[Heparin-induced thrombocytopenia (HIT) adalah salah satu efek sampingpenggunaan heparin, yang dicurigai bila terdapat penurunan trombosit ≥50% padahari ke-5 sampai ke-10 pascaheparinisasi dan dapat disertai komplikasitromboemboli. Mekanisme HIT melibatkan pembentukan antibodi terhadapkompleks PF4-heparin (anti-PF4). Pemeriksaan diagnostik HIT terdiri dari ujifungsional dan immunoassay. Pemeriksaan immunoassay, yang mendeteksi anti-PF4 dengan metode ELISA memiliki sensitivitas tinggi dan paling seringdigunakan untuk deteksi HIT. Angka kejadian HIT sangat bervariasi karenabanyak faktor yang mempengaruhi. Tujuan penelitian ini adalah untukmengetahui proporsi kejadian HIT dan proporsi pasien yang memiliki anti-PF4pada pemberian terapi heparin di RSCM.Penelitian ini melibatkan 120 pasien rawat inap yang mendapat dripheparin atas indikasi profilaksis atau pengobatan, dengan dosis minimal 10.000U/24 jam. Pasien yang memenuhi kriteria masukan dan tolakan dilakukanpencatatan data usia, jenis kelamin, diagnosis klinis, riwayat pemakaian heparin 3bulan terakhir, dan dosis heparin yang dipakai. Pada hari ke-7 dan ke-10pascaheparinisasi (H7 dan H10) dilakukan pengambilan darah untuk pemeriksaanhitung trombosit dan anti-PF4. Diagnosis HIT didasarkan atas penurunan hitungtrombosit ≥50% pada H7 atau H10 yang disertai adanya antibodi anti-PF4. Hasiluji ketelitian within-run dan uji ketepatan pemeriksaan anti-PF4 mendapatkan CV7,73% dan penyimpangan (d) 2,5-17,4%. Pada 19 dari 120 subjek (15,8%)ditemukan anti-PF4, tetapi kejadian HIT tidak ditemukan. Berdasarkan klasifikasirisiko terjadinya HIT menurut American College of Chest Physician (ACCP),terdapat 46/120 subjek (38,3%) berisiko rendah, 65/120 subjek (54,2%) berisikotinggi, 8/120 subjek (6,7%) berisiko sangat tinggi, dan 1 orang tidak terklasifikasi.Uji statistik menunjukkan tidak ada hubungan antara temuan anti-PF4 denganpenurunan trombosit ≥50% (p=0,588). Hal ini diduga karena kurangnya jumlahsubjek penelitian yang diperlukan. Antibodi anti-PF4 lebih sering ditemukan padasubjek perempuan dan dengan riwayat heparinisasi. Proporsi ditemukannya anti-PF4 berturut-turut lebih banyak pada pasien pascabedah vaskular dan ortopedi,trombosis arteri dan vena, kemudian pasien medis yang mendapat profilaksisheparin. Tidak ada perbedaan bermakna proporsi anti-PF4 positif pada subjekdengan atau tanpa riwayat heparinisasi (p=0,293), perbedaan dosis heparin(p=0,141), dan populasi risiko HIT rendah, tinggi, dan sangat tinggi (p=0,662).Empat dari 19 subjek yang memiliki anti-PF4 positif mengalami penurunantrombosit 20-46% pada H7 dan H10., Heparin-induced thrombocytopenia (HIT) is an adverse effect of heparin,that suspected when platelet count fall ≥50% in 5 to 10 days following heparininitiation and may be accompanied with thromboembolic complications.Mechanism of HIT is mediated by the formation of PF4-heparin complexantibody. There are 2 kind of diagnostic test for HIT, functional assay andimmunoassay. Immunoassays, that detect anti-PF4 antibody using ELISA method,have high sensitivity and considered the most frequent assay for detecting HIT.The incidence of HIT varies due to many factors. The aim of this research is tofind the proportion of HIT events and also the proportion of anti-PF4-heparinantibody positive in patients with full-dose heparin in Cipto Mangunkusumohospital.One hundred and twenty participants, who were our hospital in-patientsgiven heparin infusion with minimal dose of 10.000U/24 h for profilactic ortreatment indication, participated in this research. Patients met the inclusion andexclusion criteria were noted for age, gender, clinical diagnosis, heparin exposurein the last 3 months, and heparin dose. On day 7 and 10 after heparin initiation,blood sample were collected for platelet count and anti-PF4 antibody assay.Diagnosis of HIT was based on platelet count fall ≥50% on day 7 or 10 afterheparin initiation accompanied with anti-PF4 antibody in the circulation. Withinrun precision and accuracy tests for anti-PF4 assay showed a CV of 7,73% anddeviations of -2,5 – 17%. Nineteen of 120 subjects (15,8%) had anti-PF4antibodies, but HIT was not found. Based on the risk classification of HIT fromAmerican College of Chest Physician (ACCP), 46 subjects (38,3%) categorized aslow risk to HIT, 65 (54,2%) high risk, 8 (6,7%) very high risk, and 1 asunclassified. Statistics showed there was no significant relationship between anti-PF4 antibodies in the circulation with platelet count fall of ≥50% (p=0,588). Thiswas probably due to inadequate sample size for this study. Anti-PF4 antibodieswere detected more frequent in females and subjects with past heparin exposure.The proportion of positive anti-PF4 antibodies were highest in postoperativevascular or orthopedic surgery patients, followed by arterial or venous thrombosispatients, then medical patients using profilactic dose of heparin. There were nosignificant difference of positive anti-PF4 antibodies in subjects with vs withoutpast heparin exposure (p=0,293), in subjects using 10.000U/24h vs >10.000U/24hheparin dose (p=0,141), and in subjects with low vs high vs very high risk of HIT(p=0,662). Four of 19 subjects having anti-PF4 antibodies had platelet count fall20-46% on day 7 and day 10.]