC for BSI diagnosis was highest for PCT (0.789), followed by SAA (0.650). The SAA demonstrated high sensitivity (90.5%) but low specificity (26.9%). Higher SAA levels were significantly associated with increased mortality rates. Conclusions: In adult ED patients, SAA is significantly associated with BSI and mortality and is a sensitive biomarker for the early detection of BSIs. Although SAA alone showed inferior discriminative performance compared to PCT, it may serve as an adjunctive screening tool in the ED, particularly in settings where PCT availability is limited.

Sunggyun Park and Hyein Kang. Lab Med Qual Assur 2026;48:1-4. https://doi.org/10.15263/jlmqa.2026.48.1.1

Hyein Kang, Hanmil Jang, John Hoon Rim, Sang-Guk Lee, and Jong-Baeck Lim. Lab Med Qual Assur 2025;47:23-7. https://doi.org/10.15263/jlmqa.2025.47.1.23

Kyoung Bo Kim, M.D., Gi Su Lee, M.D., Soyoung Shin, Ph.D., Dong-Chan Kim, Ph.D. , Donggun Seo, B.S.P.H., Hyeongjin Kweon, B.S., Hyein Kang, M.D, Sunggyun Park, M.D., Do-Hoon Kim, Ph.D., Namhee Ryoo, Ph.D., Soyoung Lee, Ph.D., and Jung Sook Ha, Ph.D.. Ann Lab Med -0001;0:. https://doi.org/10.3343/alm.2024.0226

Background: While the real-world impact of estimated glomerular filtration rate (eGFR) equation change on clinical outcome in a longitudinal cohort setting is limited, external valuation of equation performance should be performed in different population cohorts. This study aimed to compare differential impacts of eGFR values, calculated by 5 equations in a Korean patient population, on clinical outcomes. Methods: This retrospective longitudinal follow-up cohort study analyzed 23 246 participants with standardized creatinine/cystatin C assay-based laboratory results. The primary exposure was baseline eGFR calculated by 5 different equations including the recently developed 2021 race-free Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations. Clinical outcomes including all-cause mortality, renal replacement therapy, and albuminuria were analyzed to estimate the hazard ratio of the eGFR on clinical outcomes. Results: Among the 5 equations, CKD-EPI 2021 with creatinine and cystatin C (CKD-EPI 2021-CrCys) showed an earlier increase in hazard ratios for all clinical outcomes, while CKD-EPI 2012 with cystatin C showed a higher hazard ratio for all-cause mortality at low eGFR. Replacing CKD-EPI 2012 with CKD-EPI 2021-CrCys, 5.4% of patients with mortality and 3.3% of patients who received renal replacement therapy were reclassified to a lower risk stage. Conclusions: The 2021 CKD-EPI equations were acceptable in a Korean population, with better predictive power for clinical outcomes when compared to previous equations. The updated race-free factors for eGFR calculation improved identification of patients at risk for clinical outcomes.

Hanmil Jang, Jaehyeok Jang, Hyein Kang, John Hoon Rim, and Jong-Baeck Lim. Lab Med Qual Assur 2024;46:60-5. https://doi.org/10.15263/jlmqa.2024.46.1.60

Jeongyun Bae, M.D., Won Kee Ahn, M.D., Jaehyeok Jang, M.D., Hanmil Jang, M.D., Hyein Kang, M.D., John Hoon Rim, M.D., Ph.D., Seung Min Hahn, M.D., Jung Woo Han, M.D., Chuhl Joo Lyu, M.D., Ph.D., and Jong-Baeck Lim, M.D., Ph.D.. Ann Lab Med 2024;44:97-9. https://doi.org/10.3343/alm.2024.44.1.97

Objectives: Free light chain (FLC) is used for the diagnosis and prediction with regard to the progression risk of plasma cell disorders and Freelite reagent using the SPAplus analyzer (The Binding Site) has been one of the widely used option. However, N Latex FLC reagent with the Atellica CH 930 analyzer (Siemens Healthineers) has shown the advantages of automation and high throughput. We aimed to evaluated clinical implication by differential analytical performances of two assays. Methods: A total of 322 serum samples were collected from 193 patients requested for FLC analysis including 131 multiple myeloma patients. The precision, linearity, dilution recovery of N Latex FLC assay was evaluated. We compared the two assays and analyzed the monomer-dimer pattern for discrepant results. Results: The precision, linearity, and dilution recovery performance was appropriate for the routine use in clinical laboratories. Despite the good correlation within normal range, proportional bias up-to 170% was observed in samples with high concentrations especially for lambda. The higher value samples with N Latex FLC assay contained more monomer forms than controls. All opposite changes of FLC burden by the N Latex FLC assay proved to present concordant dynamic changes when assessed by serum protein electrophoresis. Conclusions: Clinical laboratories should be aware of the inter-assay variability of FLC quantitative measurements using different platforms, especially for high concentrations of both kappa and lambda measurements, possibly due to monomer/dimer ratio diversity. Clinical interpretations for multiple myeloma disease status might not be dramatically affected only when the same assay is utilized during follow-up periods.