Glomerular filtration rate (GFR) serves as a marker for various renal functions. Different formulas are available to calculate an estimated GFR (eGFR), which are commonly based on serum creatinine, age, and sex. However, the eGFR merely reflects GFR under specific conditions. Due to the multitude of functions of the kidney, it is not possible to capture all aspects in one value. To diagnose renal diseases comprehensively, not only eGFR but also urine analysis and clinical context should be considered. Interpretation of eGFR for renal function monitoring requires careful consideration of factors such as (blood pressure) medication, diabetes, obesity, and pregnancy. Combining various laboratory parameters with a patient's clinical context provides an overview of the different functions of the kidney and its consequences for the patient.