Are Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) elevated in acute interstitial nephritis?

ESR and CRP in Acute Interstitial Nephritis

Yes, both ESR and CRP are typically elevated in acute interstitial nephritis (AIN), with ESR often markedly increased (mean ~85 mm/h) and CRP substantially elevated (mean ~81 mg/L), serving as important diagnostic clues for this condition. 1

Evidence for Inflammatory Marker Elevation

Direct Evidence from AIN Studies

• In drug-induced AIN, ESR and CRP are elevated in the vast majority of cases, with ESR elevated in 11 of 11 patients tested and CRP elevated in 12 of 12 patients where measured 1
• The mean ESR was 85 mm/h and mean CRP was 81 mg/L in a cohort of 15 PPI-induced AIN patients 1
• A systemic inflammation score (SIS) based on CRP and ESR levels correlates positively with the degree of active inflammatory cell infiltration in renal tissue in drug-induced AIN 2
• Higher SIS scores (indicating more elevated ESR/CRP) are associated with greater numbers of interstitial inflammatory cells, particularly neutrophils and plasma cells 2

Clinical Utility of These Markers

• Early diagnosis of AIN may be facilitated by clinician awareness of elevated ESR and CRP, particularly in cases with insidious onset where systemic allergic symptoms are absent 1
• The elevation of these inflammatory markers reflects the active tubulointerstitial inflammation occurring in AIN 2
• In TINU syndrome (tubulo-interstitial nephritis and uveitis), patients demonstrate markedly increased ESR and elevated serum immunoglobulin levels as part of the inflammatory syndrome 3, 4

Diagnostic Approach When AIN is Suspected

When to Consider AIN

• Unexplained acute kidney injury with elevated ESR and CRP should prompt consideration of AIN, especially in patients on medications known to cause this condition (NSAIDs, PPIs, antibiotics) 1
• Note that 11 of 15 patients in one series were asymptomatic with insidious development of renal failure, making inflammatory markers particularly valuable 1

Laboratory Evaluation

• Measure both ESR and CRP, as they provide complementary information about the inflammatory process 5, 6
• CRP rises and falls more rapidly than ESR, making it useful for acute diagnosis 7
• ESR has a longer half-life and may be more useful for monitoring chronic inflammation 7
• Complete blood count, electrolytes, liver enzymes, and renal function tests should be obtained 5, 6

Correlation with Pathology

• Higher inflammatory marker levels correlate with more active inflammation and less fibrosis on biopsy 2
• Patients with higher SIS scores (more elevated ESR/CRP) tend to have more favorable renal restoration with treatment 2
• The SIS can help guide therapeutic decisions when biopsy is contraindicated or refused 2

Important Clinical Caveats

• While elevated ESR and CRP support the diagnosis of AIN, neither marker is specific for this condition and can be elevated in many inflammatory, infectious, and malignant processes 5, 6
• Renal biopsy remains the gold standard for definitive diagnosis when feasible 2
• Factors such as anemia, female sex, and advanced age can artificially elevate ESR 6, 8
• The absence of elevated inflammatory markers does not exclude AIN, though it makes the diagnosis less likely 5