Establishment of Reference Intervals of Cytokeratin 19 Fragment Antigen 21-1 in Korean Adults

Cytokeratin 19 fragment antigen 21-1 (CYFRA 21-1) is useful for predicting and monitoring non-small cell lung cancer prognosis. We established reference intervals (RIs) of CYFRA 21-1 in Korean adults, including those older than 60 years. Data of 4,098 apparently healthy subjects (age range, 20–87 years) were analyzed after excluding those with a history of malignancy, high tumor marker concentrations (except CYFRA 21-1), and/or abnormal findings on a chest computed tomography scan through medical chart review. After removing two outliers, RIs of CYFRA 21-1 were determined using data of 4,096 subjects based on the non-parametric method (2.5th and 97.5th percentiles) according to CLSI guidelines EP28-A3c. The subjects were divided into two and four groups according to sex and age (20–40, 41–50, 51–60, and >60 years), respectively, and the median CYFRA 21-1 concentration was compared between the groups. The RI of CYFRA 21-1 was 0.66–3.84 ng/mL, applicable to both men and women. Regardless of sex, the CYFRA 21-1 concentration increased with age, suggesting that age-dependent RIs of CYFRA 21-1 should be applied. Rather than using a single RI provided by the manufacturer, the RI of CYFRA 21-1 should be continually verified and established in each clinical laboratory.