Whole blood clotting time: Current practices among Thailand National External Quality Assessment Scheme for blood coagulation member laboratories

INTRODUCTION

The Thai National Guidelines for Hemostatic Laboratory Testing were established in 2018. The guidelines recommend that the 20-min whole blood clotting time (20WBCT) method be used to diagnose/monitor snake bites. The aim of this study was to survey members of the Thailand National External Quality Assessment Scheme (NEQAS) for Blood Coagulation to investigate the use of 20WBCT testing compared between the 2021 post-guideline and 2007 pre-guideline periods.

METHODS

In July 2021, questionnaires were sent from the Faculty of Medicine Siriraj Hospital, Mahidol University to 521 Thailand NEQAS for Blood Coagulation member laboratories to survey their WBCT practices. Current WBCT practices were compared with pre-guideline WBCT practices, and chi-square test (x2) was used to test for differences between groups.

RESULTS

Ninety-seven (18.6%) of 521 surveys were returned. Seventy-one laboratories (73.2%) reported knowing about 20WBCT from the Thai national guidelines. The reported average frequency of overall WBCT testing in 2021 was 12.4 times/month. The proportion of laboratories that reported using the 20WBCT test increased from 2.0% in 2007 to 46.4% in 2021 (p < 0.001), and the indications for performing WBCT were virtually unchanged from 2007 to 2021. The proportion of laboratories that reported having problems with WBCT testing decreased from 32.7% in 2007 to 16.5% in 2021.

CONCLUSION

Despite our findings that almost three-quarters of respondent laboratories reported knowing about 20WBCT testing from the WBCT guidelines, and that WBCT-specific problems decreased significantly from 2007 to 2021, more work and training is needed to improve WBCT guideline dissemination, understanding, and adherence in Thailand.

Performance of the 20-minute whole blood clotting test in detecting venom induced consumption coagulopathy from Russell's viper (Daboia russelii) bites

The 20-minute whole blood clotting test (WBCT20) is used as a bedside diagnostic test for coagulopathic snake envenoming. We aimed to assess the performance of the WBCT20 in diagnosis of venom induced consumption coagulopathy (VICC) in Russell's viper envenoming. Adult patients admitted with suspected snake bites were recruited from two hospitals. WBCT20 and prothrombin time (PT) test were performed on admission. WBCT20 was done by trained clinical research assistants using 1 ml whole blood in a 5 ml borosilicate glass tube with a 10 mm internal diameter. The PT was measured by a semi-automated coagulation system and international normalised ratio (INR) calculated. VICC was defined as present if the INR was >1.4. The diagnostic utility of WBCT20 was determined by calculating the sensitivity and specificity of the WBCT20 on admission for detecting VICC. There were 987 snake bites where both WBCT20 and PT were done on admission samples. This included 79 patients (8 %) with VICC. The WBCT20 was positive in 65/79 patients with VICC (sensitivity 82 %; 95 % confidence interval [CI]: 72-90 %) and was falsely positive in 13/908 with no coagulopathy. The WBCT20 was negative in 895/908 snake bites with no coagulopathy (specificity: 98 % 95 % CI: 97-99 %) and was falsely negative in 14/79 with VICC. Using trained clinical staff, the WBCT20 test had a relatively good sensitivity for the detection of VICC, but still missed almost one fifth of cases where antivenom was potentially indicated.

Heparin monitoring during cardiac surgery. Part 1: validation of whole-blood heparin concentration and activated clotting time

There is limited published data on the agreement between techniques for monitoring heparin levels. The aim of this study was to validate the Hepcon/HMS, with particular focus on the agreement with laboratory anti-Xa assay. The performances of two ACT instruments - Hemochron and HemoTec - were also evaluated, including an assessment for interchangeability. Blood samples from 42 adult cardiopulmonary bypass (CPB) patients were analysed for activated clotting time (ACT), whole-blood heparin concentration (Hepcon/HMS) and anti-factor Xa (anti-Xa) plasma heparin concentration. Agreement between measures was determined using the method of Bland and Altman. Simple analysis of agreement between the Hepcon and anti-Xa heparin revealed the Hepcon has a mean bias of -0.46 U/mL, with the limits of agreement ±1.12 U/mL. The comparison between ACT instruments indicated a mean difference of -96 seconds for the HemoTec, with limits of ±265 seconds. The Hepcon/HMS instrument displayed satisfactory agreement with anti-Xa plasma heparin concentration, as the expected variation would not be expected to cause problems in the clinical setting. Agreement between the two measurements of ACT may be satisfactory, provided each is assigned a different target value.

