the louisiana state university health care services division ( lsuhcsd ) operates seven public hospitals and affiliated clinics in louisiana that provide quality medical care to the residents of louisiana regardless of their income or insurance coverage ( 1924 ) .
overall , lsuhcsd facilities have served ~1.6 million patients ( 35% of the louisiana population ) since 1997 .
administrative , anthropometric , laboratory , clinical diagnosis , and medication data collected at these facilities are available in electronic form for both inpatients and outpatients from 1997 . using these data ,
a cohort of patients with diabetes was established by using the icd-9 ( code 250 ) through the lsuhls database between 1 january 1999 and 31 december 2009 . both inpatients and outpatients
internal diabetes disease - management guidelines call for physician confirmation of diabetes diagnoses by applying the american diabetes association criteria : a fasting plasma glucose level 126 mg / dl , 2-h glucose level 200 mg / dl after a 75-g 2-h oral glucose tolerance test , and one or more classic symptoms plus a random plasma glucose level 200 mg / dl ( 25 )
. the first record of diabetes diagnosis was used to establish the baseline for each patient in the present analyses owing to the design of the cohort study . before diagnosed with diabetes ,
the agreement of diabetes diagnosis was 97% : 20,919 subjects of a sample of 21,566 hospital patients with discharge diagnoses based on icd codes also had physician - confirmed diabetes by using the american diabetes association diabetes diagnosis criteria ( 25 ) .
the current study included 35,368 patients with newly diagnosed diabetes ( 15,560 white and 19,808 african american ) who were 3094 years of age without a history of lea and with complete repeated data on all risk factor variables . in these patients with diabetes ,
~77.3% qualify for free care ( by virtue of being low income and uninsured  any individual or family unit whose income is 200% of federal poverty level ) , ~4.9% of patients are self - pay ( uninsured , but incomes not low enough to qualify for free care ) , ~5.2% of patients are covered by medicaid , ~10.4% of patients have medicare , and ~2.2% of patients are covered by commercial insurance .
the study and analysis plan were approved by both the pennington biomedical research center and louisiana state university health sciences center institutional review boards .
we did not obtain informed consent from participants involved in our study because we used anonymized data compiled from electronic medical records .
the patient s characteristics , including age of diabetes diagnosis , sex , race / ethnicity , family income , smoking status , types of health insurance , body weight , height , bmi , blood pressure , total cholesterol , hdl cholesterol , ldl cholesterol , triglycerides , hba1c , estimated glomerular filtration rate ( egfr ) , history and incidence of peripheral arterial disease , ulcer , and foot deformity , and medication ( antihypertensive drugs , cholesterol - lowering drugs , and antidiabetes drugs ) within half a year after the diabetes diagnosis ( baseline ) and during follow - up after the diabetes diagnosis ( follow - up ) , were extracted from the computerized hospitalization records .
foot risk factors were identified using icd-9 codes based on existing literature ( 26,27 ) , which included peripheral arterial disease ( icd-9 codes 443.81 , 440.2 , 440.20 , 440.21 , 440.22 , 440.23 , 440.24 , 440.29 , 440.8 , 440.9 , 442.2 , 442.3 , 443.0 , 443.1 , 443.81 , 443.89 , 443.9 , 444.22 , 444.81 , 2507.x , and 785.4 ) , ulcer ( icd-9 codes 707.1x and 707.9 ) , and foot deformity ( icd-9 codes 94.0 , 713.5 , 727.1 , 735.0 , 735.2 , and 735.4735.9 ) .
the updated mean values of hba1c , ldl cholesterol , bmi , blood pressure , and egfr over time were measured first at baseline and second as an updated mean of annual measurement , calculated for each participant from baseline to each year of follow - up . for example , at 1 year the updated mean is the average of the baseline and 1-year values and at 3 years it is the average of baseline , 1-year , 2-year , and 3-year values . in case of an event during follow - up , the period for estimating updated mean value was from baseline to the year before this event occurred ( 10,28 ) .
