Exploration for the reference interval of C-reactive protein in the Chinese longevity people over 90 years of age

Older individuals tend to develop chronic inflammation. As a commonly used nonspecific inflammatory marker, C-reactive protein (CRP) can predict metabolic syndrome, cardiovascular diseases, etc. However, little is known about CRP levels in longevity people. Investigate the distribution and correlates of CRP and provide a reference for the establishment of normal interval values in Chinese longevity people over 90 years of age. We performed a correlation analysis to evaluate the correlation between CRP levels and longevity based on the basic demographic characteristics, anthropometric measurements and blood data of 4,418 participants in the 2015 China Health and Retirement Longitudinal Study and 636 participants in an ongoing longitudinal study of natural longevity people in Guangxi. On this basis, the CRP reference interval for longevity was explored. The CRP concentration was significantly different among the three age groups, with a median of 3.80 mg/L for those older than 90 years, which was significantly higher than that for those aged 45–64 years (median 1.20 mg/L, p < 0.001) and 65–89 years (median 1.30 mg/L, p < 0.001). Body mass index, waist circumference, the waist-to-height ratio, systolic blood pressure, diastolic blood pressure, and fasting and postprandial blood glucose, triglyceride, total cholesterol and low-density lipoprotein cholesterol levels were positively correlated with CRP levels, while fasting high-density lipoprotein cholesterol was negatively correlated with CRP levels. The CRP reference interval (RI) value in longevity people was 0.25–9.22 mg/L. The concentrations of CRP increased with advancing age, and the CRP reference interval was different between older and younger adults.