Significantly different coagulation factor activities underlying the variability of 'normal' activated partial thromboplastin time.
ABSTRACT The activated partial thromboplastin time (aPTT) is a widely used coagulation screening test in routine laboratories. The aPTT level in the control population varies and is reflected by the reference interval. However, there have been no studies to investigate the coagulation status determining the variability of the aPTT. The aim of this study was to investigate the coagulation factor activities underlying the variability of aPTT in the population. The study participants were reference individuals with prothrombin time and aPTT within reference intervals. The aPTT was determined using STA-PTT Automate (Diagnostica Stago, Asnieres, France; local reference interval, 29.1-41.9 s). Those with aPTT within the marginal ranges of reference interval were selected for factor assays. We defined the lower marginal group as the lowest 10 percentile of reference interval (29.1-30.9 s) and the upper marginal group as the highest 10 percentile (38.0-41.9 s). Activities of factor II, V, VIII, IX, X, XI, and XII were determined in both groups. The lower marginal and upper marginal groups consisted of 220 and 209 individuals, respectively. All coagulation factors were significantly higher in the lower marginal than in the upper marginal group (P = 0.0127 for factor II and P < 0.0001 for the others). Multiple logistic regression analyses revealed factor XII and VIII were two strongest contributors determining the aPTT level, whereas factor XI was not significantly different between the groups (P = 0.095). This study firstly demonstrated significantly different coagulation factor activities underlying the variability of aPTT in reference individuals. The results suggested the possibility of disease association or phenotypic contribution of variable coagulation activities in the population.
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ABSTRACT: The activated partial thromboplastin time (aPTT) is a routine coagulation test that reflects the activities of multiple coagulation proteins. Given the known genetic elements underlying the different coagulation factor activities, a low intraindividual variability is expected in aPTT values, but has not been demonstrated in a large population. In this regard, we evaluated the intraindividual variability of aPTT by analyzing serial aPTTs from a large population. The study population consisted of control individuals who had three or more consecutive aPTT values at at least 6-month intervals at a single institution. The coefficient of variation of serial aPTT values was determined in each control individual, and the mean value of the coefficient of variations in the control population was calculated. The aPTT values from a total of 10 487 individuals [mean age 57 years (range 21-93 years); male-to-female ratio 1 : 0.9] were included. The mean value of the coefficient of variation of aPTTs in those individuals was 3.75%, which indicates a very low intraindividual variability. This is the first study to demonstrate a low intraindividual variability of aPTT in a large population. The result supports the previous notion that aPTT is a genetically determined parameter and has potential clinical implications.Blood coagulation & fibrinolysis: an international journal in haemostasis and thrombosis 10/2013; 24(7):746-8. · 1.25 Impact Factor