the average number of hba1c measurements during the follow - up period was 7.4 times .
follow - up information was obtained from the lsuhls inpatient and outpatient database by using the unique number assigned to every patient who visits the lsuhcsd hospitals .
the diagnosis of lea was the primary end point of interest of the study and was defined according to the icd-9 ( codes 84.1084.17 ) .
since 1997 , diagnoses of lea were made by the treating physicians based on a clinical assessment and examinations as considered relevant by the clinician in charge of treatments .
follow - up of each cohort member continued until the date of the diagnosis of lea , the date of the last visit if the subject stopped use of lsuhcsd hospitals , death , or 31 may 2012 .
the association between hba1c and the risk of lea was analyzed by using cox proportional hazards models .
hba1c was evaluated in the following two ways : 1 ) as six categories ( hba1c < 6.0% [ 42 mmol / mol ] [ reference group ] , 6.06.9% [ 4252
mmol / mol ] , 7.07.9% [ 5363 mmol / mol ] , 8.08.9% [ 6474 mmol / mol ] , 9.09.9% [ 7585 mmol / mol ] , and 10.0% [ 86 mmol / mol ] ) and
different levels of hba1c were included in the models as dummy variables , and the significance of the trend over different categories of hba1c was tested in the same models by giving an ordinal numerical value for each dummy variable .
all analyses were adjusted for age and sex and further for smoking , income , types of insurance , bmi , systolic blood pressure , ldl cholesterol , egfr , peripheral arterial disease , ulcer , and foot deformity at baseline and during follow - up , use of antihypertensive drugs , use of diabetes medications , and use of cholesterol - lowering agents .
when we analyzed the association between updated mean of hba1c and lea risk , we adjusted for updated means of bmi , ldl cholesterol , systolic blood pressure , and egfr instead of baselines of these variables . for avoidance of the potential bias due to severe diseases at baseline ,
additional analyses were carried out excluding the subjects who were diagnosed with lea during the first 2 years of follow - up .
statistical significance was considered to be p < 0.05 . all statistical analyses were performed with pasw for windows , version 20.0 ( ibm spss , chicago , il ) and sas for windows , version 9.3 ( sas institute , cary , nc ) .
the patient s characteristics , including age of diabetes diagnosis , sex , race / ethnicity , family income , smoking status , types of health insurance , body weight , height , bmi , blood pressure , total cholesterol , hdl cholesterol , ldl cholesterol , triglycerides , hba1c , estimated glomerular filtration rate ( egfr ) , history and incidence of peripheral arterial disease , ulcer , and foot deformity , and medication ( antihypertensive drugs , cholesterol - lowering drugs , and antidiabetes drugs ) within half a year after the diabetes diagnosis ( baseline ) and during follow - up after the diabetes diagnosis ( follow - up ) , were extracted from the computerized hospitalization records .
foot risk factors were identified using icd-9 codes based on existing literature ( 26,27 ) , which included peripheral arterial disease ( icd-9 codes 443.81 , 440.2 , 440.20 , 440.21 , 440.22 , 440.23 , 440.24 , 440.29 , 440.8 , 440.9 , 442.2 , 442.3 , 443.0 , 443.1 , 443.81 , 443.89 , 443.9 , 444.22 , 444.81 , 2507.x , and 785.4 ) , ulcer ( icd-9 codes 707.1x and 707.9 ) , and foot deformity ( icd-9 codes 94.0 , 713.5 , 727.1 , 735.0 , 735.2 , and 735.4735.9 ) .
the updated mean values of hba1c , ldl cholesterol , bmi , blood pressure , and egfr over time were measured first at baseline and second as an updated mean of annual measurement , calculated for each participant from baseline to each year of follow - up . for example , at 1 year the updated mean is the average of the baseline and 1-year values and at 3 years it is the average of baseline , 1-year , 2-year , and 3-year values . in case of an event during
follow - up , the period for estimating updated mean value was from baseline to the year before this event occurred ( 10,28 ) .
