From the Guidelines
A creatinine level of 104 in urine is not clinically meaningful on its own, as urinary creatinine concentration varies widely based on hydration status and urine concentration. Urinary creatinine is typically used as a reference value to standardize the measurement of other substances in urine, such as protein or microalbumin, rather than being interpreted in isolation. To properly assess kidney function, a serum creatinine test should be performed, along with calculation of estimated glomerular filtration rate (eGFR) 1. If you're concerned about kidney function, request a comprehensive metabolic panel that includes serum creatinine, BUN, and electrolytes. For monitoring kidney health, the protein-to-creatinine ratio or albumin-to-creatinine ratio in urine provides more valuable information than urinary creatinine alone. Creatinine is a waste product of muscle metabolism that's filtered by the kidneys, which is why it serves as a useful marker for kidney function when measured in blood, not in isolated urine measurements.
Key Points to Consider
- Urinary creatinine concentration is not a reliable indicator of kidney function due to its variability based on hydration status and urine concentration 1.
- Serum creatinine test and estimated glomerular filtration rate (eGFR) calculation are essential for assessing kidney function 1.
- Comprehensive metabolic panel, including serum creatinine, BUN, and electrolytes, provides a more accurate picture of kidney health.
- Protein-to-creatinine ratio or albumin-to-creatinine ratio in urine is more informative for monitoring kidney health than urinary creatinine alone.
Recommendations
- Do not rely solely on urinary creatinine concentration to assess kidney function.
- Use serum creatinine test and eGFR calculation to evaluate kidney function.
- Request a comprehensive metabolic panel to assess kidney health.
- Monitor kidney health using protein-to-creatinine ratio or albumin-to-creatinine ratio in urine.
From the Research
Impaired Renal Function Indicated by Elevated Creatinine Level
- Elevated creatinine level in urine, such as 104, can indicate impaired renal function 2, 3
- Serum creatinine is a commonly used index of renal function, but it has its limitations, as patients can have significantly decreased glomerular filtration rates (GFR) with normal range serum creatinine values 2
- Creatinine clearance (CrCl) is a more accurate measure of renal function, and it can be calculated using various formulas, such as the urinary CrCl formula, Cockcroft-Gault, MDRD, and body surface formula 2
Comparison of Biomarkers for Renal Function
- Serum cystatin C has been established as an early and accurate biomarker of chronic kidney disease (CKD) that is particularly helpful in patients for whom creatinine is an inadequate marker 4
- Plasma and urine biomarkers, such as kidney injury molecule-1, monocyte chemoattractant protein-1, and fibroblast growth factor-23, can improve our ability to prognosticate CKD progression and may improve our understanding of CKD pathophysiology 5
- Urine creatinine excretion is a reliable approximation of muscle mass, and changes in urine creatinine can predict clinical outcomes in persons with CKD 3
Clinical Outcomes and Renal Function
- Lower urine creatinine excretion predicts greater risk of kidney failure and patient mortality in persons with CKD stages 3 and 4 3
- Severity of acute kidney injury (AKI) is determined by the magnitude of increase in serum creatinine level or decrease in urine output, and patients with both oliguria and azotemia are more likely to have worse disease 6
- Duration of AKI is a significant predictor of long-term outcomes, irrespective of severity, and short- and long-term risk of death or renal replacement therapy is greatest when patients meet both the serum creatinine level and urine output criteria for AKI 6