From the Guidelines
To determine a baseline creatinine, use the lowest stable serum creatinine value obtained during the preceding 3-6 months when the patient is at their usual state of health, and consider using a prediction equation that takes into account age, sex, race, and body size, such as the Modification of Diet in Renal Disease (MDRD) study equation, as recommended by the National Kidney Foundation 1.
Importance of Baseline Creatinine
Baseline creatinine serves as a reference point for detecting acute kidney injury, monitoring chronic kidney disease progression, and adjusting medication dosages.
- Creatinine is a breakdown product of muscle metabolism that's cleared by the kidneys, making it a reliable marker of kidney function.
- Significant deviations from baseline (typically defined as an increase of 0.3 mg/dL or 50% above baseline) may indicate kidney dysfunction.
Estimating Baseline Creatinine
If recent values aren't available, review the patient's medical records for previous creatinine measurements, focusing on periods when the patient was not acutely ill.
- For patients without prior measurements, estimate the baseline using age, sex, race, and body size considerations, though this is less accurate than using actual measurements.
Monitoring Creatinine Levels
Regular monitoring of creatinine levels is particularly important in patients with risk factors for kidney disease, including:
- Diabetes
- Hypertension
- Heart failure
- Those taking nephrotoxic medications
Clinical Considerations
Clinical laboratories should report an estimate of GFR using a prediction equation in addition to reporting the serum creatinine measurement, as this provides a more accurate assessment of kidney function 1.
- Autoanalyzer manufacturers and clinical laboratories should calibrate serum creatinine assays using an international standard to ensure accurate and reliable results 1.
From the Research
Determining Baseline Creatinine
To determine a baseline creatinine level, several methods can be used, each with its own advantages and limitations.
- The mean outpatient serum creatinine level measured 7-365 days before admission has been shown to have the highest agreement with a reference standard adjudicated by a panel of board-certified nephrologists 2.
- Using the final creatinine value from a prior inpatient admission can increase the accuracy of the most recent outpatient creatinine method 2.
- The lowest serum creatinine value within a certain time window (e.g., up to 365 days prior to ED visit) can also be used as a baseline definition, but this may result in a higher prevalence of acute kidney injury (AKI) diagnosis 3.
- Other baseline definitions, such as the most recent, mean, or median serum creatinine value, can also be used, but may affect AKI diagnosis at the emergency department 3.
Considerations for Baseline Creatinine Determination
When determining baseline creatinine levels, several factors should be considered, including:
- The time window used to select a baseline serum creatinine value, with narrower time windows (e.g., 7-365 days) generally resulting in more accurate estimates 2, 3.
- The method used to estimate baseline serum creatinine, with different methods potentially affecting AKI diagnosis and prevalence 3.
- The potential for inaccurate determination of baseline kidney function, which can misclassify AKI and affect the study of AKI-related outcomes 2, 3.
Clinical Implications
The determination of baseline creatinine levels has important clinical implications, including: