Red cell distribution width and risk of peripheral artery disease: Analysis of National Health and Nutrition Examination Survey

Transcription

1 442443VMJ / X Zlwdiy SK et l.vsculr Medicine 2012 Red cell distribution width nd risk of peripherl rtery disese: Anlysis of Ntionl Helth nd Nutrition Exmintion Survey Vsculr Medicine 17(3) The Author(s) 2012 Reprints nd permission: sgepub. co.uk/journlspermissions.nv DOI: / X vmj.sgepub.com Sndip K Zlwdiy, Viks Veernn, Sidkpl S Pnich nd Luis Afonso Abstrct Red cell distribution width (RDW) is n independent predictor of the 10-yer estimted risk of coronry hert disese (CHD) events. However, RDW s ssocition with peripherl rtery disese (PAD) CHD risk equivlent hs not been evluted to dte. In this cross-sectionl study, we exmined 6950 prticipnts of the Ntionl Helth nd Nutrition Exmintion Survey, PAD ws defined s n nkle brchil index below 0.9 (n = 618). RDW ws divided into qurtiles (Q) (Q1: 12.2; Q2: ; Q3: ; Q4: 13.1) nd PAD risk ws compred cross these qurtiles using djusted multivrite logistic regression. A grded increse in prevlent PAD with incresing RDW qurtiles ws observed (4.2% in Q1 vs 13.9% in Q4; test of trend p < 0.001). Risk of PAD ws significntly higher (odds rtio (OR) 1.19, 95% confidence intervl (CI): ; p = 0.003) fter djusting for ge, sex, rce, body mss index, hypertension, hyperlipidemi, dibetes, smoking, estimted glomerulr filtrtion rte, C-rective protein, hemoglobin, men corpusculr volume, nd nutritionl fctors (folte, iron nd vitmin B 12 ) deficiencies with ech unit (0.1) increse in RDW. Upon receiver-operting chrcteristics nlysis, the predictive ccurcy of the Americn College of Crdiology / Americn Hert Assocition (ACC/AHA)-defined PAD screening criteri (for high-risk popultion) ws t best, but improved significntly (0.727) fter ddition of RDW (p < ). In conclusion, higher levels of RDW re independently ssocited with higher risk of PAD nd cn significntly improve the risk prediction beyond tht estimted by ACC/AHA-defined PAD screening criteri. Keywords peripherl rtery disese; RDW Introduction Red cell distribution width (RDW) is routinely reported in utomted complete blood counts (CBC) nd hs trditionlly been used to differentite vrious types of nemi. 1 The evidence ssociting RDW with higher risk of mortlity hs been expnding since the initil report of its prognostic utility in hert filure ptients. 2 RDW hs lso been shown to independently predict overll nd crdiovsculr (CV) mortlity in the generl popultion nd vrious high-risk popultions. 3 7 We recently reported RDW to be strongly ssocited with higher 10-yer estimted risk of coronry hert disese (CHD) events in predominntly helthy, low-risk generl popultion, free of prior history of CV events nd dibetes. 8 From the dt evluting the ssocition between RDW nd mortlity in hert filure ptients, Felker et l. 2 suggested the possibility of RDW being n integrted mrker of severl underlying pthophysiologicl processes such s nutritionl deficiencies, renl dysfunction, heptic congestion nd inflmmtory stress. Subsequent reserch showed RDW to be strongly ssocited with mrkers of chronic subclinicl inflmmtion, higher oxidtive stress, under-nutrition, nd bet-ntriuretic peptide (BNP). 9,10 Our group lso demonstrted tht RDW ws strongly nd Division of Crdiology, Deprtment of Internl Medicine, Detroit Medicl Center/Wyne Stte University, Detroit, MI, USA Corresponding uthor: Luis Afonso Internl Medicine Division of Crdiology Wyne Stte University Detroit, MI USA Emil: lfonso@med.wyne.edu

2 156 Vsculr Medicine 17(3) independently ssocited with microlbuminuri, mrker of generlized endothelil dysfunction, in ntionlly representtive cohort. 11 RDW is esily mesured, stndrdized nd typiclly reported with complete blood count vlues t no dditionl cost; its independent predictive vlue for vrious CV events mkes further reserch of other t-risk popultions for CV events impertive. Peripherl rtery disese (PAD), now widely considered CHD risk equivlent, is one such condition. PAD is preceded by higher levels of chronic subclinicl inflmmtion, endothelil dysfunction nd oxidtive stress There is n incresing effort to identify novel biomrker or set of biomrkers to effectively chrcterize individuls with or without PAD. Mrkers of inflmmtion (C-rective protein (CRP), interleukin-6 (IL-6), etc.), endothelil dysfunction (soluble cell dhesion molecules, von Willebrnd fctor, etc.) nd oxidtive stress (homocysteine (Hcy), isoprostnes, etc.) hve been shown to be ssocited with PAD. 12,15 17 To our knowledge, no prior study hs explored the ssocition between RDW nd PAD. Therefore, in this crosssectionl cohort of the Ntionl Helth nd Nutrition Exmintion Survey (NHANES), we sought to evlute the ssocition between RDW nd PAD. Contingent upon the results, we further sought to compre the clinicl utility of RDW in identifying those t risk of PAD propos the currently recommended Americn College of Crdiology / Americn Hert Assocition (ACC/AHA) PAD screening guidelines. 18 Methods Study popultion NHANES is cross-sectionl survey of non-institutionlized civilin cohort of ntionlly representtive individuls. We nlyzed prticipnts of the NHANES, who underwent stndrdized interviews, physicl exmintion nd lbortory testing long with nkle brchil index (ABI) mesurement. The study protocols for NHANES received the Ntionl Center for Helth Sttistics ethics/ institutionl review bord pprovl. 19 Dt collection Dt on ABI were vilble for totl of 7571 individuls, from which the study ws conducted mong prticipnts ged 40 yers of older (n = 6950), fter excluding those with missing vlues on RDW (n = 218), those with ABI vlues > 1.4 (n = 70) nd other study vribles (n = 333). A stndrdized procedure protocol ws followed t ll study sites by trined personnel. Dt were collected for demogrphic vribles such s ge, sex, nd ethnicity (selfreported) nd for medicl co-morbidities such s hypertension (defined s blood pressure 140/90 or use of nti-hypertensive medictions or physicin dignosis of hypertension) nd dibetes mellitus (DM) (defined s physicin dignosis of DM, tking orl hypoglycemics or insulin for DM, or non-fsting plsm glucose 11.1 mmol/l (200 mg/dl) or fsting plsm glucose 7 mmol/l (126 mg/dl), or hemoglobin (Hgb) A1c 6.5). Dt were lso collected for ever smoking > 100 cigrettes during lifetime, hyperlipidemi (dignosed by physicin or serum totl cholesterol 240 mg/dl or use of lipid-lowering therpy), body mss index (BMI; kg/m 2 ) (norml (BMI < 25), overweight (BMI ), nd obese (BMI 30)), nd comorbidities (self-reported) such s coronry rtery disese (CAD), myocrdil infrction (MI), stroke, ngin, nti-hypertension mediction use nd fmily history of MI. 20 Ankle brchil index mesurement PAD, s defined by ABI, ws the primry outcome vrible of the study. For prticipnts with 1 rm nd weight < 400 lb (181.5 kg), the systolic blood pressure (SBP) ws mesured using blood pressure cuffs on the right brchil rtery nd both posterior tibil rteries with n 8-MHz Doppler probe. Two mesurements t ech site were tken nd verged for prticipnts ged yers, wheres one mesurement ws tken for prticipnts ged 60 yers. For those with conditions precluding mesurement of the right rm, the left brchil rtery SBP ws tken. The ABI ws clculted s the rtio of the verge nkle SBP to rm SBP. 20 The lower of the two mesurements ws considered the ABI for the present study. PAD ws defined s ABI < 0.9 nd prticipnts with n ABI greter thn 1.4 were excluded. ACC/AHA screening criteri for PAD Current ACC/AHA guidelines recommend screening certin high-risk groups using ABI (clss ІB ). Recommendtions to perform ABI include those individuls ged less thn 50 yers with history of dibetes nd one other therosclerosis risk fctor (smoking, dyslipidemi, hypertension, or hyperhomocysteinemi); those ged between 50 nd 69 yers with history of smoking or dibetes; those ged 70 yers nd older; those with leg symptoms upon exertion (suggestive of cludiction) or ischemic rest pin; those with n bnorml lower-extremity pulse exmintion; nd those with known therosclerotic coronry, crotid, or renl rtery disese 18 (Tble 1). Lbortory mesurements RDW, Hgb nd men corpusculr volume (MCV) were mesured using the Beckmn utomted Coulter counter method in combintion with n utomtic diluting nd mixing device for smple processing, nd single-bem photometer for hemoglobinometry. 20 High-sensitivity C-rective protein (hs-crp) ws mesured using ltexenhnced nephelometry, HbA1c by high-performnce liquid chromtogrphy (HPLC) nd plsm Hcy by fully utomted fluorescence polriztion immunossy (FPIA; Abbott Dignostics). 20 Serum cretinine ws stndrdized by the following formul: 1.013*serum cretinine (mg/dl)

