A comparison of five devices for the bedside monitoring of heparin therapy

An ex vivo comparison of partial thromboplastin time and activated clotting time for heparin anticoagulation in an ovine model

BACKGROUND

Sheep are a primary model of mechanical circulatory support (MCS) with heparin anticoagulation therapy frequently being monitored by activated clotting time (ACT) due to ease and cost. In patients undergoing long-term heparin therapy, other anticoagulation monitoring strategies, such as activated partial thromboplastin time (aPTT), have proven to be more reliable indicators for the adequacy of anticoagulation, frequently determined by heparin concentration. As there is a paucity of similar studies in sheep, we sought to investigate the correlation between heparin concentration and ACT and aPTT using whole sheep blood in an ex vivo model.

METHODS

Fresh whole blood was serially drawn from an adult female Dorset-hybrid sheep and aliquots were placed into tubes containing heparin saline solutions with concentrations ranging from 0 to 7.81 U heparin per mL of whole blood. ACT and aPTT values were measured on each of the samples. The experiment was performed four times with the same animal. A simple linear regression was performed to determine correlation, and subgroup analysis was performed on low versus high heparin concentrations typically seen in human patients on long-term MCS, such as extracorporeal membrane oxygenation (ECMO), versus cardiopulmonary bypass, respectively.

RESULTS

aPTT measurements versus the heparin concentration had an R²  = 0.7295. ACT measurements versus the heparin concentration had a R²  = 0.4628. aPTT measurements versus the ACT measurements had a R²  = 0.2974. The strength of the correlation between aPTT and heparin concentration increased at low heparin concentrations (R²  = 0.8392).

CONCLUSION

aPTT had a more reliable correlation to heparin concentration and thus anticoagulation level than ACT. This was particularly true at lower heparin concentrations, similar to ranges seen for patients on ECMO. The correlation between aPTT and ACT values was poor. Further in vivo studies should be performed to confirm our results.

Acute Kidney Injury and Extracorporeal Membrane Oxygenation: Review on Multiple Organ Support Options

Extracorporeal membrane oxygenation (ECMO) is a temporary life support system used to assist patients with life-threatening severe cardiac and/or respiratory insufficiency. Patients requiring ECMO can be considered the sickest patients admitted to the intensive care unit (ICU). Acute kidney injury (AKI) represents a frequent complication during ECMO, affecting up to 70% of patients, with multifactorial pathophysiology and an independent risk factor for mortality. Severe AKI requiring Continuous Renal Replacement Therapy (CRRT) occurs in 20% of ECMO patients, but multiple indications and different timing may imply a significantly higher application rate in different centers. CRRT can be run in parallel to ECMO through different vascular access, or it can be conducted in series by connecting the circuits. Anticoagulation of ECMO is typically managed with systemic heparin, but several approaches can be applied for the CRRT circuit, from no anticoagulation to the addition of intra-filter heparin or regional citrate anticoagulation. The combination of CRRT and ECMO can be considered a form of multiple organ support therapy, but this approach still requires optimization in timing, set-up, anticoagulation, prescription and delivery. The aim of this report is to review the pathophysiology of AKI, the CRRT delivery, anticoagulation strategies and outcomes of patients with AKI treated with ECMO.

Fluorescence-based blood coagulation assay device for measuring activated partial thromboplastin time

The measurement of blood clotting time is important in a range of clinical applications such as assessing coagulation disorders and controlling the effect of various anticoagulant drug therapies. Clotting time tests essentially measure the onset of clot formation which results from the formation of fibrin fibers in the blood sample. However, such assays are inherently imprecise due to the highly variable nature of the clot formation process and the sample matrix. This work describes a clotting time measurement assay which uses a fluorescent probe to very precisely detect the onset of fibrin clot formation. It uses a microstructured surface which enhances the formation of multiple localized clot loci and which results in the abrupt redistribution of the fluorescent label at the onset of clot formation in both whole blood and plasma. This methodology was applied to the development of an activated partial thromboplastin time (aPTT) test in a lateral flow microfluidic platform and used to monitor the effect of heparin dosage where it showed linearity from 0 to 2 U/mL in spiked plasma samples (R(2)=0.996, n = 3), correlation against gold standard coagulometry of 0.9986, and correlation against standard hospital aPTT in 32 patient samples of 0.78.

Anticoagulation and coagulation management for ECMO

Advances in extracorporeal membrane oxygenation (ECMO) management have helped to reduce complications compared with its inception but they remain high. The principal causes of mortality and morbidity are bleeding and thrombosis. The nonbiologic surface of an extracorporeal circuit provokes a massive inflammatory response leading to consumption and activation of procoagulant and anticoagulant components. The vast differences in neonatal and adult anticoagulation and transfusion requirements demands tremendous clinical knowledge to provide the best care. Increased use of thrombelastogram will complement other methods currently being used to improved care. Methods to recognize the level of thrombin formation at the bedside could help reduce neurologic complications. ECMO requires a multidisciplinary team approach to achieve the best outcomes.

Anticoagulation Monitoring Part 2: Unfractionated Heparin and Low-Molecular-Weight Heparin

OBJECTIVE

To review the availability, mechanisms, limitations, and clinical application of point-of-care (POC) devices used in monitoring anticoagulation with unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs).

