Background: Fetal and neonatal hemostatic systems are dynamic. Coagulation and inhibitors of coagulation factors are progressively synthesized by the fetus which begins after 34 weeks of pregnancy and at the initial hours after birth. The neonatal hemostatic system generally shifts towards hypercoagulability. During sepsis, this hypercoagulability is exacerbated by an imbalance of coagulation and inhibitors of coagulation factors including antithrombin III. This study aimed to determine differences of antithrombin III levels in neonatal sepsis positive blood cultures (proven sepsis) and negative blood cultures (unproven sepsis). Methods: The subjects of this study were 26 patients of neonatal sepsis, which consisted of 13 positive blood cultures and 13 negative blood cultures. Levels of antithrombin III were examined by chromogenic methods. Examination of blood cultures of grampositive bacteria using manual method and gram-negative bacteria Latar belakang: Sistem hemostatis janin dan neonatus bersifat dinamis. Koagulasi dan inhibitor faktor koagulasi secara progresif disintesis oleh janin yang dimulai sejak 34 minggu kehamilan dan jam-jam awal setelah dilahirkan. Sistem hemostatis neonatus umumnya bergeser ke arah hiperkoagulabititas. Selama sepsis, hiperkoagulabilitas ini diperburuk dengan adanya ketidakseimbangan koagulasi dan inhibitor faktor koagulasi termasuk antitrombin III. Tujuan penelitian ini untuk mengetahui perbedaan kadar antitrombin III pada sepsis neonatal kultur darah positif (proven sepsis) dan kultur darah negatif (unproven sepsis). Metode: Subyek penelitian ini adalah 26 pasien sepsis neonatal, yang terdiri dari 13 kultur darah positif dan 13 kultur darah negatif. Kadar antitrombin III diperiksa dengan metode kromogenik. Pemeriksaan kultur darah bakteri Gram positif dilakukan dengan metode manual dan bakteri Gram negatif dengan metode using semiautomatic method. Data analysis uses an independent t test. Results: Antithrombin III levels in neonatal sepsis patients positive blood culture (73,23 ± 21,62) didn't differ significantly compared to negative blood cultures (65,63 ± 20,81) with p = 0,370 (p> 0,05). The bacterial pattern that caused neonatal sepsis were Staphylococcus sp. (84,6%), CoNS (81,8%), Staphylococcus aureus (18,2%)}, Salmonella spp (7,7%) and Klebsiella pneumoniae ssp pneumoniae (7,7%). The sensitivity pattern of Staphylococci to cefoxitin to determine resistence, found 5 Methicillin-resistant Staphylococci (MRS) and 1 Meticillin-resistant Staphylococcus aureus (MRSA). Conclusion: There were no significant differences of antithrombin III levels in neonatal sepsis positive blood cultures and negative blood cultures. semiautomatik. Analisis data menggunakan uji-t independent. Hasil: Pola kuman penyebab sepsis neonatal adalah Staphylococcus sp. (84,6%), Coagulase-negative Staphylococci (CoNS) (81,8%), Staphylococcus aureus (18,2%)}, Salmonella spp (7,7%) dan Klebsiella pneumoniae ssp pneumoniae (7,7%). Pola sensitivitas bakteri Staphylococci terhadap Cefoxitin untuk melihat resisten...