3 Zlwdiy SK et l. 157 Tble 1. Receiver-opertive chrcteristics (ROC) nlysis compring re under the curve (AUC) for individul risk ctegories with nd without RDW for peripherl rtery disese Risk fctor ctegories AUC not including RDW AUC including RDW Improvement in ROC AUC A Age < 50 yers with dibetes nd one other therosclerosis < risk fctor (smoking, dyslipidemi, hypertension, or hyperhomocysteinemi) B Age yers nd history of smoking or dibetes < C Age 70 yers nd older < D Known therosclerotic coronry, crotid or renl rtery disese < E Combintion of criteri A through D < Peripherl rtery disese is defined s nkle brchil index < The estimted glomerulr filtrtion rte (egfr) (ctegorized s egfr 60 vs egfr < 60) ws then mesured using the formul suggested by the Modifiction of Diet in Renl Disese study eqution. 21 Iron deficiency ws defined s the prticipnts meeting t lest two of the following three criteri: trnsferrin sturtion < 15%, serum ferritin level < 12 ng/ml, nd erythrocyte protoporphyrin level > 69.8 μm. 22 Additionlly, vitmin B 12 deficiency ws defined s serum B 12 level < 200 pg/dl, wheres folic cid deficiency ws defined s serum folic cid < 2.6 ng/ml or red blood cell folte level < ng/ml. Urine cretinine ws nlyzed by Jffe rection nd urinry lbumin ws mesured using solid-phse fluorescent immunossy. 20 The urine lbumin cretinine rtio (mg/g) ws clculted by dividing the urinry lbumin vlue by the urinry cretinine concentrtion. Microlbuminuri ws defined s urine lbumin/cretinine rtio (ACR) 30 mg/g. Detiled dt on the NHANES opertions re vilble on the NHANES website ( nhnes_questionnires.htm). Sttisticl nlysis We nlyzed RDW both s continuous nd ctegoricl vrible (in qurtiles; bsed on its distribution mong prticipnts without PAD). Bseline chrcteristics were compred cross these qurtiles using the chi-squre test for ctegoricl vribles (%) nd the nlysis of vrince test for continuous vribles (men ± SD). Hs-CRP nd Hcy were log-trnsformed to normlize their distribution. The primry im of the study ws to ssess whether RDW is independently ssocited with prevlent PAD beyond the risk fctors proposed by ACC/AHA guidelines. Additionlly, we sought to evlute whether vribles such s Hgb, MCV, deficiency of nutritionl fctors or inflmmtory mrkers like CRP nd the presence of renl dysfunction served s confounders or effect modifiers for the ssocition of RDW with PAD. Therefore, the following multivrible djusted logistic regression models were generted: Model 1 nlysis of RDW nd PAD djusted for ge, sex, rce, BMI, hypertension, DM, hyperlipidemi, smoking, egfr, hs-crp, blood Hgb nd MCV levels; Model 2 djusted for vribles in Model 1 + history of CV disese, history of congestive hert filure, fmily history of CHD, men pltelet volume; nd Model 3 vribles in Model 2 djusted for deficiencies of serum iron, folte nd vitmin B 12 (nlysis excludes observtions (n = 976) with missing informtion on bove nutrients). Forml sttisticl nlysis for the interction between vrious independent vribles with RDW ws lso performed, which ws found to be sttisticlly non-significnt. A grphicl plot ws generted ssessing the predicted probbility nd observed rte of prevlent PAD ginst RDW vlues. To further evlute for the ssocition between RDW nd levels of ABI vlues, we performed Person s correltion nlysis fter excluding those with the missing informtion on nutritionl fctors nd those with extreme RDW elevtions (RDW > 17; n = 80). Upon identifying RDW to be significntly ssocited with prevlent PAD, we sought to evlute whether it dded to the predictive ccurcy of ACC/AHA recommended criteri for pursuing work-up for PAD. Therefore, we performed receiver-operting chrcteristics (ROC) nlysis which tests the generl discrimintive power of dignostic test using sensitivity (Se) nd specificity (Sp) prmeters over the whole rnge of testing vlues nd lso provides re under the curve (AUC) which indictes dignostic power of the test. We compred the dignostic ccurcy of RDW for PAD