Transcription

F R E Q U E N T LY A S K E D Q U E S T I O N S A B O U TGFR Estimates

ASSESSMENT OF KIDNEY FUNCTION.41]What is GFR?.42]Why assess GFR as an index of kidney function?.43]How does age affect GFR in adults?.44] How is GFR assessed?.45]What is a filtration marker?.46] Why is GFR indexed for body surface area?.57]How is the accuracy of the GFR assessments described?.531] What is cystatin C and how is serum cystatin Cused in cystatin C-based GFR estimating equations(eGFRcys)? . 1232] Is cystatin C a more accurate filtration marker thancreatinine?. 1333] Can serum cystatin C (Scys) be used alone for GFRestimation?. 1334] What is the currently recommended equation toestimate GFR from serum cystatin C?. 1335] Why is eGFRcr-cys more accurate than eithereGFRcr or eGFRcys?. 139] How is GFR estimated?.536] Cystatin C and risk. 1410] What problems are caused by the non-steady stateof endogenous filtration markers after a change in GFR?.637] When should cystatin C be measured?. 1411] What is the recommended approach for evaluationof GFR?.6INTERPRETATION OF GFR ESTIMATES. 1538] How should differences in a patient’s eGFR beinterpreted during the transition from the old to thenew equations?. 1513] Can serum creatinine be used alone for GFR estimation?. 739] To which populations or individuals do the CKD-EPI2021 equations not apply?. 1514] What is the difference between creatinineclearance and GFR?. 740] Why is the Cockcroft-Gault equation still used,even though it is less accurate?. 1515] What is the currently recommended equation toestimate GFR from serum creatinine?. 741] How should GFR estimates be used to detect CKD? . 1516] What is the Cockcroft-Gault formula? .817] What is the MDRD Study equation?.842] How can GFR estimates be used to detect progression?.1643] Do some drugs affect the accuracy of GFR estimates?. 1644] Should indexed or non-indexed eGFR be usedwhen dosing medications?. 1619] Why was the CKD-EPI creatinine equation revisedin 2021?.945] Can the estimating equations for GFR be used inacute kidney injury?. 1620] What is the difference in eGFRcr using the 2021versus the 2009 equation? .1046] Can GFR estimates be used in hospitalized patients?. 1621] Should clinical laboratories report eGFR when Scris measured?.10CHRONIC KIDNEY DISEASE.1747] What is the public health problem associated with CKD?.1748] What is the definition of CKD and how is GFR usedas a criterion for CKD?.1723] Why might different laboratories or health systemsreport different eGFR for the same patient?.1049] What are the stages of CKD?. 1824] Are calculators available for the CKD-EPI creatinine,MDRD Study, or Cockcroft-Gault equations?. 1151] What is the recommended method to screen foralbuminuria or proteinuria?. 1825] What factors affect creatinine generation? . 1152] What are the complications and commoncomorbidities associated with CKD?. 1926] What factors affect creatinine secretion? . 1127] What is the impact of calibration and interlaboratory variation of serum creatinine assays onthe estimation of GFR?. 11CHRONICKIDNEY DISEASE18] What is the 2009 CKD-EPI creatinine equation?.822] Should clinical laboratories that use the MDRDStudy equation for GFR reporting also change tothe 2021 CKD-EPI creatinine equation?.10INTERPRETATIONOF GFR ESTIMATES8] How is GFR measured?.512] What is creatinine and how is serum creatinineused in creatinine-based GFR estimating equations(eGFRcr)?.6ASSESSMENT OFKIDNEY FUNCTIONTABLE OF CONTENTS50] What are markers of kidney damage?. 1853] Does the risk of complications increase as kidneydisease progresses?. 1954] When should patients with kidney disease bereferred to a nephrologist?. 1929] What was the effect of standardization of thecreatinine assay on GFR estimates?. 12BIBLIOGRAPHY. 2030] What are indications for confirmation of eGFRcr?. 12FREQUENTLY ASKED QUESTIONS ABOUT GFR ESTIMATES3BIBLIOGRAPHY28] What factors affect the creatinine assays?. 12

