Editing Creatinine (section)

==Diagnostic use==
Serum creatinine is the most commonly used indicator (although not a direct measure) of [[renal function]]. A raised creatinine is not always representative of a true reduction in GFR. A high reading may be due to increased production of creatinine not due to reduced kidney function, to interference with the assay, or to reduced tubular secretion of creatinine. An increase in serum creatinine can be due to increased ingestion of cooked meat (which contains creatinine converted from creatine by the heat from cooking) or excessive intake of protein and creatine supplements, taken to enhance athletic performance. Intense exercise can increase creatinine by increasing muscle breakdown. 

[[Dehydration]] secondary to an inflammatory process with fever may cause a false increase in creatinine concentrations not related to actual kidney impairment, as in some cases associated with cholecystitis.{{Citation needed|date=December 2017}} Several medications and chromogens can interfere with the chemical assay. Creatinine secretion by the renal tubules can be blocked by some medications, again increasing measured creatinine.<ref name=pmid22745616>{{cite journal | vauthors = Samra M, Abcar AC | title = False estimates of elevated creatinine | journal = The Permanente Journal | volume = 16 | issue = 2 | pages = 51–2 | year = 2012 | pmid = 22745616 | pmc = 3383162 | doi = 10.7812/tpp/11-121 }}</ref>

=== Serum creatinine ===
Diagnostic serum creatinine studies are used to determine renal function.<ref name="Lewis_2016" /> The reference interval is 0.6–1.3&nbsp;mg/dL (53–115 μmol/L).<ref name="Lewis_2016" /> It is simple to measure serum creatinine, and it is the most commonly used indicator of renal function.<ref name=ClinChem89>{{cite book| vauthors = Taylor EH |title=Clinical Chemistry|year=1989|publisher=Wiley |isbn=0-471-85342-9 |oclc=19065010 |pages=4, 58–62}}</ref>

A rise in blood creatinine concentration is a late marker, observed only with marked damage to functioning [[nephron]]s. The test is therefore unsuitable for detecting early-stage [[kidney disease]]. A better estimate of kidney function is given by calculating the estimated glomerular filtration rate (eGFR). eGFR can be calculated without a 24-hour urine collection, using serum creatinine concentration and some or all of the following variables: sex, age, and weight, as suggested by the [[American Diabetes Association]].<ref>{{cite journal | vauthors = Gross JL, de Azevedo MJ, Silveiro SP, Canani LH, Caramori ML, Zelmanovitz T | title = Diabetic nephropathy: diagnosis, prevention, and treatment | journal = Diabetes Care | volume = 28 | issue = 1 | pages = 164–76 | date = January 2005 | pmid = 15616252 | doi = 10.2337/diacare.28.1.164 | doi-access = free }}</ref> 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#Estimated values|renal function]] article. Unfortunately, the MDRD Study equation was developed in people with chronic kidney disease, and its major limitations are imprecision and systematic underestimation of measured GFR (bias) at higher/normal values.<ref>{{cite journal | vauthors = Levey AS, Stevens LA, Schmid CH, Zhang YL, ((Castro AF 3rd)), Feldman HI, Kusek JW, Eggers P, Van Lente F, Greene T, Coresh J| title = A new equation to estimate glomerular filtration rate | journal = Ann Intern Med | date = 5 May 2009 | volume = 150 | issue = 9 | pages = 604–612 | pmid = 19414839 | pmc = 2763564 | doi = 10.7326/0003-4819-150-9-200905050-00006 | doi-access = free }}</ref>  

A concern as of late 2010 relates to the adoption of a new analytical method, and the possible effect 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&nbsp;mg/dL. The IDMS method would result in comparative overestimation of the corresponding calculated GFR in some patients with normal renal function. A few medicines are dosed even in normal renal function using that derived value of GFR. The dose, unless further modified, could then 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 of carboplatin, a chemotherapy drug, to specified maxima.<ref>{{cite web|url=https://www.fda.gov/AboutFDA/CentersOffices/CDER/ucm228974.htm|archive-url=https://web.archive.org/web/20111119090611/https://www.fda.gov/AboutFDA/CentersOffices/CDER/ucm228974.htm|archive-date=2011-11-19|title=Carboplatin dosing|website=[[Food and Drug Administration]]|department=Center for Drug Evaluation and Research|url-status=dead}}</ref>

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.<ref>{{cite journal | vauthors = Harita N, Hayashi T, Sato KK, Nakamura Y, Yoneda T, Endo G, Kambe H | title = Lower serum creatinine is a new risk factor of type 2 diabetes: the Kansai healthcare study | journal = Diabetes Care | volume = 32 | issue = 3 | pages = 424–6 | date = March 2009 | pmid = 19074997 | pmc = 2646021 | doi = 10.2337/dc08-1265 }}</ref>

===Urine creatinine===
Males produce approximately 150&nbsp;μmol to 200&nbsp;μmol of creatinine per kilogram of body weight per 24&nbsp;h, while females produce approximately 100&nbsp;μmol/kg/24&nbsp;h to 150&nbsp;μmol/kg/24&nbsp;h. In normal circumstances, all the creatinine produced is excreted in the urine.

Creatinine concentration is checked during standard urine drug tests. An expected creatinine concentration indicates that the test sample is undiluted, whereas low amounts of creatinine in the urine indicate either a manipulated test or low initial baseline creatinine concentrations. Test samples considered manipulated due to low creatinine are not tested, and the test is sometimes considered failed.