Creatinine is the end-product of muscle catabolism of creatine. In humans, creatinine production is relatively stable, but mainly depends on muscles mass. Consequently, any physiological changes in muscle mass will cause a variation in the creatinine pool independently of GFR changes. Creatinine is freely filtered by the glomerulus at a constant rate with 10% to 40% secreted by the tubules ¹.

Creatinine measurements are useful in the diagnosis and monitoring of diabetic nephropathy, the leading cause of kidney disease in patients commencing renal replacement therapy, affecting 40% of diabetics (type 1 and type 2) ⁵. The RENAAL (Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan) study risk score for end-stage renal disease (ESRD) emphasizes the importance of the identification of elevated SCr, alongside other renal markers, in the prediction of end-stage renal disease (ESRD) development in patients with type 2 diabetes mellitus (T2DM) and nephropathy ⁶.

Acute kidney injury (AKI) is a common complication in COVID-19 patients ⁷. The analysis of creatinine in COVID-19 patients on hospital admission and after 2 to 4 days highlighted impaired renal function and is the leading cause of death in these patients ⁸. The National Institute of Care Excellence (NICE), have set out four guidelines for acute kidney injury in hospitalised suspected or confirmed COVID-19 patients and highlights the importance of creatinine testing ⁹.