the relation between chronic subclinical low - grade inflammation and insulin resistance ( ir ) has long been known [ 1 , 2 ] .
ir is the major contributor and mediating factor in the development of type 2 dm ( t2 dm ) along with concomitant hypertension ( ht ) and cardiovascular disease ( cvd ) [ 3 , 4 ] .
the relationship between the development of dm and some markers of inflammation such as c - reactive protein ( crp ) , il-6 , fibrinogen , and pai-1 has been described previously .
serum concentration of crp increases in both impaired glucose tolerance ( igt ) and overt t2 dm [ 3 , 510 ] . on the other hand
, some studies reported that elevation of crp is an indicator of development of t2 dm . compared with the conventional ogtt ( 2-hpg ) as recommended by who as gold standard , fasting plasma glucose ( fpg ) and hba1c are more convenient , simpler , and cost - effective diagnostic methods that are currently in use for the diagnosis of t2 dm [ 5 , 1217 ] .
however , each test recognizes people with different metabolic features and groups who may be diagnosed by different tests but do not overlap substantially . while high postchallenge plasma glucose is a strong predictor of cvd , fasting glucose is not an independent predictor of cvd .
to the best of our knowledge , there is no previous report specifically comparing the role of hs - crp in people with newly diagnosed dm with the criteria based on the 2-hpg , fpg , and hba1c .
therefore , the aim of this study was to identify the optimal cut - off points of hs - crp in new - onset ( previously undiagnosed ) people with dm diagnosed based on the current 2-hpg , fpg , and hba1c diagnostic criteria . in this study
, hs - crp results obtained from a nationally representative population - based survey are being reported .
data derived from  the turkish epidemiology survey of diabetes , hypertension , obesity and endocrine diseases ( turdep - ii ) ,  a population - based study , which was included randomly assigned 26,499 adult people from 270 urban and 270 rural centers .
the field survey was performed between january and june 2010 , with a participation rate of 85% .
the study was approved by the local ethical board ( istanbul medical faculty ethical committee , 16.4.2008/699 ) .
people with known dm or other systemic diseases who had hs - crp levels of 10  mg / l ( 95.2  nmol / l ) or above were excluded from this study due to a possible infection .
all biochemical tests including glucose , insulin , and lipid profile were measured in fasting blood samples using roche diagnostics modular autoanalyzer system ( roche diagnostics , germany ) in the central biochemistry laboratory of istanbul medical faculty .
concentration of hs - crp was analyzed by immunoturbidimetric assay ( roche / hitachi 912 , modular p analyzers : acn 210 ; crpl3 tina - quant c - reactive protein gen .
3 ) and hba1c by turbidimetric inhibition immunoassay ; both the system and the laboratory have been regularly certified ( roche diagnostics tq hba1c gen .
3 ; ngsp certificate of traceability ; september 2010 - 2011 ) . a detailed medical history of each participant was obtained , and measurements of anthropometry ( height , weight , waist , and hip circumference ) and systolic and diastolic blood pressure ( sbp , dbp ) were done .
body mass index ( bmi ) , homa - ir (= fasting glucose  fasting insulin/405 ) , and non - hdl - cholesterol (= total cholesterol  hdl - cholesterol ) were calculated accordingly .
glomerular filtration rate ( egfr ) was estimated using  chronic kidney disease epidemiology collaboration  ckd - epi equation .
risk factors for dm were evaluated using chi - square test ; mean values by sex were compared using nonparametric mann - whitney u test .
homogeneity of variance and normal distribution of variables were tested by kolmogorov - smirnov test .
pearson correlation coefficients ( r values ) were calculated to assess the association between hs - crp and other laboratory parameters .
mean levels of hs - crp in each of the new dm groups were further compared using univariate analysis after being adjusted for age , bmi , smoking and alcohol drinking , and sbp and dbp .
an optimum cut - off point of hs - crp was estimated using the receiver operating characteristic ( roc ) curve and area under the curve ( auc ) with 95% cis was calculated for each of the new dm groups that were diagnosed with fpg , 126  mg / dl ( 7.0 
mmol / l ) , 2-hpg : 200  mg / dl ( 11.1  mmol / l ) , or hba1c : 6.5% ( 48  mmol / mol ) [ 13 , 17 ] .
optimum cut - off points of hs - crp were defined for men and women , separately . as the raw data
not normally distributed when log transformed , we obtained a square root transformation ( sqrt ) of the hs - crp levels , and after defining the cut - off points we recalculated the squares .