Heparin monitoring during cardiac surgery. Part 2: calculating the overestimation of heparin by the activated clotting time

Activated clotting time (ACT) values were converted to heparin concentration, enabling an assessment of the accuracy of the ACT and a quantification of the prolongation imposed by bypass. Blood samples were obtained from 42 adult cardiopulmonary bypass (CPB) patients before and during bypass surgery. Samples were analysed for ACT (HemoTec ACT) and anti-factor Xa (anti-Xa) plasma heparin concentration. The mean heparin concentration calculated before bypass was an accurate reflection of plasma heparin; however, calculated values rose to around 170% of anti-Xa values upon connection to bypass. By adjusting for this rise, for 95% of cases the calculated heparin concentration would vary between 0.60 and 1.65 times anti-Xa values. Without accounting for artificial prolongation or individual sensitivities, the ACT may give values between 0.8 and 3.0 times that indicated by the anti-Xa assay. When both individual heparin sensitivities and the effects of bypass are considered, the ACT may provide a more suitable indication of heparin levels; however, typical use may overestimate heparin up to threefold.

Comparison of ACT point-of-care measurements: repeatability and agreement

Background: Accurate control of heparin anticoagulation is necessary during all stages of cardiopulmonary bypass (CPB). The activated clotting time, first described by Hattersley in 1966, is mostly used for determination of anticoagulation. Either celite or kaolin are used as activators. An ACT value of 480 sec is proposed to be the safe minimum level for anticoagulation during CPB. This study was designed to determine if the activated coagulation time (ACT) values of each analyser separately are repeatable, and to determine whether there exists a significant difference in ACT values measured by three different analysers: the GEM PCL (Instrumentation Laboratory), the Hemochron 801 (International Techni-dyne Corporation) and the ACT II Automated Coagulation Timer (Medtronic).

Methods: All patients underwent cardiovascular surgical procedures requiring heparinisation (200 - 300 IU/kg). Blood samples for the measurement of the ACT were taken from all patients before and after heparinisation, during CPB, and after protamine administration. All samples were measured in duplicate with the three different analysers. To compare the activated clotting time data, the method described by Bland and Altman was used. The Pearson correlation coefficient was used to determine whether the differences were related to the average ACTs. p-Values < 0.05 were considered statistically significant.

Results: The results showed that the three tested ACT analysers met the requirements of repeatability. The mean differences and standard deviations of the ACT values measured with the GEM PCL, the Hemochron 801, and the ACT II analyser were, respectively, -8.789 ± 37.61, -19.779±68.82, and -6.239±39.21, with p-values=0.177, 0.081 and 0.384, respectively. The Pearson correlation coefficients were too low (-0.012, -0.221 and -0.241, respectively) to show any correlation between the differences and the means. The ACT values measured with the Hemochron 801 were not significantly different from the ACT values measured with the ACT II analyser: ΔACT=-34.09 ± 146.68, with p=0.132. However, the GEM PCL did not agree with the Hemochron 801: ΔACT=-80.29 ± 143.06, with p=0.001, or the ACT II analyser: ΔACT=-119.139 ± 138.51, with p<0.001. A rather strong correlation was evident between the differences and the means measured with the GEM PCL compared with the Hemochron 801 (r=0.68) and the ACT II analyser (r=0.76).

Conclusions: All analysers used celite or kaolin as activator. However, it was evident that the ACT measurements depended also on the analyser that had been chosen. A precaution that ACT values could not always be interpreted in the same way seems to be necessary.

