ACUTE INTERSTITIAL NEPHRITIS

✓ Medically ReviewedDISEASEID: MDBT0209🚨 TRIAGE: URGENTICD-10: N10

📖

Definition

CLINICAL DEFINITION

Acute interstitial nephritis (AIN) is a clinicopathological syndrome characterised by acute inflammation and oedema of the renal interstitium and tubules, typically presenting with acute kidney injury (AKI). It is most frequently drug-induced, but can also result from infections or systemic autoimmune diseases.

IN PLAIN ENGLISH

A sudden inflammation of the spaces between the kidney tubules, often caused by an allergic reaction to medications, which can lead to a rapid drop in kidney function.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Acute Interstitial Nephritis is NOT acute tubular necrosis (ATN); while both cause acute kidney injury, AIN involves immune-mediated interstitial inflammation and eosinophil infiltration, whereas ATN involves direct toxic or ischaemic death of tubular epithelial cells without primary interstitial inflammation.

🔤

Word Breakdown

nephr-

=kidney (from Greek 'nephros')

-itis

=inflammation (from Greek '-itis')

Literal Meaning: Sudden inflammation of the tissue framework of the kidney

🏷️

Abbreviations

AIN=Acute Interstitial Nephritis — primary clinical abbreviation

TIN=Tubulointerstitial Nephritis — broader term often used interchangeably in acute settings

🔄

Synonyms & Variants

Acute Tubulointerstitial Nephritis›Allergic Interstitial Nephritis›

🎯

Category-Specific Context

As a Disease, acute interstitial nephritis represents a distinct clinicopathological entity within the spectrum of acute kidney injury (AKI). It is classified by its aetiology (drug-induced, infectious, autoimmune, or idiopathic) and its histopathological hallmark of interstitial inflammatory cell infiltration, which distinguishes it from pre-renal, glomerular, and vascular causes of AKI.

🏥

Clinical Context & Usage

CLINICAL SETTINGS

Nephrology WardGeneral Medicine WardIntensive Care UnitEmergency DepartmentRheumatology Clinic

USAGE & DOCUMENTATION NOTES

In clinical documentation, AIN is frequently documented as 'suspected AIN' or 'drug-induced AIN' when a clear temporal relationship exists with a new medication. Nephrology consult notes often detail the timeline of drug exposure, the presence of extra-renal allergic manifestations (rash, fever, eosinophilia), and the decision regarding empirical corticosteroids versus renal biopsy.

🔬

Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Acute interstitial nephritis is primarily an immune-mediated hypersensitivity reaction. In drug-induced cases, the drug or its metabolites act as haptens, binding to tubular basement membrane proteins and triggering a delayed-type (Type IV) T-cell-mediated hypersensitivity response, or less commonly, an antibody-mediated (Type II) response. This leads to the recruitment of inflammatory cells—predominantly T-lymphocytes and macrophages, with varying numbers of eosinophils and plasma cells—into the renal interstitium. The resulting interstitial oedema and cellular infiltration compress the peritubular capillaries and tubules, impairing tubular function and reducing the glomerular filtration rate (GFR). Infection-related AIN involves direct microbial invasion or immune complex deposition, while autoimmune AIN (e.g., in sarcoidosis or tubulointerstitial nephritis and uveitis syndrome) involves systemic granulomatous or lymphocytic infiltration.

PRIMARY CAUSES

Medications (Antibiotics, NSAIDs, PPIs)

Act as haptens triggering a T-cell-mediated hypersensitivity reaction against the tubulointerstitium.

Infections (Streptococcus, Legionella, Leptospira, viruses)

Direct bacterial invasion of the interstitium or systemic immune response causing interstitial inflammation.

Systemic Autoimmune Diseases (Sarcoidosis, SLE, Sjögren's syndrome, TINU syndrome)

Systemic granulomatous inflammation or autoantibody production leading to secondary interstitial infiltration.

Idiopathic

No identifiable drug, infectious, or systemic cause found despite extensive workup; likely an unrecognised autoimmune or environmental trigger.

💊

Drug-Induced Causes

💊 Antimicrobials (Penicillins, cephalosporins, fluoroquinolones, rifampicin, sulfonamides) ↗

Mechanism: Hapten-mediated Type IV hypersensitivity reaction targeting the tubular basement membrane.

