What do elevated Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) levels indicate?

What ESR and CRP Tell You

ESR and CRP are complementary inflammatory markers that indicate the presence and intensity of inflammation in your body, but they measure different aspects of the inflammatory response and should be interpreted together rather than as alternatives. 1, 2

Normal Values and What Elevation Means

• ESR is elevated when >20 mm/h in men and >30 mm/h in women, with values naturally increasing with age 1, 2, 3
• CRP is elevated when >10 mg/L, indicating significant active inflammation 1, 2
• Moderate ESR elevation (50-100 mm/h) suggests significant underlying disease, while values >100 mm/h have 92.2% specificity for serious conditions like giant cell arteritis 1, 2, 3

Key Differences Between ESR and CRP

• CRP rises and falls rapidly (within hours to days) because it has a short half-life, making it ideal for diagnosing acute infections and monitoring treatment response 4
• ESR changes slowly (over days to weeks) because it indirectly measures fibrinogen, which has a much longer half-life, making it better for monitoring chronic inflammatory conditions 4
• CRP is more specific for acute bacterial infections, particularly urinary tract, gastrointestinal, lung, and bloodstream infections 5
• ESR is more sensitive for chronic conditions like giant cell arteritis, polymyalgia rheumatica, and bone/joint infections 5

What Specific Diseases They Help Diagnose

Rheumatologic Conditions

• Both markers are incorporated into disease activity scores (DAS28) for rheumatoid arthritis and help monitor treatment response 6, 1, 2
• ESR >40 mm/h has 93.2% sensitivity for giant cell arteritis, with negative likelihood ratio of 0.18 3
• Polymyalgia rheumatica commonly presents with elevated ESR, and values >40 mm/h predict higher relapse rates 3

Infections

• In prosthetic joint infections, CRP has 73-91% sensitivity and 81-86% specificity when cutoff of 13.5 mg/L is used 6, 1, 2
• When both ESR and CRP are negative, prosthetic joint infection is unlikely per American Academy of Orthopedic Surgeons guidelines 6
• Highly elevated ESR (≥70 mm/h) has 81% sensitivity and 80% specificity for osteomyelitis in diabetic foot infections 3

Cardiovascular Disease

• In dialysis patients, elevated CRP predicts all-cause and cardiovascular mortality and may be a stronger predictor than LDL-cholesterol 6
• Ischemic strokes almost invariably occur with high ESR/low CRP pattern, while myocardial infarction shows high CRP/low ESR pattern 5

When Results Are Discordant

CRP/ESR discordance occurs in approximately 1 in 8 patients (12%), and the pattern tells you important diagnostic information 5:

• High CRP with low ESR suggests acute bacterial infections (urinary, GI, pulmonary, bloodstream), myocardial infarction, or venous thromboembolism 5
• High ESR with low CRP suggests connective tissue diseases (systemic lupus erythematosus), bone/joint infections, or ischemic stroke 5

Critical Factors That Falsely Elevate Results

ESR Falsely Elevated By:

• Anemia, female sex, and advanced age 6, 2, 3
• Azotemia (kidney dysfunction) 3
• Elevated immunoglobulins and rheumatoid factor 3

Both Markers Affected By:

• Underlying inflammatory arthropathy makes interpretation difficult 6
• Biologic agents targeting specific cytokines may disproportionately affect one marker, potentially masking disease activity 2

Diagnostic Algorithm When Both Are Elevated

1. Obtain complete blood count, electrolytes, liver enzymes, albumin, and renal function to assess for underlying causes 1, 2
2. Rule out infections with blood and stool cultures (including C. difficile and CMV if indicated) 2
3. Consider cross-sectional imaging (CT, MRI, ultrasound) to detect abscesses or fistulae if infection suspected 1, 2
4. For values >100 mm/h ESR, urgently evaluate for giant cell arteritis with temporal artery assessment and consider immediate specialist referral 3
5. If both markers remain elevated without clear cause, consider autoimmune workup (RF, anti-CCP, ANA, ANCA) only if clinical signs suggest specific conditions 3

Common Pitfalls to Avoid

• Neither marker is sufficiently specific or sensitive when used alone as a diagnostic tool 1
• Peripheral leukocyte counts are NOT elevated in most prosthetic joint infections, so don't rely on WBC alone 6
• In rheumatoid arthritis, ESR and CRP correlate poorly with clinical disease activity measures in routine care, so don't use them as sole indicators of disease control 7
• In elderly patients, both tests have limited utility with low true-positive/false-positive ratios, so interpret cautiously 8
• CRP returns to baseline within 2 months after surgery, so persistent elevation beyond this suggests ongoing pathology 6