data were analyzed using spss for windows ( version 21.0 ; spss / ibm , chicago , il ) .
demographic characteristics and laboratory findings of women and men in turdep - ii study are presented in table 1 . in brief , men were significantly older and had higher mean weight , waist circumference , sbp , dbp , triglycerides ( tg ) , hdl - cholesterol , and non - hdl - cholesterol values than women .
women had significantly higher bmi , hip circumference , heart rate , fpg , hba1c , 1-hpg , 2-hpg , hdl - cholesterol , and egfr values than men .
median ( interquartile range , iqr ) concentration of hs - crp in women was significantly higher than in men ( women , 1.85 [ 3.09 ] 
total serum cholesterol , fasting serum insulin , and homa - ir values did not differ between men and women ( table 1 ) .
there was a positive correlation between hs - crp levels and age , bmi , waist , hip , sbp , dbp , pulse , fpg , hba1c , 1-hpg , 2-hpg , tg , non - hdl - cholesterol , and homa - ir ; and there was a negative correlation with hdl - cholesterol and egfr .
when we repeated the analysis after controlling for ht , age , sex , smoking and alcohol use , bmi , and waist circumference , the positive correlations between hs - crp levels and hba1c , 1-hpg , 2-hpg , tg , non - hdl - cholesterol , egfr , and homa - ir and the negative correlation with hdl - cholesterol and creatinine remained significant ( table 2 ) . among people with new dm ,
the highest hs - crp level was in the group detected by hba1c criterion ( hs - crp median [ iqr ] ; hba1c : 3.45 [ 3.82 ]  mg / dl , 32.9 [ 36.4 ]  nmol / l ; 2-hpg : 2.7 [ 3.14 ]  mg / dl , 25.4 [ 29.9 ]  nmol / l ; and fpg : 2.4 [ 3.0 ]  mg / dl , 22.4 [ 28.5 ]  nmol / l , data not shown ) .
high sensitive crp level was significantly higher in women than men with newly diagnosed dm groups based on 2-hpg , fpg , and hba1c criteria . among the newly diagnosed dm groups , the median [ iqr ] level of hs - crp was highest in those detected with hba1c in both genders ( hba1c - group : women : 4.0 [ 4.1 ]  mg / dl , 38.4 [ 39.1 ]  nmol / l ; men : 2.7 [ 3.1 ]  mg / dl , 25.9 [ 29.1 ]  nmol / l ; fpg group : women : 3.3 [ 4.1 ]  mg / dl , 31.1 [ 39.3 ]  nmol / l ; men : 2.4 [ 3.0 ]  mg / dl , 22.4 [ 28.5 ]  nmol / l ; and 2-hpg group : women : 2.8 [ 3.3 ]  mg / dl , 26.5 [ 31.3 ]  nmol / l ; men : 2.4 [ 2.8 ]  mg / dl , 23.3 [ 26.9 ] 
sex differences in hs - crp did not change after the data adjusted with respect to age , bmi , waist circumference , and ht ; the mean hs - crp was highest in newly diagnosed patients based on hba1c criterion in both sexes .
again , the average hs - crp levels of women were higher than men ( table 3 ) . in women with newly diagnosed dm based on fpg ,
mean hs - crp level was comparable to those diagnosed with 2-hpg but lower than the group diagnosed with hba1c ( p = 0.000032 ) .
women with newly detected dm based on 2-hpg had also lower mean hs - crp than those detected with hba1c ( p < 0.000001 ) .
in contrast , men with newly detected dm based on fpg criterion had lower mean hs - crp than those diagnosed with 2-hpg ( p = 0.017 ) and hba1c ( p = 0.003 ) but mean hs - crp levels were comparable in 2-hpg and hba1c based new dm groups ( table 3 ) .
the specificity and sensitivity of the optimal cut - off points for hs - crp to detect dm in women were for the fpg group , 60% and 57% for 2.5  mg / l ( 23.6 
nmol / l ) , 2-hpg group , 60% and 54% for 2.1  mg / l ( 19.7  nmol / l ) , and 65% and 64% for hba1c group , 2.9  mg / l ( 27.5  nmol / l ) . in men the corresponding specificity and sensitivity values were as follows : fpg group : 60% and 57% for 1.8  mg / l ( 16.9  nmol / l ) ; 2-hpg group : 60% and 57% for 1.8  mg /
l ( 16.9  nmol / l ) ; and hba1c group : 65% and 60% for 2.0  mg / l ( 19.0  nmol / l ) ( roc curves figure 1 and table 4 ) . the largest auc value for hs - crp to detect dm was found in women and men when using hba1c ( women : 0.700 ; men : 0.656 ) . the positive and negative predictive values ( ppv and npv ) corresponding to the above - mentioned cut - points of hs - crp in women
were calculated as 58% and 59% for fpg , 57% and 58% for 2-hpg , and 64% and 65% for hba1c and in men were 58% and 59% for fpg , 58% and 59% for 2-hpg , and 61% and 61% for hba1c .