ASSESSMENT OFKIDNEY FUNCTIONASSESSMENT OF KIDNEY FUNCTION1] What is GFR?3] How does age affect GFR in adults?GFR (glomerular filtration rate) is equal to the total of thefiltration rates of the functioning nephrons in the kidney.GFR is considered the most useful index of kidney functionin health and disease, which in conjunction with albuminuria, generally assessed from urine albumin-to-creatinineratio (uACR), can help determine the presence and severityof chronic kidney disease (CKD).GFR generally declines with age. However, there appearsto be substantial variation among individuals, and reasonsfor decline are not completely known (healthy aging,disease, or other factors). The threshold to diagnose CKDdoes not differ by age. At all ages, GFR is an independentpredictor of adverse outcomes, such as death, cardiovascular disease, and other CKD complications. In addition,decreased GFR in the elderly may require adjustment indrug dosages, as with younger patients with decreasedGFR. Some have proposed age-stratified GFR criteria forthe diagnosis of CKD.2] Why assess GFR as an index of kidneyfunction?GFR is considered the best index of kidney function inhealth and disease. The level of GFR and its magnitude ofchange over time are important to: Detect CKD Understand the severity or stage of CKD Make decisions about diagnosis, prognosis, andtreatment of CKD.Normal GFR varies according to age, sex, and body size; inyoung adults, it is approximately 120 mL/min/1.73 m2 anddeclines with age. A decrease in GFR precedes the onsetof kidney failure. Therefore, a persistently reduced GFR is aspecific diagnostic criterion for CKD. Below 60 mL/min/1.73m2, the prevalence of complications of CKD increases, asdoes the risk of cardiovascular disease (CVD).Table 1 lists clinical conditions where assessment of GFR isimportant.4] How is GFR assessed?GFR cannot be measured directly. It can be assessed asmeasured (mGFR) or estimated (eGFR) from the clearanceor serum (plasma) concentration of a filtration marker,respectively.5] What is a filtration marker?Filtration markers are exogenous or endogenous soluteswith molecular weight less than approximately 20,000Daltons whose serum concentration varies inversely withGFR and can be used to measure or estimate GFR. Anideal filtration marker is freely filtered by the glomeruli(not protein-bound), is not reabsorbed or secreted by thetubules, does not affect kidney function, and is easy tomeasure. Exogenous filtration markers include inulin (thegold standard), iothalamate, iohexol, EDTA, DTPA, andsynthetic polymers. Endogenous filtration markers includeTABLE 1: CLINICAL CONDITIONS WHERE ASSESSMENT OF GFR IS IMPORTANT *CLINICAL DECISIONSDiagnosisPrognosisCURRENT LEVEL OF GFRCHANGE IN LEVEL OF GFR Detection of CKD Detection of AKI Evaluation for kidney donation Detection of CKD progression Risk of CKD complications Risk for kidney failure Risk for CVD Risk for mortalityTreatment Dosage and monitoring for medicationscleared by the kidney Determine safety of diagnostic tests orprocedures Treatment of AKI Monitoring drug toxicity Referral to nephrologists Referral for kidney transplantation Placement of dialysis accessAbbreviations: AKI: acute kidney injury; CKD: chronic kidney disease; CVD: cardiovascular disease.*Reprinted with permission from the American Society of Nephrology via the Copyright Clearance Center. Stevens LA, Levey AS.J Am Soc Nephrol. 2009;20:2305–2313.4NATIONAL KIDNEY FOUNDATION

