From the Guidelines
Creatinine and estimated glomerular filtration rate (eGFR) are imperfect measures of baseline renal function, and their accuracy can be improved by considering additional factors such as cystatin C measurements. When assessing baseline renal function, it is essential to consider the limitations of serum creatinine and eGFR. Serum creatinine can be affected by muscle mass, diet, medications, and age, making it a less reliable marker in certain populations, such as the elderly or those with muscle wasting 1. eGFR calculations, which account for factors like age, sex, race, and body size, can provide a more accurate estimate of renal function, but they also have limitations, particularly at higher values (>60 mL/min/1.73m²) where they become less precise 1.
Limitations of Creatinine and eGFR
Some of the key limitations of creatinine and eGFR include:
- Muscle mass: Creatinine is affected by muscle mass, which can lead to inaccurate estimates of renal function in individuals with high or low muscle mass 1.
- Diet: Certain dietary patterns can also impact creatinine levels, further limiting its accuracy 1.
- Medications: Certain medications, such as trimethoprim, can cause spuriously high serum creatinine levels by blocking its tubular secretion 1.
- Age: Creatinine levels can be affected by age, making it a less reliable marker in elderly patients 1.
Role of Cystatin C
Recent studies suggest that incorporating cystatin C measurements into the assessment of renal function can improve accuracy, particularly in the diagnosis and staging of chronic kidney disease (CKD) 1. Cystatin C has been shown to strengthen the association between eGFR and cardiovascular events, kidney failure, and death, and it does not require the incorporation of a race coefficient, making it a valuable addition to CKD diagnosis and treatment initiatives 1.
Clinical Implications
In clinical practice, tracking trends in creatinine and eGFR over time, and considering additional factors such as cystatin C measurements, can provide more valuable information about kidney function than isolated measurements. This approach can help identify progressive decline or improvement in renal function, allowing for earlier intervention and more effective management of kidney disease 1.
From the Research
Limitations of Creatinine and eGFR as Measures of Baseline Renal Function
- Serum creatinine is the most widely used functional biomarker of the kidney, but its use is associated with substantial shortcomings 2
- eGFRcr may be inaccurate in people with variation in muscle mass or diet, and eGFRcys is not more accurate than eGFRcr 3
- Measured GFR is not practical and is susceptible to error due to variation in clearance methods and in the behavior of exogenous filtration markers 3
Alternative Measures of Renal Function
- Cystatin C-based equations can be used as confirmatory tests for a more accurate GFR assessment 4
- Urinary or plasma clearance of exogenous filtration markers, or urinary clearance of creatinine can also be used as confirmatory tests 4
- New creatinine- and cystatin C-based equations to estimate GFR without race have been developed, which may be more accurate than traditional equations 5
Clinical Practice and Renal Function Assessment
- Assessment of GFR is fundamental to clinical practice, public health, and research 4
- GFR is used to diagnose, stage, and manage chronic kidney disease (CKD); ascertain the prognosis for chronic kidney disease-related events and mortality; and determine drug dosages 4
- Despite the actual recommendations, the serum creatinine level still remains the most popular routine parameter used to evaluate renal function 6