Renal · Year 2 · from Renal
Case 3: Contrast-Induced Nephropathy
Patient Presentation
A 64-year-old male with type 2 diabetes and chronic kidney disease (baseline creatinine 1.8 mg/dL, eGFR 38) undergoes cardiac catheterization for unstable angina. He returns 48 hours later with decreased urine output.
History of Present Illness
- Cardiac catheterization performed 2 days ago with 150 mL of iodinated contrast
- Received inadequate pre-procedure hydration
- Decreased urine output since the procedure
- No chest pain
- Taking metformin (was not held)
Physical Examination
- Blood pressure: 142/88 mmHg
- Heart rate: 82 bpm
- No peripheral edema
- Lungs clear
- Cardiac stent in place with good result
Workup
Laboratory Studies:
- Baseline creatinine: 1.8 mg/dL
- Current creatinine (48 hours post-procedure): 3.2 mg/dL
- BUN: 48 mg/dL
- Potassium: 5.1 mEq/L
- Urinalysis: 1+ protein, rare muddy brown casts
- FENa: 2.4%
Diagnosis
Contrast-Induced Nephropathy (Contrast-Induced Acute Kidney Injury)
Discussion
This case relates to GFR measurement and clinical applications:
- Creatinine as GFR Marker: The lecture explains that creatinine clearance slightly overestimates GFR due to tubular secretion. The rise in creatinine 24-48 hours post-contrast is characteristic of contrast nephropathy.
- Risk Factors: Pre-existing CKD (especially GFR <45) and diabetes are the strongest risk factors, as discussed in clinical applications.
- Mechanism: Contrast causes both afferent vasoconstriction (reducing PGC) and direct tubular toxicity, transitioning from prerenal to intrinsic injury.
Prevention (Should Have Been Done)
- IV saline hydration before and after procedure
- Hold metformin (lactic acidosis risk with AKI)
- Minimize contrast volume
- Consider alternatives to contrast (CO2 angiography)
- Avoid concurrent nephrotoxins (NSAIDs)
Treatment
- Supportive care with IV fluids
- Hold metformin until creatinine stabilizes
- Monitor for recovery (typically peaks at 3-5 days, resolves by 7-14 days)
- Patient's creatinine peaked at 3.8 mg/dL on day 4, then gradually improved to 2.2 mg/dL by day 10
Clinical Pearl
Contrast nephropathy follows a predictable time course: creatinine begins rising within 24-48 hours, peaks at 3-5 days, and usually resolves within 7-14 days. Patients with pre-existing CKD may not return to baseline.
Image Reference
For visual reference of concepts in this lecture, see:
- Radiopaedia: Renal artery stenosis - Doppler and angiographic images
- Wikimedia Commons: Glomerulus - Histology images showing filtration structures
- Radiopaedia: Contrast-induced nephropathy - Clinical information and imaging
Learning Points
- Autoregulation Limits: Autoregulation maintains stable GFR over MAP 80-180 mmHg. Below this range, GFR falls proportionally with blood pressure.
- NSAIDs and Prostaglandins: Prostaglandins provide protective afferent dilation during states of reduced renal perfusion; NSAIDs remove this protection.
- ACE Inhibitors and Efferent Tone: ACE inhibitors dilate the efferent arteriole, reducing PGC and GFR. This is beneficial for proteinuria reduction but dangerous in bilateral renal artery stenosis.
- Creatinine Kinetics: Serum creatinine is a lagging indicator - it reflects GFR changes from the previous days, not real-time kidney function.
- FENa Interpretation: FENa <1% suggests prerenal etiology with intact tubular function; FENa >2% suggests intrinsic renal injury.