The importance of serum creatinine in the diagnosis of chronic kidney disease

Chronic kidney disease (CKD) is a recently recognized public health problem, with an increasing number of end stage renal disease patients, requiring dialysis or transplantation. In 2002, the Kidney Disease Outcomes Quality Initiative recommended the use of an estimated glomerular filtration rate (eGFR) to detect early kidney disease. For calculating eGFR in adults, the National Kidney Disease Education Programme (NKDEP) recommends using either of 2 versions of the 4-variable Modification of Diet in Renal Disease (MDRD) Study equation. In this equation, serum creatinine (Scr) is the most important variable. The equation also depends on age, sex and race. Scr concentration has no clinical significance other than to serve as a surrogate marker of kidney function, and its measurement has been accepted as the best possible examination of kidney function in health and disease. However, the majority of creatinine measurements are ordered as part of a basic metabolic panel and often meant as a screening test for possible kidney dysfunction. This is routine practice among many physicians, all over the western world. This basic metabolic panel serves for assessment and monitoring of hundreds of conditions, many unrelated to renal function. Consequently, most Scr concentrations may be considered as within the so-called normal range (results from apparently healthy individuals). Often, practical medicine is basically founded on comparison of normal with abnormal values. If medicine is to be scientific, we must not only understand the structural, functional and chemical relations operating in individuals, but we must also understand the basis of our comparisons. Today, almost 50 years later, in the age of evidence-based medicine, and in contrast with the enormous developments in the field of medicine, a sound basis for these comparsions is often lacking in the clinical laboratory. Nevertheless, the reference interval is the most widely used medical decision-making tool, even if its practical usefulness is lower than its theoretical power. This is due to the fact that obtaining a “good” reference interval is a very demanding activity, in terms of time, money and knowledge.

Based on chronologically obtained serum creatinine measurements, from the AZ Groeninge Hospital in Kortrijk, during the period from mid 2003 till end 2007, a database with about 350000 measurements, we calculated age/sex adjusted reference intervals for serum creatinine, measured by an enzymatic assay, traceable to the gold standard IDMS reference method. With the knowledge of reference intervals, there is no need to use the MDRD equation in the diagnosis of CKD.

 

Contact: Prof. Dr. Hans Pottel