Kidney
Creatinine
What This Marker Tells Us
Creatinine is a waste product from muscle metabolism filtered by kidneys, providing the most commonly used marker of kidney function and muscle mass.
Why It Matters
Reflects kidney filtration rate since kidneys remove it from blood. Elevated creatinine indicates reduced kidney function, while context of muscle mass matters. Kidney disease progresses silently until function drops significantly, making creatinine critical for early detection. It's used to calculate eGFR, the gold standard for kidney function assessment. Maintaining kidney health prevents dialysis, cardiovascular disease, bone disease, and anemia.
How to Interpret Your Trends
Low creatinine (below 0.7 mg/dL) suggests low muscle mass, malnutrition, or liver disease. Typical creatinine (0.7-1.2 mg/dL for men, 0.5-1.0 mg/dL for women) indicates normal kidney function for given muscle mass. Elevated creatinine (above typical range) signals reduced kidney function, dehydration, or very high muscle mass. Persistently elevated levels require evaluation for kidney disease.
What Influences This Marker
Muscle mass is the primary determinant, and athletes and bodybuilders have higher baseline creatinine. Dehydration concentrates blood, temporarily raising creatinine. High protein intake, creatine supplementation, and intense exercise elevate levels. Kidney disease impairs clearance, causing persistent elevation. Adequate hydration and understanding your muscle mass baseline enables proper interpretation.
How Your Team Uses It
Your coach uses creatinine to monitor kidney function, accounting for your muscle mass and training. Elevated creatinine prompts investigation of hydration, supplement use, and kidney health. It's combined with age, sex, and race to calculate eGFR. Changes guide adjustments to protein intake, hydration protocols, and supplement recommendations.
Related Signals We Also Review
eGFR, BUN, BUN/creatinine ratio, electrolytes, urinalysis, blood pressure, and glucose complete the kidney function assessment.