To evaluate liver functional reserve in healthy subjects of different age groups using the L-[1-¹³C]-phenylalanine breath test(¹³C-pheBT)and to investigate the patterns of changes in liver functional reserve with aging in comparison with elderly cirrhosis patients.

Thirty-seven healthy volunteers were divided into a young and middle-aged group(n=10), an early elderly group(n=9), an advanced elderly group(n=9)and a longevity group(n=9). Eight elderly patients with liver cirrhosis were selected as the control group.An oral dose of 100 mg ¹³C-phe was administered to each subject.Expired breath samples were collected at pre-dose and at 12 different time points within 150 minutes post-dose.Isotope ratio mass spectrometer was used to measure the abundance of ¹³C.The percentage of the ¹³C excretion rate(¹³CO₂ERt), the percentage of ¹³C cumulative excretion(¹³Ccumt)at different time points, and the percentage of the ¹³C peak excretion rate(¹³CO₂ERmax)after drug administration were calculated.In addition, associations between¹³C-pheBT and common liver function parameters were analyzed.

Compared with healthy volunteers, ¹³CO₂ER₃₀, ¹³CO₂ER₄₅, ¹³CO₂ER₆₀, ¹³Ccum₄₅, ¹³Ccum₆₀, ¹³Ccum₇₅, ¹³Ccum₉₀ and ¹³Ccum₁₀₅, ¹³Ccum₁₂₀, ¹³Ccum₁₃₅, ¹³Ccum₁₅₀ showed significant differences in the longevity group, the young and middle-aged group and the young elderly group.There were statistically significant differences between the elderly cirrhosis group and the healthy volunteers in each subgroup(all P<0.05); The mean values of ¹³CO₂ERmax, ¹³CO₂ER₃₀, ¹³Ccum₄₅, ¹³Ccum₆₀, ¹³Ccum₇₅, ¹³Ccum₉₀, ¹³Ccum₁₀₅, ¹³Ccum₁₂₀, ¹³Ccum₁₃₅, ¹³Ccum₁₅₀ decreased following the order of the young and middle-aged group, the early elderly group, the advanced elderly group, the longevity group, and the elderly cirrhosis group(all P<0.05). In healthy volunteers, the ¹³CO₂ exclusion rate curve and the cumulative exclusion rate curve showed that the curves of the young and middle-aged group and the early elderly group almost overlapped, while the curves of the advanced group and the longevity group decreased with age, and the difference between the longevity group and the young and middle-aged group and between the longevity group and the early elderly group was markedly prominent.

¹³C-pheBT is a safe, sensitive and reliable test for quantitation of liver function.Our recommendations include collecting samples within an hour of drug administration and using ¹³CO₂ERmax, ¹³CO₂ER₃₀, ¹³Ccum₄₅ and ¹³Ccum₆₀ as the main parameters.Overall, the functional reserve and compensatory capability of the liver are robust.The decline in liver functional reserve in healthy individuals is a gradual and slow process, with a significant decrease after age 80 and more so after age 90.

Phenylalanine; Breath test; Liver functional reserve