Heparin monitoring: the confusion continues

Periovulatory anticoagulant therapy enhances embryo recovery rates in superovulated mares

Although protocols for superovulation have been described in horses, this technique has been discouraged due to the low embryo recovery rates in superovulated mares. The reason for these poor results is poorly understood, but the formation of a blood clot in the ovulation fossa following ovulations has been hypothesized. Therefore, this study aimed to assess the safety and effect of periovulatory anticoagulant therapy on embryo recovery of superovulated mares. In experiment 1, five mares were assigned to receive five anticoagulant treatments in a crossover design: intravenous injections of 150 (H1), 300 (H2), 400 (H3), 450 (H4), 600 (H5) IU/kg of unfractionated heparin (UFH, heparin sodium); and had blood samples sequentially collected for up to 48 h post-treatment to test Prothrombin (PT) and activated partial thromboplastin time (aPTT). In experiment 2, four mares were treated in a crossover design with intravenous injection of 450 IU/kg of UFH and 1 mg/kg of low molecular weight heparin (LMWH, enoxaparin) and had blood collected as previously for analysis of plasma anti-Xa activity. In experiment 3, eleven mares had four cycles randomly assigned to four groups. In the control group, mares did not receive any treatment. In contrast, in groups G1, G2, and G3, mares were superovulated with equine pituitary extract and treated 34 h after the induction of ovulation with a placebo (NaCl 0.9 %, G1), 450 IU/kg of UFH (G2), or 1 mg/kg of LMWH. Mares in all groups had ovulation induced with hCG plus histrelin acetate and were bred with fresh semen from one stallion. Embryo flushing was performed nine days post-ovulation. In experiment 1, only mares in groups H4 and H5 had increased aPTT and PT for up to 12 h, and in all groups, aPTT and PT values returned to baselines at 24 h post-treatment. In experiment 2, plasma anti-Xa activity was increased by both therapies for up to 12 h after treatment and was at baseline levels 24 h post-treatment. In experiment 3, periovulatory therapy with anticoagulants increased embryo recovery rates per cycle (G2, 250 %; G3, 260 %) compared to control-assigned cycles (60 %; P < 0.05), whereas G1-assigned cycles (160 %) had intermediate embryo recovery. In conclusion, periovulatory anticoagulant therapies may be an alternative to improve embryo recovery in superovulated mares.

Minimum protamine dose required to neutralize heparin in cardiac surgery: a single-centre, prospective, observational cohort study

PURPOSE

Excess protamine contributes to coagulopathy following cardiopulmonary bypass (CPB) and may increase blood loss and transfusion requirements. The primary aim of this study was to find the least amount of protamine necessary to neutralize residual heparin following CPB using the gold standard assays of anti-IIa and anti-Xa activity. Secondary objectives were to evaluate whether the post-CPB activated clotting time could be used as a surrogate marker for quantifying heparin neutralization.

METHODS

Twenty-eight consecutive patients undergoing elective cardiac surgery were enrolled. Protamine administration was standardized through an infusion pump at 25 mg·min-1. Blood samples were withdrawn prior to and following administration of 150, 200, 250, and 300 mg protamine and analyzed for activated clotting time and anti-IIa and -Xa activity.

RESULTS

Following a mean (standard deviation) cumulative heparin dose of 67,700 (19,400) units and a CPB duration of 113 (71) min, protamine requirements varied widely. Eight out of 25 (32%) patients showed complete neutralization of anti-IIa and -Xa activity at the first sampling point (150 mg protamine; protamine:heparin ratio, 0.3 [0.1]). A protamine:heparin ratio of 0.5 (0.2) was sufficient for heparin neutralization in > 90% of patients. After CPB, a low to mid-range activated clotting time correlated well with anti-IIa and -Xa activity.

CONCLUSIONS

The protamine:heparin ratio required to neutralize residual unfractionated heparin (UFH) following CPB is variable. A protamine:heparin ratio of 0.3 was sufficient to neutralize UFH in some patients, while a ratio of 0.5 is sufficient to neutralize both residual anti-IIa and -Xa activity in most patients. Larger studies are necessary to confirm these findings and evaluate their clinical implications.

STUDY REGISTRATION

ClinicalTrials.gov (NCT03787641); registered 26 December 2018.

Unfractionated heparin anticoagulation using estimated blood volume based dosing versus weight-based dosing in a Veteran population

OBJECTIVE

The purpose of this study is to compare estimated blood volume (EBV) versus weight-based (WB) dosing of unfractionated heparin in terms of safety and ability to achieve therapeutic antifactor-Xa (AF-Xa) levels.

METHODS

This was a retrospective, cohort study including 32 male veterans who received UFH. Primary outcome measures included time until therapeutic anticoagulation, number of adjustments needed to achieve therapeutic anticoagulation, median AF-Xa levels and the percentage of patients who were therapeutic after the first and second levels. Safety was determined as the incidence of major and minor bleeding.

