Establishing the co-efficient of variation, pre-analytical variables and normal ranges for coagulation factors VII and XI

Abstract

Having realised that local normal reference ranges (NRR) for coagulation factors (CF) VII and XI had not yet been established; the aim of this research project was to establish Maltese NRR for CF VII and XI. This stems from the fact that NRR should be established for the local population whenever possible, as reference ranges might be influenced by the biological variability between subjects from different populations (Makris & Kitchen, 2009). Blood samples from consenting adults (n=59) age ranging from 18-60, presenting with no active or pre-existing medical conditions and not receiving any anti-coagulant therapy, were recruited. 50 subjects were used for the establishment of NRR for CF’s VII and XI, whilst simultaneously investigating the effect of gender on FVII and FXI values. Furthermore, 9 subjects from the control group were utilised for testing the effects of preanalytical variables relating to: specimen acquisition, transport, processing and storage on the stated assays. The prothrombin time (PT) and activated partial thromboplastin time (APTT) were measured for each individual prior to measuring factor activity levels. Factor VII was measured by a PT-based clotting assay, whilst Factor XI was measured by an APTTbased clotting assay. PT levels did not differ between the genders (p>0.05). However, APTT levels were significantly different between the two genders (p<0.05), with males expressing slightly higher values than females. Factor VII and XI activity levels did not differ with gender (p>0.05). In regards to the pre-analytical variables, PT values were only affected by the length of processing time upon specimen collection. APTT values were affected only by the number of centrifugation cycles (single versus double). FVII activity levels seemed to be only affected by the method of transportation used (pneumatic tube versus hand delivery). To the contrary, FXI activity levels were affected by the number of centrifugation cycles and the duration of storage time prior to processing. Intra-assay and inter-assay coefficient of variation values levels for PT, APTT, FVII and FXI assays were very minimal, indicating high reproducibility of results.