From the Guidelines
Low creatinine levels can be clinically significant and may indicate decreased muscle mass, malnutrition, or liver disease, and can mask kidney dysfunction in patients with decreased muscle mass. When evaluating low creatinine levels, it is essential to consider the patient's overall clinical context, including their muscle mass, nutritional status, and liver function, as emphasized by the British Association of Dermatologists guidelines for the safe and effective prescribing of oral ciclosporin in dermatology 2018 1. The guidelines highlight that serum creatinine levels are related to muscle mass, and individuals with large muscle mass and healthy kidneys may have higher serum creatinine levels, while those with low muscle mass may develop significant nephrotoxicity even with normal serum creatinine levels. According to the National Kidney Foundation practice guidelines for chronic kidney disease, serum creatinine concentration should not be used as the sole means to assess kidney function, as it can be affected by factors such as creatinine secretion and generation, and extrarenal excretion 1. Additionally, the clinical practice guidelines for nutrition in chronic renal failure by the National Kidney Foundation suggest that a low serum creatinine concentration can indicate protein-energy malnutrition and wasting of skeletal muscle, and is associated with increased mortality rates 1. Key points to consider when evaluating low creatinine levels include:
- Decreased muscle mass, which can occur in elderly patients, those with muscle-wasting diseases, or individuals with malnutrition
- Malnutrition, which can be indicated by a low creatinine index and low serum creatinine concentration
- Liver disease, which can affect creatine production and lead to low creatinine levels
- The need for alternative markers of kidney function, such as cystatin C, to accurately assess kidney function in patients with decreased muscle mass. Regular monitoring and evaluation of nutritional status, muscle health, and liver function are crucial in patients with low creatinine levels to detect changes that may indicate worsening of the underlying condition.
From the Research
Clinical Significance of Low Creatinine
- Low creatinine levels can be an indicator of low muscle mass, which is a significant predictor of morbidity and mortality in various clinical settings 2.
- Serum creatinine is closely related to muscle mass, and its levels can be influenced by factors such as age, sex, and muscle wasting 3, 4, 5.
- In patients with chronic kidney disease, serum creatinine can serve as a reliable biomarker of skeletal muscle mass if adjusted for kidney function and dietary meat intake 5.
Limitations of Serum Creatinine as a Marker of Renal Function
- Serum creatinine has limitations as a marker of renal function due to its tubular secretion and influence of muscular mass or protein intake on its concentration 6.
- The relationship between serum creatinine and glomerular filtration rate is hyperbolic, making it less precise in low or normal-low creatinine levels 6.
- Low muscle mass can cause overestimation of single measurements of estimated glomerular filtration rate (eGFR) based on creatinine, and muscle wasting can cause spurious overestimation of repeatedly measured eGFR 3.
Alternative Markers of Renal Function
- Cystatin C is a muscle mass-independent marker that can be used as a more reliable alternative to creatinine for estimating renal function 3, 4.
- The use of cystatin C can help eliminate the negative consequences of current race-based approaches to estimating renal function 3.
- Studies have shown that cystatin C is not associated with muscle mass, making it a more accurate marker of renal function than creatinine 4.