# Student Handout: Immune Checkpoint Inhibitor Nephrotoxicity

> **Learning objective:** Understand the epidemiology, pathophysiology, clinical presentation, and management approach to immunotherapy-related kidney injury

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## What Are ICIs?

Immune checkpoint inhibitors are a revolutionary class of immunotherapy drugs used across many cancer types:

| Drug            | Target                           | Examples                 |
|-----------------|----------------------------------|--------------------------|
| **Anti-PD-1**   | Programmed death receptor 1      | Nivolumab, pembrolizumab |
| **Anti-PD-L1**  | PD-1 ligand                      | Atezolizumab, durvalumab |
| **Anti-CTLA-4** | Cytotoxic T-lymphocyte antigen 4 | Ipilimumab               |

**Key concept:** These drugs release immune brakes, activating T cells to attack cancer—but sometimes attack the kidneys too.

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## Epidemiology

- **Frequency:** 1–3% of ICI-treated patients develop clinical nephrotoxicity
- **Severity:** Most Grade 1–2 (mild), but Grade 3–4 (severe) requires discontinuation
- **Timing:** Usually occurs within 3–6 months, but can appear later
- **Risk factors:** Baseline CKD, diabetes, prior nephrotoxic drugs, combination therapy (ICI + CTLA-4 higher risk)

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## Pathophysiology: How ICIs Injure the Kidney

**The mechanism (simplified for PA level):**

1.  **Checkpoint release** — Anti-PD-1/PD-L1 or anti-CTLA-4 blocks inhibitory signals
2.  **T-cell activation** — T cells hyperactivate against cancer antigens
3.  **Cross-reactivity** — T cells recognize epitopes in kidney tubules and glomeruli
4.  **Inflammation** — Predominantly **acute interstitial nephritis (AIN)**, less commonly glomerular disease
5.  **Result:** Tubular damage → ↑ creatinine, proteinuria, microscopic hematuria

**Why AIN?** Mechanism mirrors classic drug-induced AIN, but driven by immune activation rather than direct toxin.

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## Clinical Presentation & Diagnosis

### Typical Picture

- **Asymptomatic ↑ creatinine** (40–90% of cases)
- **Baseline:** Usually occurs 3–6 months post-initiation
- **Labs:**
  - ↑ Serum creatinine (often 1.5–3× baseline)
  - ↑ BUN
  - Proteinuria (usually \<2 g/day unless glomerular)
  - Microscopic or gross hematuria possible
  - **Sterile pyuria** (hallmark)
  - ↓ Complement (usually normal)

### Diagnostic Approach

| Step | Action | Finding |
|----|----|----|
| **1. Suspect ICI nephrotoxicity** | Timeline (Cr ↑ during/after ICI) | Clinical probability high |
| **2. Check urine** | Urinalysis, urine Pt-Cr ratio | AIN: sterile pyuria, granular casts, muddy casts |
| **3. Check labs** | BMP, LDH, phosphate, uric acid | Normal complement distinguishes from GN |
| **4. Assess volume** | Physical exam, I/Os | Usually euvolemic or hypervolemic |
| **5. Consider biopsy** | If uncertain OR grade 3–4 AKI | Confirms AIN vs glomerular; guides further management |

### When to Biopsy

**Strongly consider** if: - Persistent Grade 3–4 AKI after 3–5 days of corticosteroids - Rapidly worsening renal function despite treatment - Need to rule out alternative pathology (GN, thrombotic, infection) - Considering rechallenge with ICI

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## Pathology (Brief)

If a biopsy is done:

| Finding | Interpretation |
|----|----|
| **Tubuloint. nephritis** | Lymphocytic infiltration of tubules and interstitium (dominant) |
| **Tubular damage** | Acute tubular injury, flattened epithelium |
| **Glomeruli** | Usually spared (unlike classic drug allergy); some cases show RPGN or membranous |
| **IF microscopy** | Usually negative (no immune complex deposition) |

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## Management Algorithm

### Mild (Grade 1–2) AKI

**Creatinine ≤1.5× baseline or \<50% ↑ from pretreatment baseline**

1.  **Hold ICI** — Pause immunotherapy during kidney injury recovery
2.  **Supportive care** — Ensure euvolemia, avoid nephrotoxins, monitor labs (Cr, BUN q2–3 days)
3.  **Monitor & reassess** — 60–70% recover spontaneously within 2–3 weeks
4.  **Restart** — If Cr recovers toward baseline AND clinical improvement, may cautiously resume ICI (risk of recurrence ~10–15%)

### Moderate (Grade 2–3) AKI

**Creatinine 1.5–3× baseline**

1.  **Hold ICI immediately**
2.  **Empiric corticosteroids:**
    - **Methylprednisolone 0.5–1 g IV daily × 1–3 days**, then taper
    - OR **Prednisone 0.5–1 mg/kg PO daily, taper over 4–6 weeks**
3.  **Supportive care** — Hydration, avoid NSAIDs/ACEi if severely reduced GFR
4.  **Monitor** — Cr, BUN, electrolytes q2–3 days
5.  **Response:**
    - **Good response (Cr ↓ 25%+ within 3–5 days)** → Continue corticosteroid taper, consider resumption of ICI at completion of steroid course
    - **Poor response (no improvement in 3–5 days)** → Escalate to Grade 3–4 protocol

