KDOQI GUIDELINE 4 ESTIMATION OF GFRWord文档格式.docx
- 文档编号:7564091
- 上传时间:2023-05-08
- 格式:DOCX
- 页数:24
- 大小:589.40KB
KDOQI GUIDELINE 4 ESTIMATION OF GFRWord文档格式.docx
《KDOQI GUIDELINE 4 ESTIMATION OF GFRWord文档格式.docx》由会员分享,可在线阅读,更多相关《KDOQI GUIDELINE 4 ESTIMATION OF GFRWord文档格式.docx(24页珍藏版)》请在冰点文库上搜索。
GUIDELINE4.ESTIMATIONOFGFR
EstimatesofGFRarethebestoverallindicesofthelevelofkidneyfunction.
ThelevelofGFRshouldbeestimatedfrompredictionequationsthattakeintoaccounttheserumcreatinineconcentrationandsomeorallofthefollowingvariables:
age,gender,race,andbodysize.ThefollowingequationsprovideusefulestimatesofGFR:
∙Inadults,theMDRDStudyandCockcroft-Gaultequations
∙Inchildren,theSchwartzandCounahan-Barrattequations.
∙Theserumcreatinineconcentrationaloneshouldnotbeusedtoassessthelevelofkidneyfunction.
∙ClinicallaboratoriesshouldreportanestimateofGFRusingapredictionequation,inadditiontoreportingtheserumcreatininemeasurement.
∙Autoanalyzermanufacturersandclinicallaboratoriesshouldcalibrateserumcreatinineassaysusinganinternationalstandard.
Measurementofcreatinineclearanceusingtimed(forexample,24-hour)urinecollectionsdoesnotimprovetheestimateofGFRoverthatprovidedbypredictionequations.A24-hoururinesampleprovidesusefulinformationfor:
∙EstimationofGFRinindividualswithexceptionaldietaryintake(vegetariandiet,creatinesupplements)ormusclemass(amputation,malnutrition,musclewasting);
∙Assessmentofdietandnutritionalstatus;
∙Needtostartdialysis.
Background
Glomerularfiltrationrate(GFR)providesanexcellentmeasureofthefilteringcapacityofthekidneys.AlowordecreasingGFRisagoodindexofchronickidneydisease.SincethetotalkidneyGFRisequaltothesumofthefiltrationratesineachofthefunctioningnephrons,thetotalGFRcanbeusedasanindexoffunctioningrenalmass.111AdecreaseinGFRprecedeskidneyfailureinallformsofprogressivekidneydisease.MonitoringchangesinGFRcandelineateprogressionofkidneydisease.ThelevelofGFRisastrongpredictorofthetimetoonsetofkidneyfailureaswellastheriskofcomplicationsofchronickidneydisease.Additionally,estimationofGFRinclinicalpracticeallowsproperdosingofdrugsexcretedbyglomerularfiltrationtoavoidpotentialdrugtoxicity.
Glomerularfiltrationratecannotbemeasureddirectly.Ifasubstanceinstableconcentrationintheplasmaisphysiologicallyinert,freelyfilteredattheglomerulus,andneithersecreted,reabsorbed,synthesized,normetabolizedbythekidney,theamountofthatsubstancefilteredattheglomerulusisequaltotheamountexcretedintheurine.ThefructosepolysaccharideinulinhaseachoftheabovepropertiesandhaslongbeenconsideredanidealsubstancetoestimateGFR.TheamountofinulinfilteredattheglomerulusequalstheGFRmultipliedbytheplasmainulinconcentration:
GFR�Pin.Theamountofexcretedinulinequalstheurineinulinconcentration(Uin)multipliedbytheurineflowrate(V,volumeexcretedperunittime).
Sincefilteredinulin=excretedinulin:
(1)GFR譖in=Uin譜
(2)
Theterm(Uin�V)/PinisdefinedastheclearanceofinulinandisanaccurateestimateofGFR.Theinulinclearance,inmL/min,referstothatvolumeofplasmaperunittimethatisclearedofinulinbyrenalexcretion.
Rationale
CriterionStandard
Inulinclearanceiswidelyregardedasthegoldstandardformeasuringglomerularfiltrationrate.Inulinclearancemeasurementsinhealthy,hydratedyoungadults(adjustedtoastandardbodysurfaceareaof1.73m2)havemeanvaluesof127mL/min/1.73m2inmenand118mL/min/1.73m2inwomenwithastandarddeviationofapproximately20mL/min/1.73m2.67Amongadults,numerousstudiessuggestthatglomerularfiltrationrateisloweratolderages.Afterage20to30years,GFRdecreasesbyapproximately1.0mL/min/1.73m2peryearwithsubstantialinter-individualvariationevenamong“healthy”individuals.112,113Whetherthisaveragedeclinewithagingisoptimalintermsofpredictingtheriskofcomplicationsofdecreasedkidneyfunctionandmortalityisunknown.
Glomerularfiltrationrateintheinfantdiffersquantitativelyfromthatinolderchildrenandadults.Duringinfancyandthroughthefirst12to18monthsoflife,GFRincreaseswithmaturation69-71(seeTable23,Guideline1).InulinclearanceisalsothegoldstandardtomeasureGFRinchildren,butisparticularlydifficultintheneonatebecauseofthelowerGFRofneonatesandtheirrelativelylargerextracellularfluidcompartment.Thesefactorsextendthestudytimenecessaryfortechniquesrelyingonequilibrationofthemarkersubstanceandmonitoringofitsplasmadisappearancerate.Additionally,accurateassessmentoftheurineflowraterequiresbladdercatheterizationininfantsandyoungchildren.
