From the Guidelines
A creatinine level of 104 mg/dL in urine with a normal GFR is generally considered within the normal range, as urinary creatinine concentrations typically range from 40-300 mg/dL in adults. This finding suggests that the kidneys are functioning properly in filtering waste products from the blood. Creatinine is a waste product from muscle metabolism that's filtered by the kidneys and excreted in urine. When interpreting urinary creatinine, it's essential to consider it alongside other values like serum creatinine and GFR, as recommended by the National Kidney Foundation practice guidelines for chronic kidney disease: evaluation, classification, and stratification 1.
Key Considerations
- The serum creatinine concentration is affected by factors other than GFR, such as creatinine secretion and generation and extrarenal excretion, making it a less reliable sole indicator of kidney function 1.
- Clinical laboratories should report an estimate of GFR using a prediction equation in addition to reporting the serum creatinine measurement, to provide a more accurate assessment of kidney function 1.
- The Modification of Diet in Renal Disease (MDRD) Study equation and the Cockcroft-Gault equation are recommended for estimating GFR in adults, as they take into account serum creatinine concentration and other variables such as age, sex, race, and body size 1.
Implications for Kidney Health
Given that the GFR is normal, this indicates healthy kidney function overall. Factors that can affect urinary creatinine include muscle mass, diet (particularly meat consumption), exercise, and hydration status. If concerned about kidney function, regular monitoring of both serum and urine creatinine along with GFR provides the most complete picture of kidney health. No specific action is needed for a normal urinary creatinine with normal GFR beyond routine health maintenance, as the current evidence suggests that the kidneys are functioning properly.
From the Research
Creatinine Levels and GFR
- A creatinine (Creat) level of 104mg/dL in urine is not directly addressed in the provided studies as a normal or abnormal value in relation to a normal Glomerular Filtration Rate (GFR) 2, 3, 4, 5, 6.
- However, it is established that serum creatinine levels can be influenced by various factors such as age, sex, muscle mass, and body composition, which can lead to misclassification of patients or inappropriate clinical decisions 3, 4, 6.
Estimating GFR
- GFR can be estimated using equations that include renal biomarkers like serum creatinine, but these equations have limitations and may not always accurately reflect kidney function 2, 3, 4, 6.
- The use of cystatin C as an alternative endogenous marker or performing direct measurement of GFR using an exogenous marker like iohexol can provide more accurate assessments of kidney function in certain clinical scenarios 6.
Clinical Implications
- Relying solely on serum creatinine to assess renal function can lead to underestimation of impaired kidney function, particularly in females 3.
- Clinicians should be aware of the limitations of creatinine-based GFR estimation and consider using alternative methods or markers, such as cystatin C, in certain clinical scenarios to ensure accurate assessments of kidney function 3, 4, 6.