Table 1. Clinical conditions where assessment of GFR is importantClinicalDecisions6] Why is GFR indexed for body surface area?TreatmentKidney function is proportional to kidney size, which isproportional to body surface area (BSA). Adjustment forBSA is necessary when comparing a person’s GFR tonormal values, to the GFR criterion for the diagnosis ofCKD, and to levels defining the stages of CKD. A BSA of1.73 m2 was the normal mean value for young adults whenindexing was proposed. BSA can be computed using theformula of DuBois and DuBois.BSA (m2) 0.007184 x W0.425 x H0.725(where height is measured in centimeters,and weight in kilograms)Indexed GFR is less than non-indexed GFR in people withlarge BSA (tall or obese) and greater than non-indexed GFRin people with small BSA (short or very thin). Indexed GFRmay be converted to non-indexed GFR by the formula:non-indexed GFR indexed GFR x BSA (m2)/1.73 m27] How is the accuracy of the GFRassessments described?Detection of CKDChange in Level of GDetection of AKIevidence of accuracy compared to the classic method:Evaluation for kidney donationDetection of CKD progreurinary clearance of iothalamate, plasma clearance ofRisk of CKD complicationsRisk for kidney failureiohexol, and urinary and plasma clearance of Cr-EDTA (notRisk for CVDavailable in US). In general, plasma clearance methodsRisk for mortalityhave greater precision than urinary clearance methods.Dose and monitoring for medicationsTreatment of AKISpecial circumstances in which mGFR may be necessary inclearedbythekidneyselected cases for clinical practice decision making includeof diagnostictests donorMonitoringtheDetermineassessmentsafetyof a potentialliving kidneyand infre- drug toxicityor forproceduresquentlymedication dosing for critical drugs.ASSESSMENT OFKIDNEY FUNCTIONDiagnosismetabolites (creatinine is most commonly used) and lowmolecular weight proteins (cystatin C, beta-2 microglobulin,Prognosisand beta-trace protein).Current Level of GFRReferral to nephrologistsReferralfor kidneytransplantation OF THEFIGURE1: DETERMINANTSPlacementof dialysisSERUMLEVELaccessOF ENDOGENOUSFILTRATION MARKERS *MILKG(diet)G(cells)PE(gut, liver)U V(kidney)U V GFR P – TR TSG – E GFR P – TR TSGFR (G TR – TS – E)/PFigure1. Determinantsof levelthe (P)serumlevel of endogenousThe plasmaof an endogenousfiltration marker is filtrationdetermined markers. The pErrors in diagnostic tests can arise from systematicerrorby its generation(G) fromcells andisdiet,extrarenal eterminedbyits(E)generation (G) from(bias, average difference from the reference or “gold” stanby gut and liver, and urinary excretion (UV) by the kidney. Urinarydiet,extrarenalexcretioneliminationby gutandx liver,andurinary excretion (UV) bdard) or random error (imprecision, variabilityandof thedifferis the sum(E)of filteredload (GFRP), dystate,urinaryexcretionkidney.excretion is the sum of filtered load (GFR P), tubular secretion (TSences about the average difference). AccuracyreflectsUrinaryaequals generation and extrarenal elimination. By substitution andreabsorptionthe steadyGFRstate,generation and extracombination of absence of bias (“trueness”) andprecision; (TR). Inrearrangement,can beurinaryexpressedexcretionas the ratio ofequalsthe eexpressedas the ratio othere are many metrics for describing accuracy. Common*Reprinted with permission from the American Society of Nephrologynon-GFRTS, TR,andCenter.E) toStevensthe plasmametrics for describing accuracy of GFR assessmentsaredeterminantsvia the(G,CopyrightClearanceLA, Levey level.AS. J Am SocNephrol. 