the incidence of autoimmune diseases ( aids ) such as systemic lupus erythematosus ( sle ) , rheumatoid arthritis , and primary biliary cirrhosis ( pbc ) has been increasing in china . until now ,
the antinuclear antibody ( ana ) test , wherein antibodies are detected by indirect immunofluorescence assay on hep-2 cells , is commonly used as an initial screening method .
the presence of ana is nonspecific and can be associated with many nonautoimmune factors , such as carcinoma , infection , pharmaceuticals , and environmental factors . as a result ,
an ana positive frequency in healthy individuals > 20% has been reported . on the other hand
, ana may exist several years before an aid can be diagnosed , with higher titer of ana being correlated closely with a higher risk of the onset of aids during adolescence and adulthood .
the epidemiologic characteristics of aid in different countries and districts varies . to our knowledge ,
information about the ana prevalence and the susceptibility or potential of aids in the general population of china is lacking .
we aimed to evaluate the ana prevalence in a wide range of the general chinese population ( aged 288 years ) .
to assess the ana positive rate among the general population of china , we conducted a cross - sectional study .
twenty thousand nine hundred seventy sera were taken from the physical examination center in baoding , hebei , china , from july 2011 to september 2013 ( figure 1 ) .
the sample size and male to female ratio conform to the standard of the sixth national census of china in 20102011 ( http://www.stats.gov.cn/tjsj/pcsj/rkpc/6rp/indexch.htm ) .
a total of 6800 children ( including 3300 girls and 3200 boys ) aged from 2 to 18 years were recruited from 3 public kindergartens , 5 middle schools , and 2 high schools .
the other participants consisted of 14,170 individuals ( 7220 women and 6950 men ) obtained by random sampling .
the study complied with the world medical association declaration of helsinki and was approved by the ethics committee of the first center hospital of bao ding .
to assess the ana positive rate among the general population of china , we conducted a cross - sectional study .
twenty thousand nine hundred seventy sera were taken from the physical examination center in baoding , hebei , china , from july 2011 to september 2013 ( figure 1 ) .
the sample size and male to female ratio conform to the standard of the sixth national census of china in 20102011 ( http://www.stats.gov.cn/tjsj/pcsj/rkpc/6rp/indexch.htm ) .
a total of 6800 children ( including 3300 girls and 3200 boys ) aged from 2 to 18 years were recruited from 3 public kindergartens , 5 middle schools , and 2 high schools .
the other participants consisted of 14,170 individuals ( 7220 women and 6950 men ) obtained by random sampling .
the study complied with the world medical association declaration of helsinki and was approved by the ethics committee of the first center hospital of bao ding .
sera were tested by indirect fluorescence on hep-2 cells according to the manufacturer s instructions ( euroimmun ag , lubeck , germany ) . titer 1:320 was considered to be positive . as a result , 243 positive samples were further tested by line immunoassay ( lia ) ( euroimmun ag ) for 15 specific autoantibodies ( ie , anti - nrnp , anti - sm , anti - ssa , anti - ro52 , anti - ssb , anti - jo-1 , anti - scl-70 , anti - cnepb , anti - dsdna , anti - his , anti - pcna , anti - nuk , anti - rib , anti - m2 , and anti - pmscl-70 ) .
euroblotmaster ( euroimmun ag ) and eurolinescan ( euroimmun ag ) were used to complete the operation and for test result interpretation , respectively .
spss for windows version 17.0 ( ibm - spss , inc , armonk , new york ) was used for statistical calculations .
spss for windows version 17.0 ( ibm - spss , inc , armonk , new york ) was used for statistical calculations .
the age and sex distribution of 20,970 participants are summarized in table i. the ages ranged from 2 to 88 years , with mean age 32 ( 19.7 ) years for both sexes .
the prevalence of ana in male and female participants by age groups are shown in table i. the overall prevalence of ana was 5.92% and correlated positively with age .
there were significant differences among each age group except age older than 80 years , as shown in table i ( p < 0.01 ) . in the female group ,
there are 2 sharp peaks in ana positivity at the 20-year and 40-year age groups . in 1243 ana - positive sera tested by lia ,
44.2% were positive for at least 1 of 15 specific ana antibodies . in terms of the effect of age and sex on ana positivity , there were significant differences among the 3 groups ( ie , 20 years , 2149 years , and 50 years ;  = 275.04 ; p < 0.01 ) , and between male and female (  = 236.47 ; p < 0.01 ) , as shown in table i and table ii , respectively . the autoantibodies with the top-3 positive frequency were anti - ro-52 ( 19% ) , anti - m2 ( 17.8% ) , and anti - ssa ( 14.3% ) ; whereas anti - scl-70 , anti - jo-1 , and anti - sm were the less frequently detected antibodies among the autoantibodies detected ( table iii ) .
