Thromboplastin standards

Abstract

The Prothrombin Time (PT) test is used for monitoring of treatment with Vitamin K-antagonists (VKA). The result of the PT test should be expressed as the International Normalized Ratio (INR). Calculation of INR is based on the availability of International Standards (IS) for thromboplastin and a calibration model. Calibration of a new PT test system is performed with the appropriate IS and fresh plasma samples of healthy (normal) volunteers and patients treated with VKA. The calibration model is based on the assumption of a linear relationship between the log(PT)'s obtained with the new PT system and the reference IS for both normal and patients' samples. Patients' samples for calibration should be selected by rejecting samples beyond the 1.5-4.5 INR range. Outliers should be rejected defined as points with a perpendicular distance greater than three residual standard deviations from the line of relationship. Selection of patients' samples and rejection of outliers result in a reduction of the between-laboratory variation of calibration. In addition to monitoring of VKA, the PT is used for management of patients with chronic liver disease. Likewise, INR(liver) should be based on calibration with an IS using samples from patients with chronic liver disease.

Long-term stability of international standards for thromboplastin stored at -20°C, -70°C, and -150°C

“…The observed differences may be due to instability of the plasma samples at room temperature [11]. International Standards for thromboplastin have an established value for the International Sensitivity Index (ISI) [1][2][3]. The ISI values for RBT/05 and rTF/09 were established in 2005 and 2009, respectively.…”

“…The difference plot of the natural logarithms of prothrombin times indicated a significant correlation (P = 0.013). parameter used for calibration of secondary standards [1,8]. As no material is absolutely stable, it has to be verified whether the real value after some time of storage still corresponds to the assigned (i.e.…”

“…International Standards for thromboplastin are biological preparations containing Tissue Factor (TF) [1]. TF is an integral transmembrane protein functioning as a cofactor enhancing the proteolytic activity of coagulation factor VIIa towards factor X and factor IX in blood.…”

Management of Anticoagulation Around Cardiac Implantable Electronic Device Surgery

“…Moreover, heparin has antiplatelet effects that may last longer than the measurable effect of heparin and APTT [13]. Meanwhile, the evidence to maintain a therapeutic INR during the procedure is based on more consistent data of cohorts and randomized trials [14,15]. Performing surgery under anticoagulation can facilitate the detection of small bleedings during the procedure [16].…”

Calibration of combined thromboplastins with the International Standard for Thromboplastin, rabbit, plain

“…First, the ISI difference might be due to different blood collection tubes or other differences in pre-analytical conditions between the original calibration studies for OBT/79 and RBT/05 [3][4][5]. Second, a bias might have been introduced by multiple consecutive calibrations of the International Standards with asymmetric exclusion of samples [6,7]. Third, a physical or chemical change of at least one of these reference materials during long-term storage at low temperature cannot be excluded but is not very likely [8].…”