2009;20:2305–2313.bias (mean or median difference) on the GFR scale (a lowervalue is more accurate), and the proportion of assessmentsthose patients in whom a measured GFR of the surrogates to some of these pthat are within a specified percentage of the referenceshouldbe isconsidered.iologic processes, leading to erro9] How is GFR estimated?standard (for example, within 15% or 30%, a highervaluesomefromindividuals.more accurate, see below).Estimated GFR (eGFR) is determinedestimatingCreatinine-basedestimating eequations that incorporate the steady-stateserumconcentration of onefiltrationNON-GFR DETERMINANTSOFor more endogenoustions includeage, gender, race, or w8] How is GFR enot anSERUMas surrogates forisdifferencesin creatMeasured GFR (mGFR) is determined from theurinary LEVELS OFadequatemarkerofGFRastheserumconcentrationsof allENDOGENOUSFILTRATIONgeneration from musclemass (Tor plasma clearance of an exogenous filtrationmarker.filtration markers are affected by physiologicalHowever, these procedures are cumbersomeMARKERSand not used2).2,7 People processeswho are at the ionin routine clinical practice but may be used as confirmamuscle mass and diet, who are malnfrom cells and diet, tubular secretion and reabsorption, andtory tests in special circumstances and in researchstudies. renalGeneration,excretion (filtration, ished or have a reduction in muscleextra-renal elimination (Figure 1). GFR estimating equationsUrinary clearance of inulin during a continuous infusion issecretion, and reabsorption),andandexfromillnessor amputation,who ainclude demographicclinicalvariablesas surrogatesofthe classic method of Homer Smith. This procedure hastrarenal esthanthese non-GFR determinants. Accuracy of GFR estimates islimited precision; only approximately 90% of repeatedlevels of endogenouscludedin studieslimitedfiltrationby non-GFRmarkersdeterminantsof filtrationmarkers;usedonly for developmeasurements are within 15% of the initial ns,orwho have chang(P15 90%). This mGFR procedure is rarely used, even80–90%)(Figure 2).aseasily measured(P30 clinicalvariablesthe non-GFR determinants over timin research studies. The following alternative clearancemethods and filtration markers had strong to surrogatesmoderatefor these unmeasured physiologic processes and provide more acFREQUENTLYASKEDestimatesQUESTIONS thanABOUTtheGFRserumESTIMATEScuratelevelalone.6 However, by design, equationscapture only the average relationshipmost likely to have large differencetween mGFR and eGFR.6,8 –105 with the iOne of the challengesduction of a novel filtration markerclinical practice is that the non-GF

ASSESSMENT OFKIDNEY FUNCTIONFIGURE 3: EFFECT OF AN ACUTE GFRDECLINE ON GENERATION, FILTRATION,www.jasn.org BALANCE, AND SERUM LEVELBRIEF REVIEWEXCRETION,OF ENDOGENOUS FILTRATION MARKERS*GFR. In the non-steady state, the direction of change in theserum level indicates the direction of change in GFR, andthe rate of change in the serum level provides some indication of the magnitude of the change in GFR.to an idealfiltrationmarker relevant for11] Whatis therecommendedapproach forassessinglevelofGFRinrangesimporevaluation of GFR?Acute GFR Declinetant for clinical decision making. ImpreThe ovingrandom errorin Outcomes6060(KDIGO)CKD GuidelinesrecommendeGFR from Scrperformanceof the clearanceprocedureMarker generationor assaytheinitialfiltrationMea(eGFRcr)to beofthetest marker.in the assessmentin adultsunderDay Pmarker eGFRsincesurementseGFRcr is performedthe simplest,leaststandardexpensive, most widely01.0120conditions will minimize biologic variaavailable method worldwide, allowing GFR estimation withMarker filtration1.6791.5tion and will reduce the likelihood ofand ost clinicalsettings. Ifrandombiaserrors.is inaccurate,confirmarepeated measurement over a short time.2.0603.0ImprecisionmGFR isCrelevantfor as-GFR, measuredtory testingusingincystatinto estimatesessmentof changein GFRover time.InmGFR should becreatinineclearance(seeQuestion8), orCumulative formed (Figure 3).sion both affect the measured level andmust be considered in the interpretation2.02.0FIGURE 3: ASSESSMENT OF GFRof mGFR. To evaluate the extent of the1.51.5available literature and to provide dataPlasma