this is the first research into the prevalence of ana in the general chinese population .
satoh et al hold that the ana prevalence in the us population of individuals aged 12 years and older is 13.8% , and based on national health and nutrition examination survey 1999 - 2004 data , more than 32 million people in the united states are positive for ana .
other studies indicate that japanese show a 9.5% prevalence at a 1:100 cutoff level dilution , whereas for indians it is 12.3% .
anti - ro-52/ssa was the most detected antibody in both of those studies . in the present and another relevant study ,
based on that comparison among different nations , we hold the opinion that ana positive frequency in adults differs by geography .
sex and age had been assumed to be the factors that influenced ana positivity . in our study , ana prevalence correlated positively with age on the whole , with higher prevalence present in the 20- to 30-year and 40- to 50-year groups .
the latter peak is in line with the single peak at age 40 to 49 years described in a us population that was characterized by the physiologic stage of puberty and menopause , implying that estrogen may play an important role . as such
, some similarities of genetic deposition and hormone factors may have an influence on disease manifestations . between the sexes ,
our results indicate that the female to male ratio in ana positive cohorts is almost 4:1 , except in the 80 years group .
our study also showed that ana positivity in girls ( 8.2% ) was higher than in boys ( 2.5% ) .
this indicated that females have a higher ana titer than males even at a relatively immature stage . because ana - iif is a primary screening test for adolescent sle ,
hayashi et al reported that it is important to emphasize the ana titer as a prognostic marker in certain aids , and a 1:160 or 1:320 dilution titer is recommended .
although ana may be influenced by nonimmune factors , several articles show that the positive frequency is no more than 5% at a dilution titer of 1:160 in the general population . in our study , at the cutoff value of 1:320 titer , we found a similar result to previous studies in that older people were prone to higher frequency of ana positivity than younger people ( figure 2 ) .
consistent with the findings in a japanese population , we found anti - ro52/ssa was the most prevalent autoantibody in the general population .
ro-52/ssa is a useful serologic marker for sle and sjogren syndrome , myositis , systemic sclerosis , and pbc .
anti - ro / ssa and antichromatin had the highest predictive value for sle diagnosis .
the prevalence of patients with asymptomatic pbc in an asian population derived from previous studies seemed to be larger than that inferred from our study .
coincident to the data from japanese residents , our results showed that anti - scl-70 , anti - jo-1 , anti - nuk , and anti - sm were the least - detected antibodies .
it is a pilot study on a large - scale population without comprehensive consideration of other factors such as occupation , genetic deposition , and biochemical factors .
ana positive frequency is high in the general chinese population and differs in different sex and age groups .
the authors have indicated that they have no conflicts of interest regarding the content of this article .
 backgroundthe incidence of autoimmune diseases such as systemic lupus erythematosus , rheumatoid arthritis , and primary biliary cirrhosis has increased significantly in china . 
 information about the susceptibility or potential of autoimmune diseases in the general population is lacking.objectiveto explore the prevalence of antinuclear antibody ( ana ) and its specificities in the general population in china.methodstwenty thousand nine hundred seventy sera samples were taken from the physical examination center in baoding , china . 
 indirect immunofluorescence and line immunoassays were used to detect ana and its specificities , respectively.resultssamples from females had a higher prevalence of ana than samples from males ( 2 = 278.55 ; p < 0.01 ) . for both sexes , 
 the prevalence of ana positively correlated with age and there were significant differences among different age groups at 10-year intervals , except the 80 years group ( p < 0.05 ) . 
 one thousand two hundred forty - three ana - positive samples were further analyzed with line immunoassays . 
 there was a significant difference among age groups and between sex groups in terms of the specific autoantibodies ( p < 0.01 ) . 
 the autoantibodies with the top-3 positive frequencies were anti - ro-52 , anti - m2 , and anti-ssa.conclusionsthere was a high prevalence of ana positivity in the general chinese population that seemed to be influenced by sex and age and correlated with specific autoantibodies . 