A Comparison of Complete Blood Count Reference Intervals in Healthy Elderly Versus Younger Korean Adults: A Large Population Study
Authors: Lee Young Kyung , Lee Eun Jin , Kim Miyoung , Lee Eunyup , Jeon Kibum , Lee Jiwon , Lee Jee-Soo , Kim Hyo Jung 
Published: October 2019

Abstract
Background: The use of laboratory reference intervals based on younger populations is of questionable validity in older populations. We established reference intervals for 16 complete blood count (CBC) parameters in healthy elderly Koreans aged ≥60 years and compared them to those of individuals aged 20-59 years.
Methods: Among 64,532 individuals (39,609 men and 24,923 women) aged ≥20 years who underwent medical check-ups, 8,151 healthy subjects (12.6%, 5,270 men and 2,881 women, including 675 and 511, respectively, who were ≥60 years of age) were enrolled based on stringent criteria including laboratory, imaging, and endoscopy results; previous medical history; and medication history. CBC parameters were measured using an Advia2120i instrument. The difference between 2 age groups in subjects of each sex was compared using the Mann-Whitney U-test. P-values <0.05 were considered statistically significant. The reference intervals for measured CBC parameters were established according to a nonparametric method based on the CLSI EP28A-3C in each subgroup. The 90% confidence intervals for the upper and lower limits of each reference interval were calculated; the Reed method was used to remove extreme outliers. The Harris and Boyd method was used to determine the necessity of separating the reference intervals for different age groups within each sex group. To identify reference intervals in different age groups in individuals aged 60 years and over, such individuals of each sex were subdivided into 5 age subgroups with 5-year age interval: since the sizes of 4 of these subgroups were not sufficiently large, we used the Robust method.
Results: A statistical difference in the medians of the following parameters were observed between the <60- and ≥60-year age groups: RBC, Hb, hematocrit (Hct), basophils, and platelets in men aged <60 years were higher than those in men aged ≥60 years; furthermore, MCV, MCH, and RDW in men aged ≥60 years were higher than those in men aged <60 years. Neutrophils in women aged <60 years were higher than in those aged ≥60 years. Hb, Hct, MCV, MCH, MCHC, lymphocytes, and basophils in women aged ≥60 years were higher than in those aged <60 years. Separate reference intervals were required only for RDW and MCH in women ≥60 from those < 60 years of age. Men aged ≥60 years versus those <60 years did not require separate reference intervals for any of the 16 measured parameters. In subjects aged ≥60 years, RBC, Hb, Hct, MCV, MCH, MCHC, RDW, WBC, neutrophils, monocytes, eosinophils, MPV, and PDW were higher in men than in women, while the opposite was true for lymphocytes and platelets. Partitioning of reference intervals by sex was required for RBC, Hb, Hct, MCH, monocytes, and eosinophils. In men, median values and the lower limits of the reference intervals for RBC, Hb, and Hct tended to decrease with advancing age. The upper and lower limits of reference intervals for WBC, neutrophils, lymphocytes, and MPV also showed increasing and decreasing tendencies, respectively, widening the reference intervals as the subjects aged (except in the 70-74-year-old group for men). Among women, the lower limits of the reference intervals for RBC, Hb, and Hct showed a tendency to decrease with increasing age for those >70 years of age; however, the median values did not show such a tendency. The reference interval for PDW narrowed as women aged. Separate reference intervals were required among men for MCH and eosinophils in the 70-74-year group, and for basophils in the 65-69-year group. Among women, separate reference intervals were required for MCV in the 65-69-year group; for MCH in the 60-64, 65-69, and ≥75-years groups; and for RDW in all the 4 elderly age subgroups.
Conclusion: Healthy elderly Koreans can use the same reference intervals as younger populations. Thus, abnormal CBC results may not necessarily be attributable to physiologic changes but possible underlying diseases that should be investigated.

Disclosures
No relevant conflicts of interest to declare.