Measuring inflammation in psychiatric patients is straightforward in principle and slightly nuanced in practice. The core measurements are accessible, inexpensive, and informative when interpreted in the context of the patient's presentation. The clinical task is to know which markers to order, in which patients, with what frequency, and how to translate the results into intervention.
High-sensitivity C-reactive protein (hs-CRP) is the workhorse inflammatory marker. CRP is produced by the liver in response to IL-6 signaling and is the most widely available and validated peripheral inflammation marker. Values under 1 mg/L are low risk, 1–3 mg/L are intermediate, and over 3 mg/L are elevated risk for cardiovascular and cognitive outcomes. Acute illness, infection, recent surgery, and active autoimmune disease produce dramatic CRP elevations and must be excluded before interpreting persistent moderate elevation as chronic inflammation. The clinical move is to order hs-CRP in every patient in the acceleration window and in any patient with refractory psychiatric illness, repeating at intervals when interventions are underway.
Interleukin-6 (IL-6) is more directly mechanistic but less widely available. IL-6 drives CRP production and has direct effects on mood, cognition, and metabolic function. When elevated, it identifies inflammation in a more proximal way than CRP. Clinical applications include refractory depression workup (where CRP is borderline or where the clinical picture suggests inflammation despite normal CRP) and characterization of inflammatory burden when intervention is being targeted. Cost has come down; availability varies by laboratory and region.
TNF-alpha is another pro-inflammatory cytokine with relevance to psychiatric illness, particularly depression and bipolar disorder. Like IL-6, it is more direct but less widely available than CRP. Its clinical role is limited in most settings because the test is expensive, less standardized, and rarely actionable beyond what CRP and IL-6 already inform. Reserve for specialty workup in refractory cases where comprehensive inflammation characterization is being pursued.
Ferritin is technically an iron-storage protein but functions as an acute phase reactant that rises in inflammation. Elevated ferritin without identifiable iron-loading cause (no hemochromatosis, no transfusion history) is an inflammatory signal. Conversely, low ferritin identifies iron deficiency, which has its own psychiatric and cognitive consequences (depression, fatigue, restless legs, cognitive impairment, particularly in menstruating women). Ferritin is inexpensive, widely available, and informative on both ends of the range — order it routinely.
The clinical interpretation framework. A patient with persistent CRP over 3 mg/L without identifiable infectious or autoimmune cause has chronic inflammation that warrants intervention. The first move is workup for source: dental disease, undiagnosed sleep apnea, GI inflammation, smoldering autoimmune process, metabolic syndrome. The second is targeted intervention: sleep optimization, exercise, dietary anti-inflammatory pattern, weight management, omega-3, treatment of any identified source. The third is monitoring: repeat CRP at 8–12 weeks to track movement. The pattern that emerges over months is the actionable clinical data — persistent inflammation that does not respond to lifestyle intervention identifies patients where pharmacological anti-inflammatory strategies become reasonable considerations.