the average number of hba1c measurements during the follow - up period was 7.4 times .
follow - up information was obtained from the lsuhls inpatient and outpatient database by using the unique number assigned to every patient who visits the lsuhcsd hospitals .
the diagnosis of lea was the primary end point of interest of the study and was defined according to the icd-9 ( codes 84.1084.17 ) . since 1997 ,
diagnoses of lea were made by the treating physicians based on a clinical assessment and examinations as considered relevant by the clinician in charge of treatments .
follow - up of each cohort member continued until the date of the diagnosis of lea , the date of the last visit if the subject stopped use of lsuhcsd hospitals , death , or 31 may 2012 .
the association between hba1c and the risk of lea was analyzed by using cox proportional hazards models .
hba1c was evaluated in the following two ways : 1 ) as six categories ( hba1c < 6.0% [ 42 mmol / mol ] [ reference group ] , 6.06.9% [ 4252 mmol / mol ] , 7.07.9% [ 5363 mmol / mol ] , 8.08.9% [ 6474 mmol / mol ] , 9.09.9% [ 7585 mmol / mol ] , and 10.0% [ 86 mmol / mol ] ) and
different levels of hba1c were included in the models as dummy variables , and the significance of the trend over different categories of hba1c was tested in the same models by giving an ordinal numerical value for each dummy variable .
all analyses were adjusted for age and sex and further for smoking , income , types of insurance , bmi , systolic blood pressure , ldl cholesterol , egfr , peripheral arterial disease , ulcer , and foot deformity at baseline and during follow - up , use of antihypertensive drugs , use of diabetes medications , and use of cholesterol - lowering agents . when we analyzed the association between updated mean of hba1c and lea risk , we adjusted for updated means of bmi , ldl cholesterol , systolic blood pressure , and egfr instead of baselines of these variables . for avoidance of the potential bias due to severe diseases at baseline ,
additional analyses were carried out excluding the subjects who were diagnosed with lea during the first 2 years of follow - up .
all statistical analyses were performed with pasw for windows , version 20.0 ( ibm spss , chicago , il ) and sas for windows , version 9.3 ( sas institute , cary , nc ) .
general characteristics of the study population are presented by race in table 1 . during a mean follow - up period of 6.83 years
a significantly increased risk of lea was observed among both african american and white patients with increasing baseline hba1c ( table 2 ) .
after further adjustment for other confounding factors ( smoking , income , type of insurance , bmi , systolic blood pressure , ldl cholesterol , egfr , peripheral arterial disease , ulcer , and foot deformity at baseline and during follow - up and use of antihypertensive drugs , diabetes medications , and cholesterol - lowering agents ) , this graded association remained significant among white ( ptrend < 0.001 ) and african american ( ptrend < 0.001 ) patients with diabetes ( table 2 ) .
each 1% increase in baseline hba1c was associated with a 13% ( 95% ci 1.081.17 ) increased risk of lea in african americans and a 15% ( 95% ci 1.091.21 ) increased risk of lea in whites .
the risk of lea associated with hba1c was higher in white than african american patients with diabetes (  = 17.8 , df = 1 , p for interaction < 0.005 )
. baseline characteristics of african american and white patients with diabetes hazard ratio ( hr ) ( 95% ci ) of lea according to different levels of hba1c at baseline and during follow - up among african american and white patients with diabetes there was a significant interaction between sex and hba1c on lea risk ( table 3 ) .
when stratified by sex , the graded association of hba1c at baseline with lea risk was present and more significant in female patients with diabetes than male ( p for interaction < 0.001 ) . when we stratified by age , smoking status , family income , blood pressure , ldl cholesterol , and bmi , the graded positive association of baseline hba1c with lea risk did not change ( table 3 )
. moreover , the graded positive association of hba1c with lea risk was also confirmed among patients with diabetes using glucose - lowering agents or not ( all p trend<0.01 ) ( table 3 ) .