risk prediction to tht of ACC/ AHA-defined screening criteri. Six-yer smple weights provided by the Ntionl Center for Helth Sttistics were used in ll nlyses to incorporte the complex survey design of NHANES with pproprite reflections of strtifiction nd clustering. Sttisticl significnce ws defined s p-vlue < 0.05 for the entire nlysis. All nlyses were performed using sttisticl softwre STATA, version 10 (STATA Corp LP, College Sttion, TX, USA). Results Significnt differences were observed in bseline chrcteristics distribution cross the RDW qurtiles (Tble 2). There ws grded increse in the proportion of ptients with comorbidities such s CAD, hypertension, DM, MI, stroke nd ngin, nd microlbuminuri with incresing qurtiles of RDW (p < 0.001). Similrly, there ws grded increse in men vlues for ge, SBP, HbA1c, hs-crp, Hcy nd serum cretinine (p for trend < 0.001). In contrdistinction, men levels of Hgb, MCV nd egfr decresed with incresing qurtiles of RDW (p for trend < 0.001). The proportion of

4 158 Vsculr Medicine 17(3) Tble 2. Bseline chrcteristics of the study cohort (Ntionl Helth nd Nutrition Exmintion Survey, ) RDW qurtiles (n = 6950) p-vlue Q n = 1896 Q n = 1417 Q n = 1522 Q n = 2115 Age, yers 56.5 ± ± ± ± 13.4 < Mles, % Rce, % Africn Americn Hispnic Americn Cucsin Americn Other Americn < Coronry rtery disese, % < Dibetes, % < MI, % < Stroke, % < Angin, % < Smoking (> 100 cigrettes in lifetime) Fmily history of MI Systolic blood pressure, mmhg 128 ± ± ± ± 22 < Anti-hypertension mediction use, % < Body mss index Overweight < Obese Blood hemoglobin, g/dl 14.7 ± ± ± ± 1.6 < Men corpusculr volume, μm ± ± ± ± 7.2 < Totl cholesterol, mg % 210 ± ± ± ± Serum high-density lipoprotein, mg % 53 ± ± ± ± Hemoglobin A1c, % 5.6 ± ± ± ± 1.2 < Stndrdized serum cretinine, mg % 1.0 ± ± ± ± 0.7 < Estimted GFR, ml/min/1.73 m 2 73 ± ± ± ± 20 < High-sensitivity C-rective protein, mg/dl 0.36 ± ± ± ± 1.19 < Homocysteine, μmol/l 8.8 ± ± ± ± 6.4 < Ankle brchil index (< 0.9) < Iron deficiency, % < Folte deficiency, % < Vitmin B 12 deficiency, % b Urine microlbuminuri, % < Smple size excluded missing vlues on deficiencies of iron, folic cid nd vitmin B 12 (n = 5974). b Smple size excluded individuls with mcrolbuminuri (n = 2767). RDW, red cell distribution width; MI, myocrdil infrction; GFR, glomerulr filtrtion rte. Africn Americns incresed nd the proportion of Cucsin Americns decresed with incresing RDW qurtiles (p < 0.001). Blood levels of lipids (e.g. totl cholesterol nd highdensity lipoprotein) exhibited non-grded difference in men levels cross RDW qurtiles. The proportion of individuls with PAD incresed significntly s the RDW qurtile incresed (4.22% in Q1 vs 13.90% in Q4; p < 0.001) (Tble 3). The odds of hving PAD incresed by 19% with ech unit (0.1) increse in RDW (95% confidence intervl (CI): ; p = 0.003) fter djustments shown in Model 3 (Tble 3). Similr results were obtined when RDW ws evluted in ctegories (Tble 3). The interction term between RDW nd co-vrites for PAD risk prediction ws found to be sttisticlly nonsignificnt (ge (< 70 vs 70; p = 0.94), sex (p = 0.94), dibetes (p = 0.23), hypertension (p = 0.83), renl impirment (p = 0.052), history of therosclerotic diseses (p = 0.27), nutritionl fctors deficiency (p = 0.509) nd ethnicities (p > 0.05 for ll)). Figure 1 shows the reltionship between the predicted nd observed rte for probbility of PAD with incresing RDW vlues; s shown, there ppers to be liner reltionship between the two. Similrly, Figure 2 shows the ssocition between RDW vlues nd ABI vlues s continuous vribles; s shown, sttisticlly significnt liner negtive ssocition is pprent (Person s rho = 0.18; p < 0.001). Figure 3A shows the results of multivrite logistic regression nlysis evluting the independent role of RDW in PAD risk prediction beyond tht conferred by trditionl risk fctors outlined in the ACC/AHA guidelines. It is worth noting tht we lso performed nlyses presented

