REGULAR ARTICLE Usefulness of high-concentration calcium chloride solution for correction of activated partial thromboplastin time (APTT) in patients with high-hematocrit value Masaaki Kanahara a , Hisashi Kai b, ⁎ , Takashi Okamura c , Toyofumi Wada d , Kenji Suda e , Tsutomu Imaizumi b , Kimitaka Sagawa a a Department of Laboratory Medicine, Kurume University Hospital, Kurume, Japan b Division of Cardio-vascular Medicine, Department of Medicine and Cardiovascular Research Institute, Kurume University School of Medicine, Kurume, Japan c Division of Hematology, Department of Medicine, Kurume University School of Medicine, Kurume, Japan d Department of Medical Informatics, Kurume University School of Medicine, Kurume, Japan e Department of Pediatrics, Kurume University School of Medicine, Kurume, Japan Received 20 April 2007; received in revised form 25 July 2007; accepted 15 August 2007 Available online 1 October 2007 Abstract Introduction: Pseudoprolongation of activated partial thromboplastin time (APTT) is a serious problem in anticoagulation therapy for patients with high hematocrit, such as cyanotic congenital heart diseases. APTT pseudoprolongation occurs when APTT assay is performed using routinely used vacuum sampling tubes containing citrate. Because the plasma fraction is small in high-hematocrit blood, the prescribed volume of citrate would be excessive for APTT assay, resulting in prolongation of clotting or APTT pseudoprolongation. CLSI — The Clinical and Laboratory Standards Institute (formerly NCCLS) method is the established method to correct the pseudoprolonga- tion. However, the CLSI method needs repeated blood drawings and time-consuming, complicate procedures. Thus, alternative simple method is desired. Method: We examined whether APTT pseudoprolongation would be prevented by the increase in free calcium ion concentration by using high-concentration calcium chloride solution for the assay. Blood samples were obtained from 15 patients with high hematocrit (65 ± 6%) who had cyanotic congenital heart disease. KEYWORDS APTT; Pseudohigh APTT values; CLSI method; Calcium chloride solution intl.elsevierhealth.com/journals/thre Abbreviations: APTT , Activated Partial Thromboplastin Time; CLSI, The Clinical and Laboratory Standards Institute. ⁎ Corresponding author. Tel.: +81 942 31 7562; fax: +81 942 33 6509. E-mail address: naikai@med.kurume-u.ac.jp (H. Kai). 0049-3848/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.thromres.2007.08.004 Thrombosis Research (2008) 121, 781–785