RESULTS

EBV dosing may be associated with a decrease in the average time to therapeutic range (20.4 ± 16.7 hours with EBV vs. 26.8 ± 26 hours with WB; p = 0.404) and an increase in the percentage of patients achieving therapeutic anticoagulation after the first AF-Xa level (50% with EBV vs. 35.7% with WB; p = 0.611) although these results were not statistically significant. WB dosing required fewer adjustments (2.7 ± 2.9 with WB vs. 4 ± 2.6 with EBV; p = 0.192) with more patients within the therapeutic range after the second AF-Xa level (42.9% with WB vs. 33.3% with EBV; p = 0.897). There was one major and three minor bleeds in the WB dosing group versus one minor bleed for the EBV dosing cohort (p = 0.438 and p = 0.323, respectively).

CONCLUSION

EBV dosing achieved quick therapeutic anticoagulation with less bleeding compared to WB dosing in a veteran population. Due to the study's limitations, larger, randomized, comparative trials are needed to confirm our findings.

Antifactor Xa levels vs. activated partial thromboplastin time for monitoring unfractionated heparin. A pilot study

WHAT IS KNOWN AND OBJECTIVES

The two most common methods for monitoring unfractionated heparin (UFH) infusion are the activated partial thromboplastin time (aPTT) and the antifactor Xa heparin assay (anti-Xa). The purpose of this study is to compare the performance of an aPTT protocol vs. an anti-Xa protocol in adult patients as defined by the time to reach therapeutic range, the percentage of time the values were within the goal range and the number of times laboratory monitoring was conducted. We then analysed the discordance between paired values of anti-Xa and aPTT.

METHODS

This was a single-centre prospective cohort pilot study conducted from 1 September 2013 to 31 May 2014.

RESULTS

Eighty-five patients were treated with UFH infusion, aPTT monitoring (n = 48), anti-Xa monitoring (n = 37). The number of times aPTT and anti-Xa values were ordered was (median, IQR) 14 (2-34) vs 7 (2-76); P = 0·23. The time to reach therapeutic range in hours was (mean, SD) 22 (20) aPTT vs 15 (13) anti-Xa; P = 0·08. Therapeutic range (>50-100% of the time) was achieved in only 5 (10%) patients in the aPTT group vs. 21 (57%) in the anti-Xa group; P < 0·01. Supratherapeutic values (>50-100%) were observed in 38 (78%) patients in the aPTT group vs. 14 (38%) in the anti-Xa group; P < 0·01. The discordance between aPTT and anti-Xa was evaluated using 234 paired values from 37 patients. There was discordance between anti-Xa and aPTT values 57% of the time. Two patients had bleeding complications requiring blood transfusion or discontinuation of post-pilot protocol.

WHAT IS NEW AND CONCLUSION

Utilizing an anti-Xa protocol to monitor heparin infusion showed favourable results compared with utilizing an aPTT protocol by maintaining values within the therapeutic goal range. The most common discordant pattern in our study was a disproportionate prolongation of aPTT to anti-Xa values. Patients with discordant values presenting with high aPTT to normal anti-Xa values may have an increased risk of bleeding complications.

Monitoring of Unfractionated Heparin Using Activated Partial Thromboplastin Time

Background:

We frequently encounter high levels of activated partial thromboplastin time (aPTT) during heparin anticoagulation. The purpose of this study is, first, to investigate the rate of achieving and maintaining therapeutic aPTT in patients treated with heparin anticoagulation and second, to assess the adequacy the current nomogram.

Methods:

We included 197 patients who underwent anticoagulation with unfractionated heparin (UFH) according to the standard nomogram between September 2008 and May 2010. The primary endpoints were the rate of achieving a therapeutic range (TR) at the first sample, 24 hours, or 48 hours. We also compared heparin nomograms according to age (<70 years vs ≥70years).

Results:

Of the 197 patients, 131 had heparin loading. In the heparin loading group, there were 19.1% (n=25), 69.5% (n=91), and 90.1% (n=18) achieving TR at the first aPTT, 24 hours, and 48 hours, respectively. The therapeutic aPTT proportion was 39.2%, and the rate of peak level above 90 seconds was 93.1%. Peak levels of aPTT were higher in the older age group than in the younger age group (202.3 ± 124.2 versus 152.0 ± 78.9, p=0.007).

Conclusion:

Our results indicate a high rate of achieving therapeutic aPTT at 24hous and 48hours, but a low success rate for maintenance within the TR. Most patients had supratherapeutic aPTT of more than 90 seconds. Therefore, the TR of aPTT that matches heparin levels of 0.3 to 0.7 IU/mL measured by antifactor Xa assay should be determined. If not, we should consider adopting a new heparin dosing nomogram.

