Kidney function can be evaluated by determining the glomerular filtration rate (GFR), which provides an estimate of how well the kidneys are removing waste and excess fluid from the blood. The GFR is not measured directly. Instead, a measurement of serum creatinine is performed, and this value is entered into an equation that estimates GFR. Hence, accurate determination of serum creatinine is essential for meaningful estimation of GFR and assessment of kidney function. The National Kidney Disease Education Program (NKDEP) has initiated a creatinine standardization program that is intended to help in-vitro diagnostic (IVD) manufacturers and clinical laboratories address inter-laboratory variations in creatinine measurements. NKDEP has encouraged IVD manufacturers to purchase SRM 967 as part of this standardization program. As a result, SRM 967 was widely adopted by the clinical diagnostics community. SRM 967 was introduced in early 2007, and was superseded by SRM 967a in 2009.