RationaleforAlternativeMeasures
Theclassicmethodofinulinclearancerequiresanintravenousinfusionandtimedurinecollectionsoveraperiodofseveralhoursmakingitcostlyandcumbersome.AsaresultanumberofalternativemeasuresforestimatingGFRhavebeendevised.Theurinaryclearanceofexogenousradioactivemarkers(125I-iothalamateand99mTc-DTPA)provideexcellentmeasuresofGFR114butarenotreadilyavailable.Plasmaclearanceofexogenoussubstancesincludingiohexoland51Cr-EDTAhasbeenusedaswellbutrequireestimatesofbodysize,whichdecreasestheirprecision.Capillaryelectrophoresisallowsformeasurementofnon-radiolabelediothalamateinbloodandurinewithpromisingresults.115SerumcystatinChasbeenusedtoestimateGFRbutdataareconflictingastowhetheritprovidesasufficientimprovementtowarrantwidespreadclinicaluse.116ThemostwidelyusedmeasuresofGFRinclinicalpracticearebasedonthe24-hourcreatinineclearanceorserumcreatinineconcentration.Asdiscussedbelow,eachofthesemeasurementsisassociatedwithseriouslimitations.
EquationstopredictGFRandcreatinineclearancefromserumcreatininehavebeentestedinalargenumberofstudieswhoseresultsarereviewed.UseofrelevantequationsinchildrenandadultshasbeenshowntogivemorevalidestimatesofGFRthanserumcreatininealone.Additionally,forthehealthcareprovider,itmaybeeasiertorecognizeclinicallyimportantchangesinkidneyfunctionwhendealingwithlargenumbersestimatingaphysiologicallyrelevantparameter(GFR)ratherthansmallnumbers(serumcreatinine)whichareinverselyrelatedtotherelevantparameter.
AccuracyofanEquationinEstimatingGFRCombinesItsBiasandPrecision
InchoosingapredictionequationtoestimateGFR,oneshouldconsiderboththebiasandprecisionoftheequation-generatedestimates.BiasexpressesthesystematicdeviationfromthegoldstandardmeasureofGFR.ApredictionequationthatconsistentlyoverestimatesorunderestimatesthegoldstandardmeasureofGFRyieldsabiasedestimate.
Anequallyimportantmeasureoftheusefulnessofapredictionequationisameasureofitsprecision.Precisionexpressesthevariability(ordispersion)ofpredictionequationestimatesaroundthegoldstandardGFRmeasure.
Accuracycombinesprecisionandbias.AusefulmeasureofaccuracyisadescriptionofpercentilesofthedistributionofthedifferencesbetweenestimatedandmeasuredGFR.Inotherwords,if99%ofthetimeapredictionequationyieldsanestimatewithin10%ofthemeasuredGFR,itwouldbeaveryaccurateandusefulclinicaltool.Achievingahighlevelofaccuracyrequiresbothlowbiasandhighprecision.Descriptionofthepercentofestimatesfallingwithin30%and50%aboveorbelowthemeasuredGFRisausefulmeasureofaccuracy.
ImportanceofSampleSize
Manyofthestudiesreviewedweresmall.Sinceestimatesofaccuracyfromsmallerstudiescanbeunreliable,studiespresentedhaveatleast100adultsor50children.SeverallargevalidationstudiesevaluatingthenewlydevelopedMDRDStudyequationwereconductedrecentlyandwereonlyavailableinabstractform.Inordertocapturethesevaluabledatatheauthorswerecontactedandaskedtoanalyzetheirdataandprovideestimatesofaccuracyforthisreview.AdditionaldetailsregardingtheevaluationofpredictionequationstoestimateGFRarereviewedinPart10,Appendix3.
StrengthofEvidence
SerumcreatininealoneisnotanaccurateindexofthelevelofGFR(R).TheuseoftheserumlevelofcreatinineasanindexofGFRrestsonthreeimportantassumptions:
(1)creatinineisanidealfiltrationmarkerwhoseclearanceapproximatesGFR;
(2)creatinineexcretionrateisconstantamongindividualsandovertime;
and(3)measurementofserumcreatinineisaccurateandreproducibleacrossclinicallaboratories.AlthoughtheserumcreatinineconcentrationcanprovidearoughindexofthelevelofGFR,noneoftheseassumptionsisstrictlytrue,andnumerousfactorscanleadtoerrorsinestimationofthelevelofGFRfromtheserumcreatinineconcentrationalone.
Creatinineexcretionbythekidney.Creatinineisfreelyfilteredbytheglomerulus,butisalsosecretedbytheproximaltubule.Hence,theamountofcreatinineexcretedintheurineisthecompositeofboththefilteredandsecretedcreatinineandcanberepresentedbythefollowingequation:
(3)UCr譜=GFR譖Cr+TSCr
whereTSCristherateoftubularcreatininesecretion.DividingbyPCr:
(4)CCr=GFR+CTSCr
whereCTSCristheclearanceofcreatinineduetotubularsecretion.Thus,creatinineclearancesystematicallyoverestimatesGFR.Thisoverestimationisapproximately10%to40%innormalindividuals,butisgreaterandmoreunpredictableinpatientswithchronickidneydisease(Fig12).
Figure12
RelationshipofcreatinineclearanceandserumcreatininewithGFR(inulinclearance)inpatientswit
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- KDOQI GUIDELINE ESTIMATION OF GFR