our current population - based study identified 1,727 people with newly diagnosed dm based on at least one of the three methods .
however , the people identified to have dm were substantially different for each of the three methods .
in other words , the concordance rate for dm among the different methods of glycaemia testing was low .
characteristics of the people with dm and their risk factors may vary by the method used for the detection of dm .
several studies have suggested that inflammation is associated with ir that takes part in the pathogenesis of t2 dm and atherosclerotic disease [ 14 , 6 ] .
environmental factors such as infections , overnutrition , and lack of physical activity are believed to contribute serum crp levels although the mechanism is not properly understood . on the other hand ,
hyperglycaemia per se may induce inflammation and this may enhance the development of dm [ 21 , 22 ] .
demonstrated that people who developed dm ( detected by an ogtt ) had higher baseline serum crp levels than those who did not develop dm .
there was a linear increasing trend in the incidence of dm as the baseline crp quartile increased .
in pizarra prospective study , people with baseline hs - crp 3  mg / l ( 28.6  nmol / l ) developed dm . in our previous report , we demonstrated a linear increasing trend for hs - crp levels from normal glucose tolerance through impaired fasting glucose ( ifg ) , igt , and new dm . a recent meta - analysis including 18 prospective studies demonstrated that high baseline crp levels associated with future t2 dm diagnosed based on fpg and/or 2-hpg criteria .
all these findings support the chronic low - grade inflammation hypothesis in the development of dm . in our study
, we found a positive correlation between hs - crp levels and all glycaemia and ir parameters .
however , after adjustment for age , sex , smoking , bmi , waist , and ht , positive correlations were maintained with hba1c , 1-hpg and 2-hpg , fasting insulin , and homa - ir but not with fpg . in their later report festa et al . stated that postchallenge glucose but not fpg was strongly correlated with baseline crp .
other studies have also shown an association between crp and dm , which remained significant after adjusting for bmi or other covariates .
our findings and others suggested that adiposity is not sufficient to explain the relationship between high levels of inflammatory markers and increased dm risk .
the predictive value of hs - crp did not seem to be fully independent of obesity in several [ 3 , 23 , 24 , 27 , 28 ] but not all studies [ 7 , 9 , 10 , 22 ] .
our results showed that among people with new dm the highest hs - crp levels were obtained in those identified with the hba1c criterion .
hba1c elevation at diagnosis is an indication of overt dm , but in a more advanced stage compared with new - onset dm detected with the fpg or 2-hpg criteria .
as we did show a positive correlation between hs - crp and hba1c , it has been reported that people with dm with poorer glycaemic control had higher crp levels .
some commonly used medications like aspirin and statin may synergistically reduce serum crp concentrations [ 29 , 30 ] . in the present study ,
we excluded people with known systemic disease and those who self - reported regularly using such medications ; however , we may not ascertain all people using aspirin and/or statin .
aronson et al . reported that crp levels among middle - aged people were higher in those with dm and ifg when compared with the healthy subjects .
similar to our findings showing women had higher hs - crp levels than men regardless of having dm or not , the adopt investigators have reported that hs - crp levels in women were higher than in men in both with and without the metabolic syndrome ( ms ) .
they reported a positive correlation between hs - crp and hba1c , bmi and homa - ir and the number of ms components in people with new dm .
in women 's health study , the incidence of dm was four times higher in women with hs - crp levels in the upper quartile in comparison with those with hs - crp levels in the lowest quartile .
wu and coworkers reported that high levels of hs - crp were correlated with high levels of hba1c and fpg in men and with only fpg in women .
other studies reported strong correlations between hs - crp and fasting insulin , homa - ir , and fpg [ 21 , 34 ] and an inverse correlation with crp and hdl - cholesterol [ 3 , 21 ] ; all were confirmed in our study .
we estimated the optimal cut - off hs - crp and auc - crp with 95% cis for dm for each of the three diagnostic methods separately . to the best of our knowledge ,
this is the first study aiming at determining hs - crp cut - off points indicating new dm compared with each of the three methods assessing hyperglycaemia .
