Contrast-induced nephropathy (CIN)

Contrast-induced nephropathy (CIN), also referred to as contrast-induced acute kidney injury (CI-AKI), is an acute deterioration in renal function that occurs following exposure to iodinated contrast media used during diagnostic and interventional procedures. Common procedures associated with CIN include computed tomography (CT) scans with contrast, coronary angiography, peripheral angiography, and other contrast-enhanced radiological studies. Although magnetic resonance imaging (MRI) commonly uses gadolinium-based contrast agents rather than iodinated contrast, contrast-associated renal injury may also occur in susceptible patients. CIN is typically characterized by a transient rise in serum creatinine occurring within 24–48 hours after contrast exposure, followed by recovery of renal function within 3–7 days in most patients.

CIN remains one of the most common causes of hospital-acquired acute kidney injury and is particularly important in patients with pre-existing chronic kidney disease and other risk factors.

Epidemiology

The incidence of CIN varies according to patient risk factors and the type of procedure performed. In the general population, the incidence is low; however, it may exceed 20–30% among high-risk patients, particularly those with chronic kidney disease, diabetes mellitus, heart failure, or advanced age. The widespread use of low-osmolar and iso-osmolar contrast media has significantly reduced the incidence of CIN.

Risk factors

Patient-related risk factors

• Pre-existing chronic kidney disease

• Diabetes mellitus, especially with diabetic nephropathy

• Congestive heart failure

• Advanced age

• Hypovolaemia or dehydration

• Hypotension

• Anaemia

• Sepsis

• Liver disease

• Multiple myeloma

• Renal transplant recipients

Procedure-related risk factors

• High volume of contrast media

• Repeated contrast exposure within a short period

• Use of high-osmolar contrast agents

• Intra-arterial contrast administration

• Emergency angiographic procedures

Medication-related risk factors

• Non-steroidal anti-inflammatory drugs (NSAIDs)

• Nephrotoxic antibiotics

• Diuretics causing volume depletion

• Other nephrotoxic medications

Pathophysiology

The pathogenesis of CIN is multifactorial and involves renal vasoconstriction, medullary hypoxia, direct tubular toxicity, and oxidative stress.

Following administration of contrast media, renal blood flow decreases due to vasoconstriction of the renal microcirculation. Reduced blood flow particularly affects the renal medulla, which is already vulnerable to hypoxia. Contrast agents may also exert direct toxic effects on tubular epithelial cells, resulting in acute tubular injury or acute tubular necrosis.

Generation of reactive oxygen species further contributes to cellular injury. These mechanisms collectively lead to a transient decline in glomerular filtration rate (GFR), manifested clinically by a rise in serum creatinine.

Clinical presentation

Most patients are asymptomatic and the diagnosis is often established through laboratory monitoring following contrast exposure. Clinical manifestations generally appear within the first 24–48 hours after administration of contrast media.

Symptoms

• Usually asymptomatic

• Reduced urine output in severe cases

• Generalized weakness

• Nausea

• Loss of appetite

• Symptoms related to fluid overload in severe cases

• Symptoms associated with electrolyte disturbances

Clinical signs

• Normal urine output (non-oliguric acute kidney injury) in most patients

• Oliguria in severe cases

• Signs of volume overload, including peripheral oedema

• Hypertension due to fluid retention

• Signs of hyperkalaemia in severe cases

• Features of uraemia in advanced acute kidney injury

Diagnostic criteria

CIN is generally diagnosed when:

• Serum creatinine increases by ≥0.3 mg/dL (≥26.5 μmol/L) within 48 hours after contrast exposure; or

• Serum creatinine increases to ≥1.5 times baseline within 7 days after exposure; and

• No alternative cause of acute kidney injury is identified.

A temporal relationship between contrast administration and deterioration in renal function supports the diagnosis.

