High levels of CRP in morbid obesity: the central role of adipose tissue and lessons for clinical practice before and after bariatric surgery

Background: Obesity, characterized by low-grade inflammation both in blood and white adipose tissue (WAT) is associated with increased C-reactive protein (CRP), a well-known acute phase protein. The aim of this study was to determine factors associated with high levels of CRP in obesity.

Methods: In 674 obese patients candidates to bariatric surgery (mean body mass index [BMI]=47.4±7.4 kg/m²), we examined the relationships between CRP and a series of bioclinical markers and histologic features of subcutaneous and omental WAT (scWAT) and liver. We also compared the same parameters after separating patients with "high" inflammation (HI, CRP≥20 mg/L, n=52) and with "low" inflammation (LI, CRP<20 mg/L, n=622).

Results: Mean CRP was 8.9±6.9 mg/L and positively correlated with fat mass (P<10(-4)). The HI group included predominantly women (92% versus 79%), of a younger age, with higher BMI (50.9±8.8 versus 47.1±7.2 kg/m2, P=.003), and fat mass (51.6 versus 48.8%, P<.001), higher prevalence of obstructive sleep apnea (OSA) (73% versus 57%, P=.02), and had increased number of HAM56+ immune cells in scWAT (20.8 versus 14.5%, P=.05). There was no difference in metabolic status, WAT fibrosis or liver histology findings between the groups. After 1 year of surgery-induced weight loss, 48 out of 52 patients with HI returned to CRP levels<20 mg/L.

Conclusion: Our results suggest that WAT inflammation is a major contributor to increased CRP in obesity. In obese patients presenting high CRP levels with no obvious explanation, age, gender, BMI, fat mass proportion, OSA, and WAT inflammation should be taken into account to decide to perform further additional medical investigations.