PharmPK Discussion - Calculating GFR

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• On 20 Jul 2006 at 11:44:31, "Bonate, Peter" (Peter.Bonate.-a-.genzyme.com) sent the message
`I am really confused on something and I hope someone can explain itto me.  We estimated inulin clearance for a group of patients.  Theunits are in mL/min.  Normal ranges are reported in mL/min/1.73 m**2.How do I convert mL/min to mL/min/1.73 m**2?  Do I divide inulin CLby (BSA/1.73)?Thanks,Pete BonatePeter L. Bonate, PhDGenzyme CorporationSenior Director, Pharmacokinetics4545 Horizon Hill BlvdSan Antonio, TX  78229   USApeter.bonate.aaa.genzyme.comphone: 210-949-8662fax: 210-949-8219`
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• On 21 Jul 2006 at 20:53:05, Larry Bauer (labauer.-a-.u.washington.edu) sent the message
`The following message was posted to: PharmPKHi Peter-  In a word, yes.  Another way to think about it is:  takethe patient's clearance in ml/min and divide it by their BSA--thiswill yield ml/min/m^2.  Then, multiply by 1.73 to get ml/min per1.73m^2--otherwise known as ml/min/1.73m^2  --Larry`
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• On 22 Jul 2006 at 10:03:48, wwolowic.aaa.nova.edu sent the message
`The following message was posted to: PharmPKThis reminds me of the debacle with the MDRD equation...and is moreconfusing than it looks.The inulin GFR is corrected or normalized to 1.73m**2, the BSA of thefictional average patient.to convert mL/min to mL/min/1.73m**2 for a specific patient, dividethat patients inulin GFR by their BSA which will give you mL/min/m**2(per m**2) , then multiply by 1.73 to normalize the value to an"average" individual of 1.73 m**2 BSA.ie[(ml/min) / (subjects BSA m**2)] * 1.73 = x mL/min/1.73 m**2Wolowich`
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• On 22 Jul 2006 at 07:29:11, "Dowling, Thomas" (tdowling.aaa.rx.umaryland.edu) sent the message
`Pete:The conversion is as follows:1. Calculate patient's BSA in m**22. Multiply Inulin CL (mL/min) x (1.73/BSA)Here, GFR values are standardized to a BSA of 1.73m**2. This approachis commonly used in clinical research but not widely accepted in theclinical setting (i.e. Cockcroft-Gault creatinine clearance isreported in mL/min). For example, patients with BSA >> 1.73m**2 (i.e.3.0 m**2) may have apparent GFR >> 200 mL/min, however when thisvalue is corrected to 1.73m**2, their result is usually in the normalrange of 90 - 140 mL/min/1.73m**2.Recently, the MDRD equation has been proposed for estimating GFR inthe clinical setting, and its units are mL/min/1.73m**2.Hope this helps,Tom`
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• On 23 Jul 2006 at 12:38:47, jmlanao.-at-.usal.es sent the message
`The standard formula for the calculation of the creatinine or inulinclearance corrected by BSA is the following:Clearance per standard surface area (mL/min/1.73 m2) = calculatedclearance * (1.73 / (BSA in square meters))An interesting paper about the normalization of GFR is:Peters AM, Gordon I, Sixt R. Normalization of glomerular filtration ratein children: body surface area, body weight or extracellular fluidvolume?J Nucl Med. 35(3):438-44.1994.Regards,Prof. Jose M. LanaoDpt. Pharmacy and Pharmaceutical TechnologyUniversity of SalamancaSpain`
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• On 24 Jul 2006 at 07:25:09, Nick Holford (n.holford.-at-.auckland.ac.nz) sent the message
`The following message was posted to: PharmPKHi,Just a note on the use of m**2 as as a standardising factor. The onlytheory I am aware of for the use of body surface area as a scalefactor for functional properties of the body such as GFR comes from adisproven allometric hypothesis.See http://www.cognigencorp.com/nonmem/nm/99oct042001.htmlThe current best allometric theories are based on a 3/4 powerfunction of weight."Commonly used in clinical research" does not mean it is a sensiblething to do. Althought the BSA scaling method is better than a simpleper kg standardisation clinical researchers should use the 3/4 powerallometric function for GFR if they want to be scientific.Nick--Nick Holford, Dept Pharmacology & Clinical PharmacologyUniversity of Auckland, 85 Park Rd, Private Bag 92019, Auckland, NewZealandemail:n.holford.aaa.auckland.ac.nz tel:+64(9)373-7599x86730 fax:373-7556http://www.health.auckland.ac.nz/pharmacology/staff/nholford/`
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