marker1.01.0concentrationfor this discussion, we performed a sysInitial test - eGFRcrtemic review of all studies that compared01234simultaneous measurements of iohexol,Dayiothalamate, and inulin or repeated meaEffect of an acute GFR decline on generation, filtration, excretion,Figure 2. Effectof an acute GFR decline on generation, filtration, excretion, balance, surements of these markers using thebalance, and serum level of endogenous filtration markers. Afterand serum level of endogenous filtration markers. After an acute GFR decline, generation same protocol (Table 5).16 – 43 The grayan acute GFR decline, generation of the marker is unchanged, butof the markerfiltrationis unchanged,but filtrationand excretionreduced,resulting in retention shaded boxes in Table 5 show the studiesand excretionare reduced,resulting inareretentionof theof the marker(a risingpositiverisingplasmaplasmalevel(non–steady state). that report repeated measurements usmarker(a risingpositivebalance)balance) andand aarisinglevel(non–Consider sources of error and needDuring this time,lowerthisthanGFR.GFRGFR.remainsreduced, the rise insteadyeGFRstate). isDuringtime,eGFRAlthoughis lower thanAlthoughing the sameprotocol.Otherassessmentmarkersfor moreaccurateplasma levelGFRleadsto anreduced,increasethein risefilteredload level(the leadsproductGFR times the plasmaremainsin plasmato anofincreaseandtheircomparisontoinulinare alsoin filteredequalsload (theproduct ofAtGFRtimesthecumulativeplasma level)balanceuntillevel) until filtrationgeneration.thattime,and the thattime,cumulativebalanceandthelevel plateau at a new steady state. In the new steady state, eGFR approximates mGFR.12090120GFR902plasma inlevelplateauat a new persteadystate. Inthe1.73new msteadystate, secretion andGFR is expressedunitsof milliliterminuteper. TubulareGFR approximates mGFR. GFR is expressed in units of milliliter perreabsorption and extrarenal2 elimination are assumed to be zero. Modified and reprominute per 1.73 m . Tubular secretion and reabsorption and extrarenalduced with permission from Kassirer JP, N Engl J Med 285: 385–389, 1971.elimination are assumed to be zero. *Modified and reproduced withpermission from Kassirer JP.NoCLEARANCE METHODSYesTable 3. Indications for measuredN Engl J Med. 1971;285:385–389.GFRPerform confirmatory testsoral water loading to stimulate diuresis, Urinary Clearanceand assesstheir consistencybladder catheterization to assure com- Urinary clearanceis the mostdirectExtremes of age and body sizeplete urine collection, and careful timing method for measurement of GFR. ClearSevere malnutrition or obesityof blood sampling at the midpoint of the ance is computed as the urine concentraDisease of skeletal muscle14 However, inulin is difurine collection.tion of the exogenous or endogenous fil10]Whatproblemsarecausedby thenonParaplegia or ion marker, multiplied by the volumesteadystate of endogenous filtrationEvaluation for ,of the timed urine sample, and dividedVegetarian dietmarkers after a change in GFR?we use alterative clearance methods and by the average plasma concentrationBefore administration of prolonged .the serumlevelTableof an4 summarizes during the same timeof toxicAccuratemedicationsestimation of GFR fromthe strengthslimitationsMeasurement of the clearance of anendogenous filtration marker (creatinineorandcystatinC) of the goldstandard method, as well as other the endogenous filtration marker, such asrequires a steady state; that is, the serum level is stableulus, neither reabsorbed, secreted, syn- clearance methods and markers.creatinine, is performed in virtually evday to day.is true whetherserumlevelmarkersalone deviate ery clinical center. A long urinary collecthesized, fromor metabolizedbyThisthe tubules,All theotherfiltrationusedto