5 Zlwdiy SK et l. 159 Tble 3. Red cell distribution width nd overll risk of prevlent peripherl rtery disese A: RDW s continuous vrible (for ech 0.1 increse) OR [95% CI]; p-vlue Model [ ]; < Model [ ]; Model [ ]; B: RDW qurtiles (n) Rnge Q1 (1896) 12.2 Q2 (1417) Q3 (1522) Q4 (2115) 13.1 Cse (%) 80 (4.22%) 87 (6.14%) 157 (10.32%) 294 (13.90%) OR [95% CI]; p-vlue OR [95% CI]; p-vlue OR [95% CI]; p-vlue Model 1 ref [ ]; [ ]; [ ]; < Model 2 ref [ ]; [ ]; [ ]; Model 3 ref [ ]; [ ]; [ ]; Model 1: RDW djusted for ge, sex, rce, body mss index, hypertension, dibetes, hyperlipidemi, smoking, estimted glomerulr filtrtion rte nd high-sensitivity C-rective protein, blood hemoglobin nd men corpusculr volume levels. Model 2: Model 1 + history of crdiovsculr disese, history of congestive hert filure, fmily history of coronry hert disese, men pltelet volume. Model 3 : Model 2 + deficiencies of serum iron, folte nd vitmin B 12. Anlysis is done for totl smple size of 5974 individuls. RDW, red cell distribution width; OR, odds rtio; CI, confidence intervl. Figure 1. The reltionship between RDW vlues nd expected versus observed rte of hving prevlent PAD mong Ntionl Helth nd Nutrition Exmintion Survey prticipnts in Tbles 1 nd 2 using Hcy s co-vrite in Models 2 nd 3; we did not observe ny chnge in the strength of ssocition between RDW nd PAD upon djustment for Hcy (dt not shown). Tble 1 nd Figure 3B show results of the ROC nlysis compring the predictive ccurcy (AUC) provided by RDW nd the ACC/AHA-defined screening criteri for high-risk popultion t risk of PAD (individul criteri nd overll combintion) lone nd in combintion. The overll predictive ccurcy of the ACC/AHA-defined criteri (risk ctegory E in Tble 1) ws 0.657, which improved significntly (to 0.727) fter the ddition of RDW. Similrly, individul risk ctegories for those less thn 70 yers of ge (defined by ACC/AHA) provided poor predictive ccurcy for identifying those t risk of PAD (AUC of for ctegory A nd for ctegory B; Tble 1), which improved significntly fter ddition of RDW to the model (AUC of for both ctegory A nd B; p-vlue for improvement in AUC < 0.001) (Tble 1). RDW improved the AUC for ll the individul risk ctegories; lthough, the mgnitude of increse ws greter mong those under the ge of 70 yers (Tble 1).

6 160 Vsculr Medicine 17(3) Figure 2. Person s correltion between RDW nd nkle brchil index vlues mong Ntionl Helth nd Nutrition Exmintion Survey prticipnts Discussion In this study, we systemticlly evluted the potentil ssocition between RDW nd prevlent PAD for the first time. The following conclusions my be drwn from our nlysis: (1) RDW is strongly ssocited with PAD with grded increse in prevlence cross qurtiles of incresing RDW; (2) higher RDW is ssocited with PAD independent of sex, DM, hypertension, nd deficiency of nutritionl fctors; (3) RDW is independently ssocited with PAD in prticipnts of ll the ethnicities nd prticipnts with/without renl dysfunction, though the ssocition ws pprently stronger in Africn Americns, Cucsin Americns nd prticipnts without renl dysfunction; nd (4) RDW significntly improved the risk prediction offered by current ACC/AHA-defined screening guidelines for highrisk popultion. RDW is n emerging mrker, with published dt supporting its role in predicting survivl in vrious crdiovsculr conditions. 2 6 However, no prior study hs evluted the ssocition between RDW nd PAD in ntionlly representtive smple of multi-ethnic individuls. We observed n RDW 13% (Q4) to be ssocited with 79% higher odds of hving PAD (95% CI: ; p < 0.001) fter djustments for renl function, hs-crp nd Hgb level in ddition to demogrphic vribles, co-morbidities nd nutritionl deficiencies. Additionlly, upon strtifying the cohort bsed on deficiency sttus of nutritionl fctors, renl function, hypertension, dibetes, sex nd ethnicity, RDW emerged s n independent predictor of PAD (Tble 1). Comprble results were reported by Ptel et l. 3 nd Perlstein et l. 5 who showed RDW to be ssocited with ll-cuse nd crdiovsculr mortlity upon similr djustments in cohort of NHANES-ІІІ study prticipnts. The novelty of our study findings is tht we observed higher RDW to be positively ssocited with higher risk of prevlent PAD in grded mnner, rising the potentilly significnt utility of RDW s novel biomrker for PAD. The precise pthobiologic mechnisms for the ssocition between RDW nd vrious crdiovsculr diseses re yet to be elucidted, lthough the potentil role of oxidtive stress, chronic inflmmtion nd endothelil dysfunction wrrnts considertion. During their verge lifespn of 120 dys, red blood cells (RBCs) re exposed to vriety of hrmful insults tht rnge from mechnicl nd oxidtive to hyperosmotic stress. 