the highest cut - off point for hs - crp was obtained with hba1c based new dm detection compared to fpg and 2-hpg methods .
in fact we previously showed that new dm group detected with hba1c has a more advanced metabolic disorder ( higher bmi , waist , blood pressure , non - hdl - cholesterol , triglycerides , and insulin but lower hdl - cholesterol ) than other new dm groups detected with fpg or 2-hpg . den engelsen et al . attempted to find a cut - off point for hs - crp that would indicate the presence of the ms . if hs - crp cut - off point was set at 3  mg / l ( 28.6  nmol / l ) , the sensitivity and specificity were 72% and 37% ; at this point ppv and npv were 42% and 67% . in another study performed in a japanese population , a cut - off point of hs - crp of 0.65  mg / l ( 6.2  nmol / l ) for fpg 100  mg / dl ( 5.6  mmol / l ) or higher was capable of defining the ms with a 100% sensitivity and 77% specificity in women and with a 65% sensitivity and 63% specificity in men . in our study the optimum cut - point of hs - crp of 2.5  mg /
l ( 23.6  nmol / l ) in women and 1.8  mg / l ( 16.9  nmol / l ) in men for fpg 126  mg / dl ( 7.0  mmol / l ) or higher was capable of defining the new dm with a 60% sensitivity and 57% specificity in both genders . the optimum cut - point for hba1c 6.5% and
over was 2.9  mg / l ( 27.5  nmol / l ) in women with a 65% sensitivity and 64% specificity and 2.0  mg / l ( 19.0  nmol / l ) in men with a 60% sensitivity and 62% specificity , and the largest auc value for hs - crp to detect new dm was found in women and men when using hba1c ( women : 0.700 ; men : 0.656 ) .
these high cut - off points of crp may be related with the more advanced diabetic state as compared to fpg or 2-hpg based detected cases .
one of the greatest strengths of the present study is its national representative sampling with a large sample size and wide age range .
in addition , this is the first study where all three currently proposed methods ( 2-hpg , fpg , and hba1c ) were used to define dm and each of them was compared with the inflammation marker , hs - crp .
the major limitations are the cross - sectional design and somewhat higher participation rate in women , controlled in the data analyses . in brief ,
an hs - crp level 1.8  mg / l ( 16.9  nmol / l ) generally detects more than half of the people with new dm .
external validation of our findings needs to be carried out in additional studies in other populations with reasonably large sample size before these findings can be generalized .
our results revealed that hs - crp may not further strengthen the diagnosis of new - onset dm .
however , the highest hs - crp among people with new dm was found in those identified with the hba1c criterion .
this suggests that high hba1c may recognize new dm cases at a more advanced stage than fpg or 2-hpg in an ogtt .
. it would be important to find out if people with newly detected dm with high hs - crp require a more intensive therapy than those with low hs - crp .
 fasting plasma glucose ( fpg ) and hemoglobin a1c ( hba1c ) have been used to diagnose new - onset diabetes mellitus ( dm ) in order to simplify the diagnostic tests compared with the 2-hour oral glucose tolerance test ( ogtt ; 2-hpg ) . 
 we aimed to identify optimal cut - off points of high sensitive c - reactive protein ( hs - crp ) in new - onset dm people based on fpg , 2-hpg , or hba1c methods . 
 data derived from recent population - based survey in turkey ( turdep - ii ) . 
 the study included 26,499 adult people ( 63% women , response rate 85% ) . 
 the mean serum concentration of hs - crp in women was higher than in men ( p < 0.001 ) . 
 the people with new - onset dm based on hba1c had higher mean hs - crp level than fpg based and 2-hpg based dm cases . in hba1c , 2-hpg , and 
 fpg based new - onset dm people , cut - off levels of hs - crp in women were 2.9 , 2.1 , and 2.5  mg / l [ 27.5 , 19.7 , and 23.5  nmol / l ] and corresponding values in men were 2.0 , 1.8 , and 1.8  mg / l ( 19.0 , 16.9 , and 16.9  
 nmol / l ) , respectively ( sensitivity 6065% and specificity 5464% ) . 
 our results revealed that hs - crp may not further strengthen the diagnosis of new - onset dm . 
 nevertheless , the highest hs - crp level observed in new - onset dm people diagnosed with hba1c criterion supports the general assumption that this method might recognize people in more advanced diabetic stage compared with other diagnostic methods . 
1. Introduction
2. Material and Methods
3. Results
4. Discussion
5. Conclusions