Antifactor Xa levels versus activated partial thromboplastin time for monitoring unfractionated heparin

Intravenous unfractionated heparin (UFH) remains an important therapeutic agent, particularly in the inpatient setting, for anticoagulation. Historically, the activated partial thromboplastin time (aPTT) has been the primary laboratory test used to monitor and adjust UFH. The aPTT test has evolved since the 1950s, and the historical goal range of 1.5-2.5 times the control aPTT, which first gained favor in the 1970s, has fallen out of favor due to a high degree of variability in aPTT readings from one laboratory to another, and even from one reagent to another. As a result, it is now recommended that the aPTT goal range be based on a corresponding heparin concentration of 0.2-0.4 unit/ml by protamine titration or 0.3-0.7 unit/ml by antifactor Xa assay. Given that several biologic factors can influence the aPTT independent of the effects of UFH, many institutions have transitioned to monitoring heparin with antifactor Xa levels, rather than the aPTT. Clinical data from the last 10-20 years have begun to show that a conversion from aPTT to antifactor Xa monitoring may offer a smoother dose-response curve, such that levels remain more stable, requiring fewer blood samples and dosage adjustments. Given the minimal increased acquisition cost of the antifactor Xa reagents, it can be argued that the antifactor Xa is a cost-effective method for monitoring UFH. In this review, we discuss the relative advantages and disadvantages of the aPTT, antifactor Xa, and protamine titration tests, and provide a clinical framework to guide practitioners who are seeking to optimize UFH monitoring within their own institutions.

Activated partial thromboplastin time versus antifactor Xa heparin assay in monitoring unfractionated heparin by continuous intravenous infusion

BACKGROUND

Unfractionated heparin (UFH) has been used clinically for 5 decades. Despite being a cornerstone of anticoagulation, UFH is limited by its unpredictable pharmacokinetic profile, which makes close laboratory monitoring necessary. The most common methods for monitoring UFH are the activated partial thromboplastin time (aPTT) and antifactor Xa heparin assay (anti-Xa HA), but both present challenges, and the optimal method to monitor UFH remains unclear.

OBJECTIVE

To compare the performance of the aPTT with the anti-Xa HA for efficiency and safety of monitoring intravenous UFH infusions.

METHODS

This was a single-center, retrospective, observational cohort study conducted in an 852-bed academic medical center.

RESULTS

One hundred patients receiving intravenous UFH for a variety of indications were enrolled in the study; 50 were assigned to each group. The mean (SD) time to achieve therapeutic anticoagulation was significantly less in the anti-Xa HA group compared with the aPTT group (28 [16] vs 48 [26] hours, p < 0.001). In addition, a greater percentage of anti-Xa HA patients compared to aPTT patients achieved therapeutic anticoagulation at 24 hours (OR 3.5; 95% CI 1.5 to 8.7) and 48 hours (OR 10.9; 95% CI 3.3 to 44.2). Patients in the anti-Xa HA group also had more test values within the therapeutic range (66% vs 42%, p < 0.0001). A significant difference was seen between the 2 groups in the number of aPTT or anti-Xa HA tests performed per 24 hours (p < 0.0001) and number of infusion rate changes per 24 hours (p < 0.01), both favoring the anti-Xa HA group.

CONCLUSIONS

Monitoring intravenous UFH infusions with the anti-Xa HA, compared to the aPTT, achieves therapeutic anticoagulation more rapidly, maintains the values within the goal range for a longer time, and requires fewer adjustments in dosage and repeated tests.

Achieving Target Antifactor Xa Activity with a Heparin Protocol Based on Sex, Age, Height, and Weight

STUDY OBJECTIVES

To develop and validate an improved unfractionated heparin (UFH) dosage protocol, using antifactor Xa levels as the outcome variable.

DESIGN

Prospective case series.

SETTING

A 625-bed, adults-only private, tertiary care teaching hospital.

PATIENTS

Three hundred seventy-two patients receiving UFH for eight different indications were in the protocol derivation group. One hundred ninety-seven patients were in the final validation group. Intervention. Variables that predicted successful UFH treatment were determined by analysis of variance and regression.

MEASUREMENTS AND MAIN RESULTS

Sex, age, height, weight, UFH dosage, and antifactor Xa levels were variables. A regression model using sex, age, height, and weight was superior to a weight-only model in predicting UFH dosage. Target-range antifactor Xa levels were achieved with the new protocol in 122 (87%) of 140 patients within 24 hours of start of therapy.

CONCLUSION

A UFH dosage protocol based on patient sex, age, height, and weight produced improved initial target antifactor Xa levels compared with a weight-based protocol. The protocol is computerized and easy to apply.