Has the new USP assay for heparin affected dosage for patients undergoing cardiopulmonary bypass?

In October 2009, the U.S. Pharmacopoeia (USP) changed the monograph for heparin to bring USP units in line with international units for heparin. The result was a 10% decrease in potency as measured by in vitro laboratory tests. This decrease led to questions regarding dosing guidelines. There existed a need for an in vivo study to determine the practical changes that may need to be implemented in regard to heparin administration for cardiopulmonary bypass in the clinical setting. A retrospective study was conducted to determine the heparin dose administered and the corresponding effect on patients undergoing coronary artery bypass grafting surgery using cardiopulmonary bypass. The study compared the heparin dose requirements and activated clotting time (ACT) results using the heparin before and after the USP changes. An analysis of the data was performed to determine the increased heparin dose required to achieve the same effect as before the USP change. This new heparin dosing protocol was instituted at Concord Hospital, Concord, NH. A prospective study was then preformed to verify the effects of the dosing change. In the new heparin group, the postheparin ACT fell by 9.1% (p = .028) and the patients achieving an ACT > 479 seconds fell by 12.8% as compared with the old heparin group. After adjustment of the loading dose calculation for heparin, the prospective study demonstrated the postheparin ACT (p = .684) and the percentage of patients achieving an ACT > 479 seconds (p = 1.000) to be similar to the values obtained before the USP change. An increase of the loading dose of approximately 12% is needed to achieve the patient effects seen before the UPS change.

Clotting time by free oscillation rheometry and visual inspection and a viscoelastic description of the clotting phenomenon

An automated procedure for determination of clotting time in whole blood was validated by direct comparison with the reference method, visual clotting time determination. The procedure was based on a 10 Hz free oscillation rheometer (FOR) of our design, the ReoRox 4. Recalcified citrated blood samples (n = 30), clotting in the range 4 to 20 min, were used in the validation. Every 30 s of the analysis, as the change in stiffness (deltaG*) of the sample was monitored by FOR, the sample cup was shortly removed from the FOR and its contents inspected for first signs of clotting, i.e. visual clotting time determination. Various FOR clotting criteria were attempted. Best correlation to visual clotting time was found when deltaG* reached 0.01 Pa, which yielded linear regression slope, intercept and r2 of 0.98, 0.09 min and 0.98, respectively. For comparison, six plasma samples were analyzed in the same way and gave almost the same results. The accuracy of the FOR determinations was checked by also analyzing, in parallel, portions of the sample with a conventional oscillation rheometer, a Bohlin VOR. The rationale is given for preferring deltaG* over G* as a FOR monitoring function in coagulation tests and for including median filtration of the primary FOR data. An extension of the FOR theory to include deltaG* and evidence in support of inhomogeneous blood clotting are also given.

A functional clotting assay to monitor the hirudin dosage

Hirudin, a direct thrombin inhibitor, has potential advantages over indirect thrombin inhibitors and is increasingly used in clinical settings. There are, however, large variations in individual responses to this drug and no recognized clinical laboratory tests used to monitor its anticoagulant effects. We evaluated the use of the thromboelastograph, a common clinical coagulation instrument, to monitor the effects of hirudin in vitro. We developed a novel, whole blood clotting assay that utilizes the tissue factor stimulating properties of mercuric ion to measure the anticoagulant potential of therapeutic doses of hirudin. At doses equivalent to those found in the therapeutic range, the thromboelastograph was capable of showing significant changes when compared with control and different concentrations of hirudin (P < 0.05). A linear relationship was observed between increasing concentrations of recombinant hirudin and clotting times. In conclusion, the use of this test system warrants further investigation for monitoring hirudin.