### Severe (Grade 3–4) AKI

**Creatinine \>3× baseline OR need for dialysis**

1.  **Discontinue ICI** — Permanent discontinuation typically recommended
2.  **Aggressive corticosteroids:**
    - **Methylprednisolone 1 g IV daily × 3 days**, then switch to PO prednisone 1 mg/kg daily with taper over 6–12 weeks
3.  **Consider immunosuppression:**
    - If **no response within 3–7 days**, add **infliximab 5 mg/kg IV** (TNF-α inhibitor)
    - Or **mycophenolate mofetil (MMF) 1–1.5 g BID** for RPGN-pattern disease
4.  **Supportive:**
    - Renal replacement therapy if oliguria, hyperkalemia, severe fluid overload, metabolic acidosis
    - Monitor closely; some patients require long-term dialysis (10–15%)
5.  **Prognosis:** 30–40% recover renal function; others have chronic kidney disease

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## Special Considerations

### Combination Therapy (ICI + ICI)

- Anti-CTLA-4 + anti-PD-1 (e.g., ipilimumab + nivolumab) = higher nephrotoxicity risk (~5–10%)
- If AKI develops, usually higher grade → More likely to require aggressive immunosuppression

### Atypical Presentations

- **Glomerular disease:** Some patients develop RPGN, membranous nephropathy, or crescentic GN (10–20% of ICI-AKI)
  - Clue: RBC casts, hypertension, nephritic sediment → Biopsy
- **Hyperkalemia without severe AKI:** Type 4 RTA-like picture (aldosterone suppression)

### Monitoring After Recovery

- Serial creatinine even after recovery (relapse possible)
- If rechallenge ICI: More frequent Cr monitoring (weekly × 4, then biweekly)
- Consider baseline and periodic kidney biopsy if considering re-initiation after Grade 3–4 AKI

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## Key Clinical Pearls

✓ **Diagnosis:** AIN on biopsy; sterile pyuria is a clue ✓ **Timing:** Usually 3–6 months post-ICI initiation ✓ **Mild cases:** Often resolve with ICI hold + supportive care ✓ **Moderate–Severe:** Require corticosteroids ± immunosuppression ✓ **Escalate:** If no improvement in 3–5 days → infliximab/MMF ✓ **Prognosis:** Mild/Mod often recover; Severe may require long-term dialysis

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## Related Clinical Content

For more detailed information, see the Onconephrology Hub:

- ICI Fundamentals & Mechanisms — Deeper mechanistic review
- ICI Kidney Injury: Diagnosis & Pathology — Comprehensive diagnostic algorithms
- ICI Nephrotoxicity Treatment — Extended management protocols
- ICI Glomerular Diseases — Atypical presentations (RPGN, MN, ANCA)

**Cross-reference:** - Acute Kidney Injury Hub — General AKI workup framework - Student Handout: AIN — Detailed acute interstitial nephritis overview

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## References

- Kidney Disease: Improving Global Outcomes (KDIGO) Blood Pressure Work Group. KDIGO 2021 Clinical Practice Guideline for the Management of Blood Pressure in Chronic Kidney Disease. Kidney Int. 2021;99(3S):S1. [PubMed](https://pubmed.ncbi.nlm.nih.gov/33637192/)
- Cortazar FB, Marrone KA, Troxell ML, et al. Clinicopathological features of acute kidney injury associated with immune checkpoint inhibitors. Kidney Int. 2016;90(3):638. [PubMed](https://pubmed.ncbi.nlm.nih.gov/27282937/)
- Moledina DG, Perazella MA. Drug-Induced Acute Interstitial Nephritis. Clin J Am Soc Nephrol. 2017;12(12):2046. [PubMed](https://pubmed.ncbi.nlm.nih.gov/28893923/)
- Cortazar FB, Kibbelaar ZA, Glezerman IG, et al. Clinical Features and Outcomes of Immune Checkpoint Inhibitor-Associated AKI: A Multicenter Study. J Am Soc Nephrol. 2020;31(2):435. [PubMed](https://pubmed.ncbi.nlm.nih.gov/31896554/)

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**Study Tips:** - Use the management algorithm table when seeing ICI patients - Memorize the 3 grades and corresponding corticosteroid dosing - Remember: AIN is the dominant pathology; think of it like an immune drug allergy - Infliximab is your “rescue” drug for failures

*Created: 2026-02-28*

### Also on this topic

The same subject at other levels of depth.

- **Clinical Mastery deep dive:** [Immune Checkpoint Inhibitor Nephrotoxicity](https://urinenephrology.org/mastery/onconephrology/ici-nephrotoxicity.html)


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