estimateGFRoforthethe serumlevelis usedandin an12] Whatis creatinineis serumand doesisnotalterthe functionfrom idealbehavior,clearance meation period—6 to 24 h—isandused howto avoidkidney. estimationInulin, a 5200-D,inert,unthe requirementfor waterloading, andsurementsare difficultto perform; thus, creatinineequation.Aftera declinein GFR,the serumusedin creatinine-basedGFRcharged polymerof untilfructose,is theonly statevaluesfor mGFR (Figureusually containan ele- estimatingin the steady state,a single bloodsamplelevel risesa newsteadyis achieved2).equations(eGFRcr)?known idealfiltrationmarker.Theis clasof estimateerror, whichdifferentiates it obtained either at the beginning or endWhenthe serumlevelrising, mentthe GFRbasedCreatininea 113 Daperiodaminomayacidsic clearance method of Homer Smith in- from true physiologic GFR. Bias generof the iscollectionbederivativeassumed that is generon thenon-steadyserumallyleveloverestimatesthe breakdowncreatinein muscle, distributedcludes fastingconditionsin thestatemorning,reflectssystematic thedifferences in atedre- fromto representthe y,rise in GFR,the seruma continuousintravenousmul- r tration totalduringtheurinecollection.body water, and excreted by the kidneyslevel declinesuntil a newsteadystateis achieved.When This biasbytiple clearanceperiods requiringrepetiassayof thefiltration marker.is glomerularTimed collectionsto ough thetive bloodtheandserumurine collectionsover 3 h, theassessedexperimentallyby thecomparison caused by inaccurate record of time andlevel is declining,GFR estimatebased onserum concentration of creatinine is affected primarily bynon-steady state serum level underestimates the measuredthe level of GFR, it is also affected by other physiological2308Journal of the American Society of Nephrology6J Am Soc Nephrol 20: 2305–2313, 2009NATIONAL KIDNEY FOUNDATION

ASSESSMENT OFKIDNEY FUNCTIONTABLE 2: THE SAME SERUM CREATININE: DIFFERENT eGFR58-YR-OLD MAN80-YR-OLD WOMANSerum creatinine1.20 mg/dLGFR as estimated by t he2021 CKD-EPI equation70 mL/min/1.73 mKidney functionMild reduction in GFRModerate reduction in GFRStage G2 CKD if kidney damage is alsopresent such as albuminuriaStage G3a CKD whether or not kidneydamage is presentprocesses (non-GFR determinants): generation frommuscle or diet, tubular secretion by active transport, andextrarenal elimination by gastrointestinal bacteria or loss of“third-space” extracellular fluid. GFR estimating equationsconvert the serum creatinine concentration to the GFRscale and adjust for variation in non-GFR determinants thatvary by age and sex, which provides a more meaningfulassessment of GFR.13] Can serum creatinine be used alone forGFR estimation?No. Due to variation in these processes among individualsand over time within individuals, particularly the variation in creatinine generation, the cutoff for normal versusabnormal serum creatinine concentration differs amonggroups (Table 2); however, clinical laboratories generallyreport a single reference range for all adults. Because ofthe wide range of normal for serum creatinine in most clinical laboratories, GFR must decline to approximately halfthe normal level before the serum creatinine concentrationrises above the upper limit of normal. Thus, an increase inserum creatinine almost always reflects a reduction in GFR,but people with decreased GFR may have normal serumcreatinine.14] What is the difference between creatinineclearance and GFR?Creatinine is secreted by the proximal tubule as well asfiltered by the glomeruli, thus creatinine clearance (Clcr)exceeds GFR by about 10% to 40% at all levels of GFR (thedifference is higher at higher GFR and lower at lower GFR).1.20 mg/dL49 mL/min/1.73 m22Clcr can be measured (mClcr) from serum creatinine andcreatinine excretion in a timed urine