23 They re directly involved in the regultion of rective oxygen nd nitrogen species delivery to peripherl tissue, thereby modulting the cycle of oxidtive dmge. 24 It hs been hypothesized from experimentl studies tht RBCs hve free rdicl scvenging (the presence of n bundnt mount of powerful nti-oxidnt enzymes which help control oxidtive stress under norml physiologicl conditions) nd pro-oxidnt (redox imblnce in RBCs resulting from overwhelming oxidtive dmge nd inflmmtion in pthologicl tissues which lters nd overcomes the nti-oxidnt mechnisms nd, therefore, RBCs function s pro-oxidnt cells modifying nd regulting distnt vsculr beds nd endothelil function) nd signling properties (oxidtive stress cusing ltertion in RBC membrne properties nd the interction mong RBCs nd between RBCs nd other cells which leds to perpetution of oxidtive dmge). 25,26 Oxidtive stress cn led to cytoskeleton rerrngement nd loss of lipid symmetry in RBC membrnes leding RBCs to become more rigid nd symmetric in size nisocytosis. 27 It hs been shown tht oxidized RBCs hve higher ggregbility nd dhesiveness to the endothelil tissue leding to vicious cycle of oxidtive dmge-induced

7 Zlwdiy SK et l. 161 Figure 3. Vlue of red cell distribution width (RDW) for peripherl rtery disese (PAD) risk prediction: (A) multivrite logistic regression model demonstrting significnt risk fctors for PAD; (B) receiver-opertive chrcteristics nlysis compring the predictive ccurcy (re under the curve (AUC)) of Americn College of Crdiology/Americn Hert Assocition-defined high-risk group nd RDW lone nd in combintion, for the dignosis of subjects with nkle brchil index < 0.9 (p-vlue for improvement AUC by including RDW to high-risk groups < 0.001) endothelil dysfunction. 28 In this context, we observed n independent ssocition between RDW nd microlbuminuri well-estblished mrker of generlized endothelil dysfunction in the generl US popultion free of prior history of CV disese. 11 Similrly, in the current study, we gin noted tht the proportion of prticipnts with microlbuminuri incresed significntly with higher RDW qurtiles (19% in Q1 vs 36% in Q4; p for trend < 0.001). The ssocition of higher RDW with mrkers of oxidtive stress, 10 endothelil dysfunction 11 nd chronic inflmmtion 9 underscore the importnce of RDW s rel-time integrtive biomrker of generlized therosclerotic burden. In this context, the incrementl ssocition of higher RDW with higher risk of PAD found in our study

8 162 Vsculr Medicine 17(3) emphsizes the clinicl relevnce of this biomrker. Whether RDW hs differentil ssocition with pthophysiologicl processes going on in different vsculr beds, is subject of future reserch. RDW nd ACC/AHA screening guidelines for high-risk popultion According to the current ACC/AHA guidelines, it is deemed pproprite to consider mesuring the ABI in high-risk subgroups (Tble 1) t risk of PAD. 18 Although the current recommendtions re bsed on epidemiologicl studies only, to dte no prior study hs nlyzed the predictive utility of these screening criteri in the generl popultion, especilly one representing multi-ethnic US generl popultion. As our nlysis reveled RDW to hve n independent predictive vlue beyond the estblished ACC/AHA-defined screening criteri, we further ttempted to explore the incrementl vlue of RDW over these criteri. We observed significnt improvement in the predictive ccurcy of currently recommended screening criteri with the ddition of RDW (vlues > 13) for the identifiction of individuls with PAD (Tble 1). Since RDW is redily vilble s prt of the routine complete blood count, nd is esily reproducible nd cost-effective, it could be potentilly utilized longside recommended screening criteri to finesse PAD risk prediction. Our study suffers from the inherent limittions of cross-sectionl nlysis, restricting our efforts to evlution of prevlent rther thn incident PAD. Further studies with prospective follow-up will be needed to exmine the temporl reltionship between RDW with incident PAD. The observed weker ssocition between RDW nd PAD in ptients with renl impirment ppers to be secondry to the reltively smll smple nd event size in tht subgroup. This dtbse lso lcked seril mesurements of RDW, which might hve provided further insight into its ssocition with PAD severity. Misclssifiction of PAD my lso hve occurred, s NHANES did not follow current recommended guidelines for ABI mesurements. 18 However, prior studies utilizing ABI mesurements from this dtbse hve contributed criticl informtion leding to significnt dvnces in the understnding of PAD We lcked dt on crdiovsculr mortlity nd thus were unble to explore the effect modifiction of RDW, if ny, on the ssocition between PAD nd crdiovsculr outcomes. Additionlly, the cross-sectionl nture of NHANES precludes conclusions bout direction or cuslity of ssocitions observed in the present study. Despite these limittions, our study does hve the strengths of lrge, multi-ethnic smple of ntionlly representtive individuls, in ddition to wide rry of dt collected by stndrdized protocols dhering to rigorous qulity control. Pending dditionl reserch, our findings should be viewed s preliminry nd serve s bsis for future studies evluting the cusl nd temporl reltionships between RDW, PAD nd crdiovsculr outcomes. Conclusion Our novel observtions suggest strong nd independent reltionship between RDW with PAD. These findings re prticulrly noteworthy, s RDW ppers to be n emerging, cost-effective biomrker, which could potentilly help optimize the predictive ccurcy of the ACC/AHA currently recommended screening guidelines imed t identifying individuls t risk for PAD. Funding This reserch received no specific grnt from ny funding gency in the public, commercil, or not-for-profit sectors. Conflict of interest The contents re solely the responsibility of the uthors nd do not represent the officil view of ny orgniztions. The uthors hve no conflicts of interest or finncil disclosures to report. References 1. Tefferi A, Hnson CA, Inwrds DJ. How to interpret nd pursue n bnorml complete blood cell count in dults. Myo Clin Proc 2005; 80: Felker GM, Allen LA, Pocock SJ, et l. Red cell distribution width s novel prognostic mrker in hert filure: dt from the CHARM Progrm nd the Duke Dtbnk. J Am Coll Crdiol 2007; 50: Ptel KV, Ferrucci L, Ershler WB, Longo DL, Gurlnik JM. Red blood cell distribution width nd the risk of deth in middle-ged nd older dults. Arch Intern Med 2009; 169: Ptel KV, Semb RD, Ferrucci L, et l. Red cell distribution width nd mortlity in older dults: met-nlysis. J Gerontol A Biol Sci Med Sci 2010; 65: Perlstein TS, Weuve J, Pfeffer MA, Beckmn JA. Red blood cell distribution width nd mortlity risk in community-bsed prospective cohort. Arch Intern Med 2009; 169: Tonelli M, Scks F, Arnold M, Moye L, Dvis B, Pfeffer M. Reltion between red blood cell distribution width nd crdiovsculr event rte in people with coronry disese. Circultion 2008; 117: Zlwdiy SK, Zmily H, Frh J, Difllh S, Ali O, Ghli JK. Red cell distribution width nd mortlity in predominntly Africn-Americn popultion with decompensted hert filure. J Crd Fil 2011; 17: Zlwdiy SK, Veernn V, Nirj A, Prdhn J, Afonso L. Red cell distribution width nd risk of coronry hert disese events. Am J Crdiol 2010; 106: Forhecz Z, Gombos T, Borguly G, Pozsonyi Z, Prohszk Z, Jnoskuti L. Red cell distribution width in hert filure: prediction of clinicl events nd reltionship with mrkers of ineffective erythropoiesis, inflmmtion, renl function, nd nutritionl stte. Am Hert J 2009; 158: Allen LA, Felker GM, Mehr MR, et l. Vlidtion nd potentil mechnisms of red cell distribution width s

