Contrast-Induced Nephropathy
Nephrology
Illness script · Nephrology
Contrast-Induced Nephropathy
Acute kidney injury defined as serum creatinine rise ≥0.5 mg/dL or ≥25% above baseline within 48–72 hours of intravascular iodinated contrast administration.
This illness script for Contrast-Induced Nephropathy covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Pre-existing CKD — single greatest risk factor (GFR <60 significantly increases risk)
- Diabetic nephropathy — DM alone with normal GFR is lower risk
- Volume depletion / hypotension / heart failure (low renal perfusion)
- Large contrast volume or high-osmolality agent; intra-arterial > IV route
- Concurrent nephrotoxins: NSAIDs, aminoglycosides, ACEi/ARB in acute setting
- Advanced age, hypertension, multiple myeloma
02
Presentation
- Typically asymptomatic — detected on routine post-procedure labs
- Creatinine rise begins 24–48 h post-contrast, peaks at 3–5 days
- Oliguria may occur in severe cases
- Urinalysis: muddy brown granular casts (ATN-like pattern)
- FENa may be <1% early (vasoconstriction phase) despite intrinsic injury
- Usually resolves within 7–14 days; persistent injury suggests alternative etiology
03
Pathophysiology
- Direct tubular epithelial toxicity → reactive oxygen species → oxidative injury
- Contrast triggers renal vasoconstriction → outer medullary ischemia (most vulnerable zone)
- Increased urine viscosity → tubular obstruction and back-pressure on glomeruli
- Net result mirrors acute tubular necrosis (ATN) pattern
04
Diagnostics
- Monitor BMP at 48–72 h post-contrast in at-risk patients — key diagnostic window
- Urinalysis: granular/muddy brown casts support tubular injury
- FENa: <1% early (vasoconstriction) → can shift >1% as tubules lose concentrating ability
- Renal ultrasound to exclude obstruction if creatinine does not trend down
- Diagnosis of exclusion — rule out volume depletion, obstruction, cholesterol emboli
05
Management
- PREVENTION is the primary strategy — most effective intervention
- IV isotonic saline (1 mL/kg/h) 3–6 h pre- and post-procedure — most evidence-based
- Use minimum volume of iso-osmolar (iodixanol) or low-osmolar contrast
- Hold metformin 48 h after contrast in high-risk patients (lactic acidosis risk if AKI develops)
- Hold NSAIDs and other nephrotoxins peri-procedure
- N-acetylcysteine (NAC): controversial; limited proven benefit but low-risk to give
- Supportive care if AKI occurs; dialysis reserved for severe/refractory cases
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Prerenal AKI
Prerenal AKI responds rapidly to fluid resuscitation and lacks the time-locked association with contrast exposure.
ATN from other causes (e.g., sepsis, aminoglycosides)
Other ATN etiologies have a different temporal trigger; CIN onset is strictly tied to contrast administration within 24–48 h.
Cholesterol embolism syndrome
Cholesterol emboli also follow angiography but present days to weeks later with livedo reticularis, eosinophilia, and digital ischemia.
Allergic interstitial nephritis
AIN features eosinophiluria, rash, fever, and eosinophilia — absent in CIN, which lacks systemic allergic signs.
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.