hazard ratio ( hr ) ( 95% ci ) of lea according to different levels of hba1c at baseline among various subpopulations when we did an additional analysis by using an updated mean of hba1c during follow - up , we found almost the same graded positive associations between baseline hba1c levels and updated mean levels of hba1c and lea risk among both african american and white patients with diabetes ( tables 2 and 4 ) .
the mean of hba1c decreased from 8.0% ( 64 mmol / mol ) to 7.7% ( 61 mmol / mol ) for african americans and from 7.3% ( 56 mmol / mol ) to 7.2% ( 55 mmol / mol ) for whites , but the graded positive association between hba1c and lea did not change ( supplementary table 1 )
. hazard ratio ( hr ) ( 95% ci ) of lea according to different levels of hba1c during follow - up among various subpopulations after exclusion of the subjects who were diagnosed with lea during the first 2 years of follow - up ( n = 208 ) , the multivariable - adjusted hrs of lea associated with different levels of hba1c did not change ( data not shown ) .
our study found a graded positive association between hba1c at baseline and during follow - up and the risk of lea among both african american and white patients with diabetes .
this graded positive association was more significant in white than african american patients with diabetes .
lea ranked first when participants rated their decrease in quality of life in the uk prospective diabetes study ( ukpds ) compared with other complications including blindness in one eye , stroke , heart failure , etc .
health care providers encourage and strive to achieve good glycemic control for patients with diabetes ; however , there are limited data on the specific effect of glycemic control on lea risk among patients with diabetes .
one meta - analysis of prospective studies demonstrated that there is a substantial increase in risk of lea associated with hyperglycemia in individuals with diabetes ( 30 ) ; however , small sample sizes ( 1,0443,642 participants ) , short follow - up ( 714 years ) , and few lea cases ( 44118 cases ) in each study limit the statistical power for subgroup analyses .
there are limited clinical trial data on the specific effect of glycemic control on lea . in the prospective pioglitazone clinical trial in macrovascular events ( proactive ) study
( 18 ) , there were 28 amputations among 2,605 participants in the pioglitazone group and 26 of 2,633 in the placebo group , and the event rate was lower in ukpds than in proactive ( 15,17 ) .
thus , it is quite difficult for a previous single prospective study or clinical trial to provide conclusive evidence about glucose lowering and lea risk ( 10,11,1518 ) .
there is an urgent necessity to provide robust data to confirm the associations between glycemia control and lea risk in the population with diabetes . in the current study , during a mean follow - up of 6.8 years , 578 lea incident cases among 35,368 participants with diabetes were identified .
we found a graded positive association by various hba1c intervals of clinical relevance or by using hba1c as a continuous variable at baseline and during follow - up with lea risk among both african american and white patients with diabetes .
in addition , we found that this graded positive association was present in patients with diabetes with and without glucose - lowering agent treatment and in patients with diabetes with different age , sex , smoking status , family income , blood pressure levels , ldl cholesterol , and bmi groups .
potential explanations for the increased risk of lea associated with hyperglycemia are likely to be mediated by number of mechanisms , which include but are not limited to peripheral sensory neuropathy , peripheral vascular disease , and soft - tissue sepsis .
first , the importance of hyperglycemia in the development of peripheral neuropathy is well documented ( 31 ) .
second , hyperglycemia contributes greatly to peripheral vessel disease in patients with diabetes ( 33 ) . finally , infection is present in the majority of foot ulcers , and hyperglycemia probably impairs host defense against infection . in the european study group on diabetes and the lower extremity ( eurodiale ) study ( 34 ) ,
peripheral arterial disease was diagnosed in 49% of the subjects and infection in 58% among patients with diabetic foot ulcers .
