Discard first tube for coagulation testing

Tracking the dynamics of thrombus formation in a blood vessel-on-chip with visible-light optical coherence tomography

Thrombus formation is a physiological response to damage in a blood vessel that relies on a complex interplay of platelets, coagulation factors, immune cells, and the vessel wall. The dynamics of thrombus formation are essential for a deeper understanding of many disease processes, like bleeding, wound healing, and thrombosis. However, monitoring thrombus formation is challenging due to the limited imaging options available to analyze flowing blood. In this work, we use a visible-light optical coherence tomography (vis-OCT) system to monitor the dynamic process of the formation of thrombi in a microfluidic blood vessel-on-chip (VoC) device. Inside the VoC, thrombi form in a channel lined with a monolayer of endothelial cells and perfused by human whole blood. We show that the correlation of the vis-OCT signal can be utilized as a marker for thrombus formation. By thresholding the correlation during thrombus formation, we track and quantify the growth of the thrombi over time. We validate our results with fluorescence microscopic imaging of fibrin and platelet markers at the end of the blood perfusion assay. In conclusion, we demonstrate that the correlation of the vis-OCT signal can be used to visualize both the spatial and temporal behavior of the thrombus formation in flowing human whole blood.

A comparison of coagulation test results from heparinized central venous catheter and venipuncture

: Blood sampling via heparin-locked central venous catheter, including coagulation tests, is possible in accordance with the Clinical & Laboratory Standards Institute guidelines. However, differences exist between the test values of samples obtained from central venous catheter and those obtained from peripheral veins, even the guidelines are followed. To compare the coagulation time between blood samples from the heparin-locked central venous catheter and peripheral veins. In total, 72 hospitalized patients using heparin-locked Hickman catheters were enrolled. Blood samples for coagulation testing were simultaneously obtained via the peripheral veins and heparin-locked Hickman catheters. For sampling from the catheters, 0.9% sodium chloride flushing was performed and 10 or 23 ml of blood was discarded prior to collecting the coagulation test samples. Correlation, Bland-Altman plot, covariate, and regression analysis were performed for data analyses. Despite following the guidelines, the activated partial thromboplastin time test values differed. In the 10 ml of blood discard group, a correlation coefficient of 0.378 and a mean bias of 6.46 s were determined, while and in the 23 ml blood discard group, a correlation coefficient of 0.80 and a mean bias of 2.518 s were determined. Therefore, the volume of blood discarded from the heparin-locked Hickman catheters may affect the activated partial thromboplastin time test values.

Increasing the sensitivity of the human microvesicle tissue factor activity assay

INTRODUCTION

The TF-FVIIa complex is the primary activator of coagulation. Elevated levels of microvesicle (MV) bearing tissue factor (TF)-dependent procoagulant activity are detectable in patients with an increased risk of thrombosis. Several methods have been described to measure MV TF activity but they are hampered by limited sensitivity and specificity. The aim of this work was to increase the sensitivity of the MV TF activity assay (called Chapel Hill assay).

MATERIAL AND METHODS

Improvements of the MV TF activity assay included i/ speed and time of centrifugation, ii/ use of a more potent inhibitory anti-TF antibody iii/ use of FVII and a fluorogenic substrate to increase specificity.

RESULTS

The specificity of the MV TF activity assay was demonstrated by the absence of activity on MV derived from a knock-out-TF cell line using an anti-human TF monoclonal antibody called SBTF-1, which shows a higher TF inhibitory effect than the anti-human TF monoclonal antibody called HTF-1. Experiments using blood from healthy individuals, stimulated or not by LPS, or plasma spiked with 3 different levels of MV, demonstrated that the new assay was more sensitive and this allowed detection of MV TF activity in platelet free plasma (PFP) samples from healthy individuals. However, the assay was limited by an inter-assay variability, mainly due to the centrifugation step.

CONCLUSIONS

We have improved the sensitivity of the MV TF activity assay without losing specificity. This new assay could be used to evaluate levels of TF-positive MV as a potential biomarker of thrombotic risk in patients.

Preanalytical investigations of phlebotomy: methodological aspects, pitfalls and recommendations

Phlebotomy is often addressed as a crucial process in the pre-analytical phase, in which a large part of laboratory errors take place, but to date there is not yet a consolidated methodological paradigm. Seeking literature, we found 36 suitable investigations issued between 1996 and 2016 (April) dealing with the investigation of pre-analytical factors related to phlebotomy. We found that the largest part of studies had a cohort of healthy volunteers (22/36) or outpatients (11/36), with the former group showing a significantly smaller median sample size (N = 20, IQR: 17.5-30 and N = 88, IQR: 54.5-220.5 respectively, P < 0.001). Moreover, the largest part investigated one pre-analytical factor (26/36) and regarded more than one laboratory test (29/36), and authors preferably used paired Student’s t-test (17/36) or Wilcoxon’s test (11/36), but calibration (i.e. sample size calculation for a detectable effect) was addressed only in one manuscript. The Bland-Altman plot was often the preferred method used to estimate bias (12/36), as well as the Passing-Bablok regression for agreement (8/36). However, often papers did assess neither bias (12/36) nor agreement (24/36). Clinical significance of bias was preferably assessed comparing to a database value (16/36), and it resulted uncorrelated with the size of the effect produced by the factor (P = 0.142). However, the median effect size (ES) resulted significantly larger if the associated factor was clinically significant instead of non-significant (ES = 1.140, IQR: 0.815-1.700 and ES = 0.349, IQR: 0.228-0.531 respectively, P < 0.001). On these evidences, we discussed some recommendations for improving methodological consistency, delivering reliable results, as well as ensuring accessibility to practical evidences.

Routine coagulation testing: do we need a discard tube?

When coagulation tests are performed, the recommended guideline is that a discard tube be used and the coagulation testing should be done only on the second tube. This guideline is however inconsistently enforced and most laboratories follow a single tube draw for routine coagulation testing. Few studies have however, challenged this guideline and have shown that comparable results can be obtained in both tubes when a two tube draw is used. This prospective study was done over a 3 months period in the hematology laboratory under the Clinical Hematology unit of a tertiary care teaching institution in North India. Fifty-six paired specimens were drawn from healthy volunteers following the prescribed "two tube draw" method. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were performed within 1 h of sample collection on a fully automated photo-optical coagulation instrument (Ceveron-Alpha). Paired results for PT and APTT were compared using Bland-Altman plots for method comparison. There was good correlation between the PT, INR and APTT of the first and second tubes with bias of 0.09, -0.05 and 0.3 respectively). Bland-Altman plots showed acceptable agreement between the two values with 95 % confidence interval ranging from -0.62 to 0.79 for PT, -0.05 to 0.06 for INR and -3.9 to 4.6 for APTT. Our study has shown no significant difference between PT and APTT values for the first and second tubes. Hence the use of a discard tube is not required.