9 Zlwdiy SK et l. 163 prognostic mrker in hert filure. J Crd Fil 2010; 16: Afonso L, Zlwdiy SK, Veernn V, Pnich SS, Nirj A, Jcob S. Reltionship between red cell distribution width nd microlbuminuri: popultion-bsed study of multiethnic representtive US dults. Nephron Clin Prct 2011; 119: c277 c Loffredo L, Mrcocci A, Pigntelli P, et l. Oxidtivestress-medited rteril dysfunction in ptients with peripherl rteril disese. Eur Hert J 2007; 28: Beckmn JA, Preis O, Ridker PM, Gerhrd-Hermn M. Comprison of usefulness of inflmmtory mrkers in ptients with versus without peripherl rteril disese in predicting dverse crdiovsculr outcomes (myocrdil infrction, stroke, nd deth). Am J Crdiol 2005; 96: Wildmn RP, Muntner P, Chen J, Sutton-Tyrrell K, He J. Reltion of inflmmtion to peripherl rteril disese in the ntionl helth nd nutrition exmintion survey, Am J Crdiol 2005; 96: Ridker PM, Cushmn M, Stmpfer MJ, Trcy RP, Hennekens CH. Plsm concentrtion of C-rective protein nd risk of developing peripherl vsculr disese. Circultion 1998; 97: Tzoulki I, Murry GD, Lee AJ, Rumley A, Lowe GD, Fowkes FG. C-rective protein, interleukin-6, nd soluble dhesion molecules s predictors of progressive peripherl therosclerosis in the generl popultion: Edinburgh Artery Study. Circultion 2005; 112: Krzyznowsk K, Mittermyer F, Krugluger W, et l. Asymmetric dimethylrginine is ssocited with mcrovsculr disese nd totl homocysteine in ptients with type 2 dibetes. Atherosclerosis 2006; 189: Hirsch AT, Hskl ZJ, Hertzer NR, et l. ACC/AHA 2005 Prctice Guidelines for the mngement of ptients with peripherl rteril disese (lower extremity, renl, mesenteric, nd bdominl ortic): collbortive report from the Americn Assocition for Vsculr Surgery/Society for Vsculr Surgery, Society for Crdiovsculr Angiogrphy nd Interventions, Society for Vsculr Medicine nd Biology, Society of Interventionl Rdiology, nd the ACC/AHA Tsk Force on Prctice Guidelines (Writing Committee to Develop Guidelines for the Mngement of Ptients With Peripherl Arteril Disese): endorsed by the Americn Assocition of Crdiovsculr nd Pulmonry Rehbilittion; Ntionl Hert, Lung, nd Blood Institute; Society for Vsculr Nursing; TrnsAtlntic Inter-Society Consensus; nd Vsculr Disese Foundtion. Circultion 2006; 113: e NCHS Reserch Ethics Review Bord (ERB) pprovl. Centers for Disese Control nd Prevention (CDC), Ntionl Center for Helth Sttistics (NCHS). Avilble t: gov/nchs/nhnes/irb98.htm (ccessed 15 Mrch 2010). 20. Centers for Disese Control nd Prevention (CDC). Ntionl Center for Helth Sttistics (NCHS). Ntionl Helth nd Nutrition Exmintion Survey Questionnire (or Exmintion Protocol, or Lbortory Protocol). Hyttsville, MD: US Deprtment of Helth nd Humn Services, Centers for Disese Control nd Prevention, [ gov/nchs/nhnes/nhnes_questionnires.htm]. 21. Levey AS, Coresh J, Greene T, et l. Using stndrdized serum cretinine vlues in the modifiction of diet in renl disese study eqution for estimting glomerulr filtrtion rte. Ann Intern Med 2006; 145: Looker AC, Dllmn PR, Crroll MD, Gunter EW, Johnson CL. Prevlence of iron deficiency in the United Sttes. JAMA 1997; 277: Crwford JH, Chcko BK, Kevil CG, Ptel RP. The red blood cell nd vsculr function in helth nd disese. Antioxid Redox Signl 2004; 6: Comporti M, Signorini C, Buonocore G, Ciccoli L. Iron relese, oxidtive stress nd erythrocyte geing. Free Rdic Biol Med 2002; 32: Yelinov V, Glzchev Y, Khrmtsov V, Kudryshov L, Rykov V, Slgnik R. Studies of humn nd rt blood under oxidtive stress: chnges in plsm thiol level, ntioxidnt enzyme ctivity, protein crbonyl content, nd fluidity of erythrocyte membrne. Biochem Biophys Res Commun 1996; 221: Minetti M, Agti L, Mlorni W. The microenvironment cn shift erythrocytes from friendly to hrmful behvior: pthogenetic implictions for vsculr diseses. Crdiovsc Res 2007; 75: Minetti M, Mlorni W. Redox control of red blood cell biology: the red blood cell s trget nd source of prooxidnt species. Antioxid Redox Signl 2006; 8: Berliner S, Rogowski O, Ahronov S, et l. Erythrocyte dhesiveness/ggregtion: novel biomrker for the detection of low-grde internl inflmmtion in individuls with therothrombotic risk fctors nd proven vsculr disese. Am Hert J 2005; 149: Pnde RL, Perlstein TS, Beckmn JA, Creger MA. Assocition of insulin resistnce nd inflmmtion with peripherl rteril disese: the Ntionl Helth nd Nutrition Exmintion Survey, 1999 to Circultion 2008; 118: O Hre AM, Glidden DV, Fox CS, Hsu CY. High prevlence of peripherl rteril disese in persons with renl insufficiency: results from the Ntionl Helth nd Nutrition Exmintion Survey Circultion 2004; 109: Selvin E, Erlinger TP. Prevlence of nd risk fctors for peripherl rteril disese in the United Sttes: results from the Ntionl Helth nd Nutrition Exmintion Survey, Circultion 2004; 110: