From the Guidelines
Creatine and creatinine are distinct substances measured in blood tests, with creatinine being the more clinically significant marker, as it is used to assess kidney function and potential kidney problems, as stated in the guidelines by the National Kidney Foundation 1.
Key Differences
- Creatine is a natural compound stored in muscles that provides energy for physical activity.
- Creatinine is the waste product of creatine metabolism that's filtered by the kidneys and excreted in urine.
Clinical Significance
- Creatinine levels are routinely measured to assess kidney function, with elevated levels indicating potential kidney problems.
- Normal creatinine ranges are typically 0.7-1.3 mg/dL for men and 0.6-1.1 mg/dL for women, though these vary by laboratory.
- Creatinine is particularly valuable because it's produced at a relatively constant rate, making it a reliable indicator of kidney filtration capacity.
Estimating Kidney Function
- Doctors often use creatinine values to calculate estimated glomerular filtration rate (eGFR), providing a more precise assessment of kidney function.
- Clinical laboratories should report an estimate of GFR using a prediction equation in addition to reporting the serum creatinine measurement, as recommended by the National Kidney Foundation 1.
Important Considerations
- While creatine supplements are popular among athletes and can temporarily raise blood creatinine without indicating kidney disease, it's essential to inform your healthcare provider about supplement use when interpreting test results.
- The guidelines recommend obtaining 24-hour urine collections only for special clinical circumstances, as measurement of creatinine clearance by using timed urine collections does not provide more accurate estimates of GFR than do prediction equations 1.
From the Research
Difference between Creatine and Creatinine
- Creatine and creatinine are two distinct substances that are often confused with each other due to their similar names.
- Creatine is a substance found in muscle cells, while creatinine is a waste product that is produced by the breakdown of creatine in the muscles and filtered out of the blood by the kidneys.
Significance of Creatinine in Blood Test
- Creatinine levels in the blood are used to estimate glomerular filtration rate (GFR), which is a measure of kidney function 2, 3, 4.
- Elevated creatinine levels in the blood can indicate impaired kidney function or kidney disease 4, 5.
- The relationship between serum creatinine and estimated GFR is significant in patients with chronic kidney disease, as it can help identify those at risk of complications related to kidney disease 4.
Estimation of GFR using Creatinine
- The Modification of Diet in Renal Disease (MDRD) equation is commonly used to estimate GFR from serum creatinine measurements, but it has been shown to underestimate GFR in healthy individuals 2.
- A new equation that uses both patients with chronic kidney disease and healthy individuals may be more accurate in estimating GFR 2.
- The use of race in GFR estimation has limitations, and alternative methods that do not require the use of demographic characteristics are being developed 6.
Clinical Application of Creatinine
- Serum creatinine is the most widely used functional biomarker of the kidney, but its use is associated with substantial shortcomings 5.
- Understanding the pathways involved in creatinine generation and metabolism, as well as the techniques involved in measuring creatinine concentrations, is critical in allowing accurate interpretation of creatinine values and translating them into changes in kidney function 5.