← Back to CalculatorsHome
Contrast Safety
Demonstration data

eGFR Calculator (Contrast Safety)

Calculate estimated Glomerular Filtration Rate to assess renal function before IV contrast administration. Prevent contrast-induced nephropathy.

This calculator estimates glomerular filtration rate (eGFR) from serum creatinine using the CKD-EPI equation to stratify renal function prior to intravascular iodinated (or gadolinium) contrast administration. Renal function is the principal determinant of the risk of contrast-associated acute kidney injury and, for gadolinium agents, nephrogenic systemic fibrosis. eGFR guides decisions on contrast justification, prophylactic hydration, and agent selection.

🧮 Interactive Calculator

📐 Formula

CKD-EPI equation: eGFR = 141 × min(SCr/κ, 1)^α × max(SCr/κ, 1)^-1.209 × 0.993^Age × [1.018 if female] × [1.159 if black]

Reference: CKD-EPI 2021

When to Use

  • Screening renal function before elective contrast-enhanced CT, angiography, or interventional procedures
  • Deciding whether hydration prophylaxis or dose reduction is warranted before iodinated contrast
  • Selecting the safest gadolinium agent class and dose before contrast-enhanced MRI
  • Risk-stratifying patients with diabetes, hypertension, or known chronic kidney disease
  • Determining the need for nephrology consultation or post-contrast renal monitoring

How It Works

  • The CKD-EPI equation estimates GFR (mL/min/1.73 m2) from standardised serum creatinine (SCr, mg/dL), age, and sex, with a historical race coefficient now increasingly removed
  • eGFR = 141 × min(SCr/κ, 1)^α × max(SCr/κ, 1)^-1.209 × 0.993^Age × 1.018 (if female) × 1.159 (if Black, in the original 2009 equation)
  • κ is 0.7 for females and 0.9 for males; α is -0.329 for females and -0.411 for males; these sex-specific constants linearise the creatinine relationship
  • Serum creatinine must be an IDMS-traceable, standardised measurement in mg/dL (multiply µmol/L by 0.0113 to convert)
  • The result is normalised to a body surface area of 1.73 m2 and assumes stable (steady-state) creatinine, so it is invalid during acute kidney injury
  • Major guidelines (NKF-ASN 2021) now recommend the race-free CKD-EPI 2021 refit; the race multiplier in the classic formula is being retired

Interpreting the Result

  • eGFR >=60 mL/min/1.73 m2: normal to mildly reduced function; standard intravenous iodinated contrast is generally considered low risk in most guidelines
  • eGFR 30-59: moderately reduced (CKD stage 3); many protocols consider IV contrast with consideration of hydration, though recent evidence (ACR-NKF 2020) indicates low risk down to ~30 for IV administration
  • eGFR <30 (CKD stage 4-5): the threshold below which contrast-associated AKI risk and, for gadolinium, nephrogenic systemic fibrosis risk are highest; use only if benefit outweighs risk, prefer group II gadolinium agents at lowest dose, and apply prophylaxis
  • Intra-arterial first-pass renal exposure carries higher risk than IV administration at any given eGFR
  • A single eGFR is a snapshot; a falling trend or acute illness reclassifies the patient upward in risk regardless of the absolute value

Limitations & Pitfalls

  • Invalid in acute kidney injury or any non-steady-state creatinine, where eGFR lags true GFR
  • Creatinine is affected by muscle mass, so eGFR is unreliable in amputees, the frail elderly, bodybuilders, malnourished, and pregnant patients
  • Extremes of body habitus distort the 1.73 m2 normalisation; absolute GFR (deindexed) may be needed for drug or contrast dosing
  • The race coefficient in the 2009 equation is now considered scientifically and ethically problematic; use the 2021 race-free refit where available
  • Certain drugs (trimethoprim, cimetidine) raise creatinine without lowering true GFR, causing spurious eGFR reduction
  • Point-of-care creatinine assays may not be IDMS-standardised, introducing bias
  • eGFR does not by itself capture the full contrast-AKI risk profile (volume status, nephrotoxins, heart failure, contrast dose/route)

References

  • Levey AS et al. A New Equation to Estimate Glomerular Filtration Rate (CKD-EPI). Ann Intern Med 2009
  • Inker LA et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race (CKD-EPI 2021). N Engl J Med 2021
  • ACR Manual on Contrast Media (current edition) - sections on Contrast-Associated Acute Kidney Injury and Nephrogenic Systemic Fibrosis
  • ACR-National Kidney Foundation Consensus Statement on the Use of Intravenous Iodinated Contrast Media in Patients with Kidney Disease. Radiology 2020
  • KDIGO Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease (2012)

⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.