en Clinical Biochemistry Clinical Biochemistry Original Research Original Research <p> <strong> Abstract </strong></p><p> <strong> Background: </strong>Recently, small dense low density lipoprotein (sdLDL) has been </p><p>  highlighted as a new risk factor for the coronary artery disease (CAD).Small dense </p><p>  LDLs are believed to be atherogenic since these particles are taken up more easily by </p><p>  arterial wall. They are readily oxidized and have reduced affinity for low density </p><p>  lipoprotein (LDL) receptor and increased affinity for arterial proteoglicans. LDL </p><p>  cholesterol is only a measure of the cholesterol level in the LDL whereas apolipoprotein </p><p>  B(apo B) is a measure of the cholesterol levels of all the atherogenic particles, including </p><p>  very low density lipoprotein, intermediate density, and low density lipoproteins. </p><p>  Therefore, it might be a better marker than other traditional lipids. The aim of </p><p>  the present study was to evaluate the association between serum small dense LDL, </p><p>  apolipoprotein B, apolipoprotein A1 (apo A1) and apoB/apoA1 ratio and the coronary </p><p>  stenosis. </p><p> <strong> Methods: </strong>86 patients with coronary stenosis , 35 patients without coronary stenosis </p><p>  identified by angiography who were referred to Rajaii Heart Center , and 30 </p><p>  healthy individuals were studied. SdLDL was measured by a direct homogenous </p><p>  LDL-C assay in the supernatant of serum which remained after heparin-magnesium </p><p>  precipitation. Serum apolipoprotein A1 and apolipoprotein B were measured by using </p><p>  immunoturbidimetric method. </p><p> <strong> Results: </strong>The results showed that the sdLDL levels were higher in patients with </p><p>  coronary stenosis than patients without coronary stenosis and healthy individuals </p><p>  (21.54±7.1, 16.88±4.4 and 15.45±5mg/dl, p=0.001, respectively). In addition the level </p><p>  of apoB (with stenosis: 113.71±21.8, without stenosis:100.88±18.7 and healthy: </p><p>  102.30±9.6, p=0.003) and apoB/apoA1 ratio (with stenosis:1.100±0.24, without </p><p>  stenosis :0.589±0.26 and healthy:0.751±0.16, p=0.001) were significantly higher in </p><p>  patients with coronary stenosis. SdLDL levels were positively correlated with the </p><p>  level of apoB(r=0.589), apoB/apoA1 ratio(r=0.416), triglyceride(r=0.494), LDL-C </p><p>  (r=0.749), Total cholesterol(r=0.354) and were inversely correlated with the level of </p><p>  HDL-C (r = -0.586)(p<0.01). </p><p> <strong> Conclusion: </strong>The elevated levels of small dense LDL, apoB and apoB/apoA1 ratio </p><p>  were associated with coronary artery stenosis. </p><p>  </p> small dense LDL, apolipoprotein, coronary artery disease 8 13 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-1-31&slc_lang=en&sid=1 Ladan Hosseini Gohari lhgh@iums.ac.ir 20031947532846001744 20031947532846001744 Yes Faculty of Allied Medicine and Cellular and Molecular Research Center of Iran Romina Karimzadeh Ghassab 20031947532846001745 20031947532846001745 No Iran University of Medical Sciences. Tehran, Iran. Mohsen Firoozray 20031947532846001746 20031947532846001746 No Faculty of Medicine, Iran University of Medical Sciences. Abbas Zavarehee 20031947532846001747 20031947532846001747 No Shahid Rajaii Heart Center, Tehran. Hossein Ali Basiri 20031947532846001748 20031947532846001748 No Shahid Rajaii Heart Center, Tehran, Iran.