Serum ferritin/C-reactive protein ratio is a simple and effective biomarker for diagnosing iron deficiency in the context of systemic inflammation

• Published in: QJM : An International Journal of Medicine Vol. 117; no. 1; pp. 9 - 15
• Main Authors: Urbanski, G, Chabrun, F, Lavigne, C, Lacout, C, Delattre, E, Reynier, P, Requin, J
• Format: Journal Article
• Language: English
• Published: England 07.02.2024
• ISSN: 1460-2725; 1460-2393
• DOI: 10.1093/qjmed/hcad218

Diagnosing iron deficiency is challenging in the presence of systemic inflammation. To investigate the relationship between plasma C-reactive protein (CRP), serum ferritin (SF) and transferrin saturation (TS), with the objective of establishing a straightforward ratio applicable in the presence of inflammatory syndrome. Test prospective cohort and validation retrospective cohort. A prospective cohort of inpatients (n = 140) assessed the correlation between CRP and SF/TS levels. The diagnostic performance of a determined ratio was evaluated for identifying iron deficiency (ID) using different definitions and in the presence of inflammation and/or chronic heart and/or kidney failure. A large validation cohort (n = 795) further assessed the predictive power of this ratio. In a training cohort (median age 76 years [57-84]), a linear relation was observed between SF (µg/l) and CRP (mg/l), unlike with TS. The SF/CRP ratio accurately predicted ID, with receiver operating characteristic-area under the curve (ROC-AUC) values ranging from 0.85 to 0.92 for different ID definitions. A threshold of ≤6 demonstrated the highest Youden index (0.61). In the validation cohort (age 72 years [57-84]), the SF/CRP ratio exhibited an ROC-AUC of 0.88 [95% CI: 0.85-0.90], with an odds ratio of 37.9 [95% CI: 20.3-68.9] for the threshold of ≤6. In this study, we demonstrated that the SF/CRP ratio, with a threshold of ≤6, is a simple and effective biomarker for ID, even in the presence of systemic inflammation or comorbidities. This ratio could potentially replace the complex set of criteria currently recommended by learned societies.