From the Guidelines
Creatinine is a good marker for kidney function because it is a waste product produced at a relatively constant rate by muscle metabolism and is primarily eliminated by the kidneys through glomerular filtration. This relationship between creatinine and kidney function is predictable enough that equations using creatinine levels can estimate glomerular filtration rate (GFR), the gold standard measure of kidney function 1. The fact that creatinine is freely filtered by the kidneys but not reabsorbed or significantly secreted makes its blood levels directly reflect how well the kidneys are filtering waste products.
When kidney function declines, creatinine accumulates in the blood, making elevated serum creatinine levels a reliable indicator of decreased kidney function. However, it's essential to consider that creatinine levels can be influenced by factors like muscle mass, diet, and certain medications, so interpretation should take these variables into account 1. Despite these limitations, creatinine remains the most practical and useful clinical marker for assessing and monitoring kidney function in everyday practice.
Some key points to consider when using creatinine as a marker for kidney function include:
- The serum creatinine concentration is affected by factors other than GFR, such as creatinine secretion and generation and extrarenal excretion 1.
- Clinical laboratories should report an estimate of GFR using a prediction equation in addition to reporting the serum creatinine measurement 1.
- The relationship between creatinine and kidney function is predictable enough that equations using creatinine levels can estimate GFR, which is a critical element in the strategy for improving care of patients with chronic kidney disease 1.
- A reduction in GFR and an increase in cardiovascular risk may also be inferred from the increased serum levels of cystatin C 1.
Overall, creatinine is a valuable marker for kidney function, and its measurement, in combination with other factors, can provide a comprehensive assessment of kidney health and guide clinical decision-making 1.
From the Research
Why Creatinine is a Good Marker for Kidney Function
- Creatinine is the most widely used functional biomarker of the kidney, as stated in the study 2.
- It is used to estimate static kidney function accurately and detect changes in kidney function in a timely fashion 2.
- Serum creatinine concentration is a reliable indicator of kidney function, with higher concentrations indicating poorer kidney function 3.
- The use of creatinine as a marker of kidney function is associated with substantial shortcomings, but understanding these shortcomings is critical for accurate interpretation of creatinine values 2.
Advantages of Using Creatinine as a Marker
- Creatinine is easily measurable in the blood and urine, making it a convenient marker for kidney function 2.
- It is correlated with estimated glomerular filtration rate (eGFR), which is a key indicator of kidney function 4.
- Creatinine levels can be used to assess the risk of post-contrast acute kidney injury following contrast-enhanced computed tomography imaging 5.
Limitations of Using Creatinine as a Marker
- Serum creatinine concentration can be influenced by factors such as muscle mass, age, and sex, which can affect its accuracy as a marker of kidney function 2.
- There are alternative functional biomarkers of the kidney, such as urine protein, that can be used in certain situations 3.
- The use of point-of-care creatinine tests can be limited by factors such as the accuracy of the device and the presence of risk factors for kidney disease 5.