Investigations

Baseline investigations

All patients scheduled for contrast-enhanced procedures should undergo:

• Serum creatinine measurement before contrast administration

• Estimation of glomerular filtration rate (eGFR)

• Assessment of risk factors for acute kidney injury

Follow-up investigations

• Serum creatinine at 24–48 hours after contrast exposure

• Repeat renal function tests if abnormalities are detected

Investigations for patients with elevated creatinine

• Serial serum creatinine measurements for up to 7 days

• Serum potassium

• Serum sodium

• Serum phosphate

• Serum calcium

• Serum bicarbonate

• Urinalysis

• Urine microscopy

• Kidney, ureter, and bladder (KUB) ultrasound

Additional findings

Urinalysis may reveal:

• Granular casts

• Tubular epithelial cells

• Sediment suggestive of acute tubular necrosis

Laboratory abnormalities may include:

• Hyperkalaemia

• Metabolic acidosis

• Hyperphosphataemia

• Elevated serum creatinine

Management

Management focuses on prevention, early identification, supportive care, correction of electrolyte abnormalities, and treatment of complications.

Non-pharmacological treatment

Prevention strategies

• Identify high-risk patients before contrast administration

• Assess baseline renal function in all patients undergoing contrast studies

• Avoid unnecessary contrast-enhanced procedures

• Encourage adequate hydration before and after contrast administration

• Discontinue NSAIDs 24–48 hours before contrast exposure where clinically feasible

• Minimize exposure to other nephrotoxic agents

• Use the lowest effective volume of contrast media, preferably less than 125 mL where possible

• Use low-osmolar contrast media such as iohexol or ioversol

• Use iso-osmolar contrast media such as iodixanol when appropriate

• Avoid repeated contrast administration within a short interval

Supportive care

• Monitor urine output

• Monitor renal function and electrolytes

• Correct fluid and electrolyte disturbances

• Manage complications promptly

Pharmacological treatment

Intravenous hydration

Intravenous isotonic saline remains the most effective pharmacological preventive measure when no contraindication exists.

Outpatients

• Sodium chloride 0.9% intravenous infusion 3 mL/kg over 1 hour before the procedure, followed by 1–1.5 mL/kg/hour during the procedure and for 4–6 hours after the procedure, ensuring administration of at least 6 mL/kg after the procedure.

Inpatients

• Sodium chloride 0.9% intravenous infusion 1 mL/kg/hour for 6–12 hours before the procedure, continued during the procedure and for 6–12 hours after the procedure.

Management of complications

• Hyperkalaemia should be treated according to standard hyperkalaemia management protocols.

• Metabolic acidosis should be corrected when clinically significant.

• Fluid overload should be managed appropriately according to clinical status.

Management according to underlying cause

Patients with chronic kidney disease

• Close monitoring of renal function

• Minimize contrast volume

• Use low- or iso-osmolar contrast agents

• Aggressive hydration where appropriate

Patients with diabetes mellitus

• Optimize glycaemic control

• Assess renal function before and after contrast administration

• Ensure adequate hydration

Patients with heart failure

• Balance hydration carefully to avoid fluid overload

• Monitor for worsening cardiac status

Referral

Refer the patient to a nephrologist if:

• Acute kidney injury is severe or progressive

• Serum creatinine continues to rise beyond 7 days

• Significant electrolyte abnormalities develop

• Persistent oliguria occurs

• Dialysis is being considered

• Underlying chronic kidney disease is advanced

• The diagnosis is uncertain

Complications

• Acute tubular necrosis

• Severe acute kidney injury

• Hyperkalaemia

• Metabolic acidosis

• Fluid overload

• Pulmonary oedema

• Requirement for renal replacement therapy

• Prolonged hospitalization

• Increased cardiovascular morbidity

• Death in severe cases

Prognosis

The prognosis is generally favourable, with most patients experiencing recovery of renal function within 3–7 days. Patients with pre-existing chronic kidney disease, diabetes mellitus, or severe acute kidney injury are at greater risk of incomplete recovery and progression to chronic kidney disease. Severe cases may require temporary renal replacement therapy.

Prevention

• Screen all patients for risk factors before contrast administration.

• Measure baseline serum creatinine and estimate eGFR before contrast studies.

• Ensure adequate hydration before and after contrast exposure.

• Use the lowest possible dose of contrast media.

• Prefer low-osmolar or iso-osmolar contrast agents.

• Avoid nephrotoxic medications when possible.

• Monitor renal function 24–48 hours after contrast administration in at-risk patients.

• Avoid repeated contrast exposure within short intervals.

• Educate healthcare providers regarding risk assessment and preventive strategies.