Plastic containers and the whole-blood clotting test: glass remains the best option

This is the first study to identify normal whole-blood clotting times in various plastic containers and to identify the effect of the addition of various concentrations of Pseudechis australis (Mulga snake) venom on the clotting time in glass and plastic. Polycarbonate was identified as a potential alternative to glass as a testing container owing to a whole-blood clotting time within acceptable limits for a bedside test (mean 29.5 min) and equivalent performance to glass in the presence of P. australis venom. Other plastic containers (such as polypropylene and polyethylene) were found to be unsuitable owing to very prolonged clotting times (>60 min) or impaired performance in the presence of venom. Overall, owing to the variation between the performance of different plastics and the difficulty in differentiating between them, plastic containers cannot be recommended as an alternative to glass when performing the whole-blood clotting test for envenomed patients.

Monitoring of activated coagulation time in carotid endarterectomy

BACKGROUND

The objective of the present study was to evaluate the efficacy of monitoring activated coagulation time (ACT) during carotid endarterectomy (CEA) in reducing surgical risks and complications.

METHODS

A total of 175 consecutive patients who had CEA between July 2002 and January 2004 were studied. Activated coagulation time was monitored during the procedure in all patients. The results were compared with the data reported in the literature, and with those obtained in 2 previous series, totaling 1924 patients treated at the same service before the use of ACT.

RESULTS

Only 4 of the 175 patients had cerebral ischemia, with 3 of them almost completely recovering during hospitalization. Significant morbidity was 0.6% and mortality was 0.6%. No statistically significant difference in the incidence of cerebral ischemia or death was observed between symptomatic and asymptomatic patients. In the 2 previous series used for comparison, operated by the same author, we found 0.7% and 0.8% of significant morbidity and 1.4% and 2.6% of mortality, respectively. Most series in the literature have shown a higher significant morbidity than the present one, mainly in symptomatic patients. The incidence of hematoma in the present series was 5.7%, only 3 (1.7%) of them being significant. No increase in the frequency of hematomas was observed in cases where heparin was not reversed or in those using a shunt. In the 2 other previous series, the incidence of hematomas was 1.5% and 3.6%.

CONCLUSIONS

Activated coagulation time monitoring during CEA was effective in evaluating the level of heparinization of patients during surgery and the immediate postoperative period. The comparison of the present series with the literature and with the previous series of the same service, before the use of ACT, permits also to conclude that the control of the level of heparinization seems to reduce the risk of perioperative and immediate postoperative ischemia. In addition, ACT monitoring also seems to be effective in diminishing the risk of postoperative cervical hematoma.

Measurement of the activated clotting time during cardiopulmonary bypass: differences between Hemotec ACT and Hemochron Jr apparatus

BACKGROUND

Measurement of the activated clotting time (ACT) represents a standard method for coagulatory assessments. The test employs specific agents to trigger the coagulation process. The present study aimed to compare kaolin (Hemotec) versus a combination of silica, kaolin and phospholipid (Hemochron Jr) ACTs.

METHODS

Hemotec and Hemochron Jr ACT monitors were compared by simultaneous measurement of paired arterial blood samples (n = 114) with respect to precision and bias during clinical conditions of cardiopulmonary bypass (CPB). The influence of haemodilution on the ACT was tested in an ex-vivo model.

RESULTS

The precision of Hemotec and Hemochron Jr ACT measurements attained 21 +/- 2.6 s versus 27.0 +/- 2.6 s (p = 0.126) during CPB and 2.5 +/- 2.2 s versus 9.4 +/- 6.9 s (p = 0.000) after protamine administration, respectively. The Hemochron Jr monitor was associated with a bias of -102 +/- 13.7 s compared to the Hemotec ACT monitor (p = 0.000) during CPB and -6.9 +/- 2.9 s after protamine (p = 0.025). Linear regression analysis of ACT readings between monitors reached r = 0.526 (p = 0.000). Hemochron Jr ACT values correlated with the erythrocyte volume fraction r = 0.379 (p = 0.000). Ex-vivo data indicated that the Hemotec ACT monitor was associated with relatively higher ACT readings after haemodilution.

CONCLUSION

The ACT is not a standardized measure. Test results are strongly associated with the specific compounds used to initiate the coagulation process.