Creatinine is a normal waste product from muscles. The loss of creatinine in the urine depends on muscle mass and therefore varies very little from day to day. However, it varies from one urination (urine evacuation) to another. Generally, the darker the urine, the more creatinine it contains and vice versa. A urine creatinine measurement taken from a single urination (single urine sample) is used to calculate the excretion of several urinary parameters without having to collect 24-hour urine (sodium, potassium, calcium, phosphorus, protein, microalbumin, etc.).
Creatinine is expressed in millimoles per litre (mmol/L). There are no normal values for this parameter. Results above 5 mmol/L are common in adults and can reach more than 25 mmol/L in highly concentrated urine. Results below 2 mmol/L most often indicate abnormal consumption of large amounts of liquid.