Diagnostic serum creatinine studies are used to determine renal function. The reference interval is 0.6–1.3 mg/dL (53–115 μmol/L). Measuring serum creatinine is a simple test, and it is the most commonly used indicator of renal function.
A rise in blood creatinine concentration is a late marker, observed only with marked damage to functioning nephrons. Therefore, this test is unsuitable for detecting early-stage kidney disease. A better estimation of kidney function is given by calculating the estimated glomerular filtration rate (eGFR). eGFR can be accurately calculated without a 24-hour urine collection using serum creatinine concentration and some or all of the following variables: sex, age, weight, and (no longer https://www.kidney.org/content/laboratory-implementation-nkf-asn-task-force-reassessing-inclusion-race-diagnosing-kidney) race, as suggested by the American Diabetes Association. Many laboratories will automatically calculate eGFR when a creatinine test is requested. Algorithms to estimate GFR from creatinine concentration and other parameters are discussed in the renal function article.
A concern as of late 2010 relates to the adoption of a new analytical methodology, and a possible impact this may have in clinical medicine.  Most clinical laboratories now align their creatinine measurements against a new standardized isotope dilution mass spectrometry (IDMS) method to measure serum creatinine. IDMS appears to give lower values than older methods when the serum creatinine values are relatively low, for example 0.7 mg/dL. The IDMS method would result in a comparative overestimation of the corresponding calculated GFR in some patients with normal renal function. A few medicines are dosed even in normal renal function on that derived GFR. The dose, unless further modified, could now be higher than desired, potentially causing increased drug-related toxicity. To counter the effect of changing to IDMS, new FDA guidelines have suggested limiting doses to specified maxima with carboplatin, a chemotherapy drug.
A 2009 Japanese study found a lower serum creatinine concentration to be associated with an increased risk for the development of type 2 diabetes in Japanese men.