patients with peripheral neuropathy often fail to notice minor trauma resulting in ulceration , infection , and nonhealing diabetic foot ulcers to the ultimate lea .
improved glycemic control can potentially modify the risk of sensory neuropathy ( 35 ) and possibly the progression of peripheral arterial disease ( 36 ) .
there are several strengths in our study , including the large sample size , high proportion of african americans , long follow - up time , and use of administrative databases to avoid differential recall bias .
we have used both baseline hba1c levels and updated mean values of hba1c during follow - up in the analyses , which can avoid potential bias from a single baseline measurement .
in addition , participants in this study used the same public health care system , which minimizes the influence from the accessibility of health care , particularly when comparing african americans and whites .
one limitation of our study is that our analysis was not performed on a representative sample of the population , which limits the generalizability of the results ; however , lsuhcsd hospitals are public hospitals and cover > 1.6 million patients , most of whom are low - income persons in louisiana .
the results of the current study will have wide applicability for the population with low income and without health insurance in the u.s .
second , the validity of lea diagnoses in our study has not been confirmed by specialists . however , the method using hospital discharge registers to diagnose lea has been widely used in american and european cohort studies , such as the kaiser permanente medical care program ( 37 ) and the u.k . survey ( 38 ) .
the validity of the diagnoses of lea by using hospital discharge registers in these cohort studies is available ( agreement 9799% ) ( 37,38 ) .
third , even though our analyses adjusted for an extensive set of confounding factors , residual confounding due to the measurement error in the assessment of confounding factors and unmeasured factors such as physical activity , education , and dietary factors can not be excluded . in summary , our study demonstrates that there is a graded association between hba1c at baseline and during follow - up and the risk of lea among both african american and white patients with diabetes . in the absence of conclusive evidence from randomized intervention trials ,
our study provides further epidemiological support for glucose lowering as a strategy to reduce amputation in patients with diabetes .
 objectivediabetes confers a very high risk of lower - extremity amputation ( lea ) ; however , few studies have assessed whether blood glucose control can reduce lea risk among patients with diabetes , especially in practice settings where low - income patients predominate.research design and methodswe performed a prospective cohort study ( 20002009 ) on patients with diabetes that included 19,808 african americans and 15,560 whites . 
 the cohort was followed though 31 may 2012 . 
 cox proportional hazards regression models were used to estimate the association of hba1c with lea risk.resultsduring a mean follow - up of 6.83 years , 578 lea incident cases were identified . 
 the multivariable - adjusted hazard ratios of lea associated with different levels of hba1c at baseline ( < 6.0% [ reference group ] , 6.06.9 , 7.07.9 , 8.08.9 , 9.09.9 , and 10.0% ) were 1.00 , 1.73 ( 95% ci 1.072.80 ) , 1.65 ( 0.992.77 ) , 1.96 ( 1.143.36 ) , 3.02 ( 1.815.04 ) , and 3.30 ( 2.105.20 ) ( p trend < 0.001 ) for african american patients with diabetes and 1.00 , 1.16 ( 0.662.02 ) , 2.28 ( 1.353.85 ) , 2.38 ( 1.364.18 ) , 2.99 ( 1.715.22 ) , and 3.25 ( 1.985.33 ) ( p trend < 0.001 ) for white patients with diabetes , respectively . 
 the graded positive association of hba1c during follow - up with lea risk was observed among both african american and white patients with diabetes ( all p trend < 0.001 ) . 
 with stratification by sex , age , smoking status , blood pressure , ldl cholesterol , bmi , use of glucose - lowering agents , and income , this graded association of hba1c with lea was still present.conclusionsthe current study conducted in a low - income population suggests a graded association between hba1c and the risk of lea among both african american and white patients with type 2 diabetes . 
RESEARCH DESIGN AND METHODS
Baseline and follow-up measurements
Prospective follow-up
Statistical analyses
RESULTS
CONCLUSIONS
Supplementary Material