→ Immediate discontinuation of the offending agent; monitor renal function for recovery.

💊 Non-steroidal anti-inflammatory drugs (NSAIDs) ↗

Mechanism: Delayed hypersensitivity reaction, often presenting with nephrotic-range proteinuria (minimal change disease overlap) and lacking typical allergic features like rash or eosinophilia.

→ Stop NSAID; recovery may take weeks to months; corticosteroids may be considered if no improvement.

💊 Proton pump inhibitors (PPIs) (omeprazole, pantoprazole) ↗

Mechanism: Idiosyncratic cell-mediated hypersensitivity reaction; often presents insidiously without classic allergic triad.

→ Discontinue PPI and switch to an H2-receptor antagonist if acid suppression is required.

💊 Immune checkpoint inhibitors (nivolumab, pembrolizumab, ipilimumab) ↗

Mechanism: Loss of immune tolerance leading to autoimmune-like T-cell infiltration of the renal interstitium.

→ Hold or permanently discontinue immunotherapy depending on severity; initiate systemic corticosteroids.

🌍

Epidemiology

Prevalence:Accounts for approximately 10–15% of cases of acute kidney injury (AKI) in hospitalised patients, and up to 25% of biopsy-proven AKI cases.

Age Group:Can occur at any age, but most commonly affects older adults due to higher rates of polypharmacy and increased exposure to nephrotoxic medications.

Sex Predilection:Equal

Geographic Distribution:Globally distributed; incidence correlates with regional prescribing patterns of high-risk medications (e.g., PPIs and NSAIDs) rather than geographic or ethnic factors.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 URGENT

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Unexplained AKI with recent PPI or NSAID initiation — raises suspicion for drug-induced AIN, which may lack the classic triad of fever, rash, and eosinophilia; requires prompt drug withdrawal to prevent irreversible fibrosis.
AKI accompanied by uveitis in a young female — raises concern for Tubulointerstitial Nephritis and Uveitis (TINU) syndrome, requiring ophthalmologic evaluation and systemic corticosteroids.

URGENT EVALUATION TRIGGERS

Rapidly rising serum creatinine (> 3-fold increase from baseline) indicating severe acute kidney injury.
Oliguria or anuria persisting for more than 24 hours despite fluid optimisation and withdrawal of suspected nephrotoxins.
Life-threatening electrolyte imbalances (e.g., severe hyperkalaemia) secondary to tubular dysfunction.

Contraindications & Precautions

CONTRAINDICATIONS

Systemic corticosteroids — contraindicated or require extreme caution in patients with active untreated systemic infections
uncontrolled psychosis
or severe uncontrolled diabetes mellitus.

SPECIAL PRECAUTIONS

Avoid empirical corticosteroids before ruling out active renal infection (e.g.
pyelonephritis) or confirming the diagnosis
as immunosuppression can exacerbate infectious aetiologies.
Monitor for recurrent AKI if re-challenging with a structurally related drug class
as cross-reactivity can occur.

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Chronic Kidney Disease (CKD) — persistent interstitial inflammation leading to irreversible interstitial fibrosis and tubular atrophy (IFTA).
Electrolyte disturbances — impaired tubular function causing renal potassium wasting
distal renal tubular acidosis (Type 1 RTA)
or Fanconi syndrome.
End-Stage Renal Disease (ESRD) — requiring long-term dialysis or transplantation if severe fibrosis occurs before the offending agent is removed.

🔀

Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

Acute Tubular Necrosis

Both present as intrinsic acute kidney injury; however, ATN involves muddy brown granular casts and direct tubular injury, whereas AIN involves white blood cell casts and interstitial inflammation.

Acute Glomerulonephritis

Both cause intrinsic AKI, but acute glomerulonephritis typically presents with nephritic syndrome (haematuria, red blood cell casts, hypertension), whereas AIN typically lacks significant glomerular involvement.

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Acute Tubular Necrosis (ATN)

Key Distinguishing Feature: Presence of muddy brown granular casts and epithelial cell casts in ATN, versus white blood cell casts and eosinophiluria in AIN; ATN typically follows ischaemic or toxic insults.

Atheroembolic Renal Disease

Key Distinguishing Feature: History of recent vascular procedure, presence of livedo reticularis, eosinophilia, and cholesterol clefts on biopsy distinguish atheroembolic disease from AIN.

Acute Glomerulonephritis

Key Distinguishing Feature: Dysmorphic red blood cells, red blood cell casts, and significant proteinuria point towards glomerulonephritis rather than tubulointerstitial disease.

💎

Clinical Pearls

💎

The classic triad of fever, rash, and peripheral eosinophilia is present in fewer than 10–15% of patients with drug-induced AIN. Its absence should never be used to rule out the diagnosis, especially with PPIs or NSAIDs where the presentation is often insidious.

💎

Urinary eosinophils have poor sensitivity and specificity for AIN and are no longer recommended by major guidelines as a reliable diagnostic test. White blood cell casts in the absence of urinary tract infection are a much stronger indicator of tubulointerstitial inflammation.

💎

NSAID-induced AIN frequently presents with concurrent minimal change disease, leading to nephrotic-range proteinuria—a feature uncommon in other forms of AIN. Renal biopsy is often required to confirm this overlap.

💎

Early withdrawal of the offending agent is the most critical intervention. The longer the drug is continued after the onset of AKI, the higher the risk of irreversible interstitial fibrosis and progression to chronic kidney disease.

📝

Example Usage & SOAP

CLINICAL SENTENCE

"The patient developed non-oliguric acute kidney injury two weeks after starting omeprazole, and a renal biopsy confirmed acute interstitial nephritis with prominent lymphocytic infiltration."

IN A SOAP NOTE

S: 65-year-old male presents with fatigue and decreased urine output over the past 4 days. Recently started allopurinol for gout 3 weeks ago. Reports a mild, pruritic maculopapular rash on his trunk. O: BP 135/85 mmHg, HR 78 bpm. Maculopapular rash noted on torso. Serum creatinine acutely elevated to 3.2 mg/dL from baseline 0.9 mg/dL. Urinalysis shows 2+ leukocyte esterase, 15 WBC/hpf, and WBC casts. Peripheral blood shows 8% eosinophils. A: Acute kidney injury likely secondary to allopurinol-induced acute interstitial nephritis, supported by temporal relationship, rash, eosinophilia, and WBC casts. P: 1. Discontinue allopurinol immediately. 2. Avoid further nephrotoxins. 3. Nephrology consult for consideration of renal biopsy and corticosteroid therapy. 4. Monitor daily U&Es and fluid balance.

DIFFERENTIAL DIAGNOSIS CONTEXT

Differential for intrinsic acute kidney injury: (1) Acute Interstitial Nephritis — suggested by new drug exposure, WBC casts, and eosinophilia. (2) Acute Tubular Necrosis — suggested by ischaemic event or nephrotoxin exposure, muddy brown casts. (3) Acute Glomerulonephritis — suggested by nephritic sediment, dysmorphic RBCs, RBC casts. (4) Atheroembolic disease — suggested by recent vascular procedure, livedo reticularis, eosinophilia.

📈

Prognosis

SHORT-TERM OUTCOME

If the offending drug is identified and withdrawn early, renal function typically begins to improve within days to weeks, with many patients recovering baseline GFR. Delayed withdrawal reduces the likelihood of full recovery.

LONG-TERM PROGNOSIS

The risk of incomplete recovery and progression to chronic interstitial nephritis depends on the duration of the insult and the degree of interstitial fibrosis on biopsy. Up to 40% of patients may have persistent mild-to-moderate CKD long-term.

📚

References & Coding

ICD-10 DIAGNOSTIC CODE

N10

LITERATURE CITATIONS & GUIDELINES

[1]Perazella MA, Markowitz GS. Drug-induced acute interstitial nephritis. Nat Rev Nephrol. 2010;6(8):461-470.

[2]Muriithi AK et al. Biopsy-proven acute interstitial nephritis, 1993-2011: a case series. Am J Kidney Dis. 2015;65(4):550-558.

[3]Rossi S et al. Acute interstitial nephritis. Aust Prescr. 2018;41(5):151-155.

MEDICAL DISCLAIMER — This content is intended for educational purposes and qualified healthcare professionals only. Always refer to current clinical diagnostic criteria, institutional protocols, and official guidelines. Medobo is not responsible for clinical decisions made based on this content.