collection or estimatedfrom serum creatinine using estimating equations (eClcr),such as the Cockcroft-Gault or Jelliffe equations. As withother clearance measurements, mClcr is inconvenient andfrequently inaccurate. mClcr does not meet the criterionfor acceptable accuracy compared to mGFR.15] What is the currently recommendedequation to estimate GFR from serumcreatinine?The National Institute of Diabetes and Digestive and KidneyDiseases (NIDDK), National Kidney Foundation (NKF),and American Society of Nephrology (ASN) recommendestimating GFR from serum creatinine using the 2021CKD-EPI creatinine equations in people 18 years and older.This recommendation builds on prior recommendationsas discussed below. In Table 3 contains a summary of thepreviously recommended equations. See Questions 16 to19 for details. For children, the recommended equations forestimating GFR are the 2009 Schwartz bedside creatinineequation or the 2012 CKiD creatinine-cystatin equation(Pediatric GFR Calculator National Kidney Foundation).16] What is the Cockcroft-Gault formula?The Cockcroft-Gault formula was developed in 1976 usingdata from 249 men to estimate mClcr from approximately30 to130 mL/min. It is not adjusted for body surface areaand is not expressed for use with standardized Scr. In1998, the US FDA recommended use of eClcr using theTABLE 3: EQUATIONS TO ESTIMATE GFREQUATION (YEAR)POPULATIONREFERENCE METHODSUNITSFACTORSRECOMMENDATIONS(YEAR)CKD-EPI (2021)CKD-EPI (2012)MDRD Study(1999/2005)Cockcroft-Gault (1978)DiverseDiverseCKDWhite menmGFRmGFRmL/min/1.73 m2mL/min/1.73 mmGFR2mL/min/1.73 mmClcr2mL/minScr, age, sexScr, age, sex, raceScr, age, sex, raceScr, age, sex, weightNKF-ASN Task ForceFinal Report (2021)KDIGO (2013), KDOQI(2014), FDA (2020)KDOQI (2002), FDA(2020)FDA (1998), KDOQI(2002)FREQUENTLY ASKED QUESTIONS ABOUT GFR ESTIMATES7

ASSESSMENT OFKIDNEY FUNCTIONCockcroft-Gault formula in drug development programsand for dose-adjustment of approved drugs in patientswith decreased kidney function.eClcr {((140-age) x weight)/(72 SCr)} x 0.85 if femalewhere eClcr is expressed in milliliters per minute, age inyears, weight in kilograms, and serum creatinine (SCr) inmilligrams per deciliter. It was recommended by the 2002Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines for routine GFR evaluation but is no longer recommended for this purpose (see Question 40.17] What is the MDRD Study equation?The 4-variable MDRD Study equation was developed in1999 using data from 1628 patients with CKD, aged 18 to70, predominantly Caucasian, nondiabetic, and with GFRfrom approximately 5 to 90 mL/min/1.73 m2. It estimatesmGFR adjusted for body surface area and is more accuratethan mClcr using 24-hour urine collections or eClcr usingthe Cockcroft-Gault formula.4 It underestimates mGFR athigher values of eGFR, so values above 60 mL/min/1.73 m2may not be reported as a numeric value. The equation is:The CKD-EPI equation estimates GFR from serum creatinine, age, sex, and race.eGFR 141 x min SCr/k, 1) α x max(SCr /k, 1)-1.209 x 0.993Agex 1.018 [if female]x 1.159 [if Black].eGFR is expressed in mL/min/1.73 m2 SCr is serum creatinine expressed in mg/dL, and age is expressed in years.Article Development and Comparison of a New Equation to Estimate GFRArticleDevelopmentand Comparisona New Equation to Estimate GFRFIGURE 4:COMPARISONOFofPERFORMANCEOF MODIFICATION OF DIET IN RENALDISEASE (MDRD) STUDY AND CHRONICequations in estimating measured GFR in the externalFigure. Per

Evaluation for kidney donation Detection of AKI Detection of CKD progression Prognosis Risk of CKD complications Risk for CVD Risk for mortality Risk for kidney failure Treatment Dosage and monitoring for medications cleared by the kidney Determine safety of diagnostic tests or procedures Referral to .