DATA SOURCES

Articles were identified through a MEDLINE search (1966–August 2004), device manufacturer Web sites, additional references listed in articles and Web sites, and abstracts from scientific meetings.

STUDY SELECTION AND DATA EXTRACTION

English-language literature from clinical trials was reviewed to evaluate the accuracy, reliability, and clinical application of POC monitoring devices.

DATA SYNTHESIS

The activated partial thromboplastin time (aPTT) and activated clotting time (ACT) are common tests for monitoring anticoagulation with UFH. Multiple devices are available for POC aPTT, ACT, and heparin concentration testing. The aPTT therapeutic range for UFH will vary depending upon the reagent and instrument employed. Although recommended by the American College of Chest Physicians Seventh Conference on Antithrombotic and Thrombolytic Therapy, establishing a heparin concentration–derived therapeutic range for UFH is rarely performed. Additional research evaluating anti-factor Xa monitoring of LMWHs using POC testing is necessary.

CONCLUSIONS

Multiple POC devices are available to monitor anticoagulation with UFH. For each test, there is some variability in results between devices and between reagents used in the same device. Despite these limitations, POC anticoagulation monitoring of UFH using aPTT and, more often, ACT is common in clinical practice, particularly when evaluating anticoagulation associated with interventional cardiology procedures and cardiopulmonary bypass surgery.

Near-patient testing for coagulopathy after cardiac surgery

BACKGROUND

We assessed the accuracy and precision of a new near-patient testing system (Hemochron Response) by measuring prothrombin time and activated partial thromboplastin time (PT and APTT) in 50 patients undergoing cardiac surgery using cardiopulmonary bypass and comparing the results with laboratory assays.

METHODS

Blood samples were taken at the beginning of surgery and the PT and APTT was measured both in the laboratory and by the Hemochron Response. The tests were repeated 30 min after reversal of heparin with protamine.

RESULTS

Before bypass, the bias for PT was only +0.34, with small 95% limits of agreement. Making the same measurements after bypass, the Hemochron Response under-read and the bias was -3.27, with an increase of the 95% limits of agreement. With the APTT, the bias and the 95% limits of agreement were greater before bypass, and became even wider after bypass.

CONCLUSIONS

We found good agreement in the PT and clinically acceptable levels of agreement in the APTT during the pre-bypass period. After bypass, bias became greater for both PT and APTT and the limits of agreement could be clinically unacceptable.

The use of the activated clotting time for monitoring heparin therapy in critically ill patients

OBJECTIVE

To determine the correlation between activated clotting time (ACT) and activated partial thromboplastin time (aPTT) in patients receiving intravenous unfractionated heparin therapy, and the accuracy of the ACT in predicting the level of anticoagulation.

DESIGN

Paired aPTT and ACT measurements were obtained from a convenience sample of critically ill patients requiring intravenous unfractionated heparin. The aPTT was determined in the hospital laboratory and ACT measurements were performed with a portable device.

SETTING

The intensive care unit of Ghent University Hospital, a tertiary care facility with 54 beds.

PATIENTS AND PARTICIPANTS

Twenty-eight patients were studied prospectively; a total of 105 paired samples were obtained. The indication for heparin therapy was cerebral ischemia in 8, various cardiac conditions in 10, pulmonary embolism in 3, continuous hemofiltration in 3, and peripheral arterial thrombosis in 4.

RESULTS

There was a significant correlation between aPTT and ACT. Analysis of variance showed a significant difference in ACT between different levels of anticoagulation, aPTT shorter than 60 s (group 1), aPTT 60-90 s (group 2), and aPTT longer than 90 s (group 3): 142+/-16.7 s in group 1 vs. 155+/-29.6 and 192+/-39.1 in groups 2 and 3.

CONCLUSIONS

The correlation between the aPTT and the ACT in this ICU setting is poor; ACT cannot differentiate between low and therapeutic levels of anticoagulation. The use of the ACT for monitoring low to moderate doses of heparin in ICU patients cannot be recommended.

Correlation between activated clotting time and activated partial thromboplastin times

OBJECTIVE

To evaluate the correlation between clotting time tests and heparin concentration, the correlation between activated clotting time (ACT) and activated partial thromboplastin time (aPTT) results, and to compare the clinical decisions based on ACT results with those based on aPTT results.

METHODS

Retrospective evaluation of a large database containing heparin concentrations, ACT results (1 device), and aPTT results (3 different instruments: 2 bedside, 1 laboratory-based). Correlations between heparin concentrations and clotting time tests and between ACT results and aPTT results were determined. Clinical decisions regarding heparin dosage adjustments based on ACT results were compared with those based on aPTT results.

RESULTS

Correlations between clotting time tests and heparin concentrations were r = 0.72 for ACT and r = 0.74-0.86 for the aPTT instruments. The laboratory-based aPTT had the highest correlation to heparin concentrations. The correlation between ACT and aPTT results ranged from r = 0.64-0.67. Heparin dosage adjustment decisions based on ACT results agreed with decisions based on aPTT results 59-63% of the time.

CONCLUSIONS

The laboratory-based aPTT has a stronger correlation to heparin concentration than the bedside-based aPTT and ACT. The correlation between ACT and aPTT was similar among 3 different aPTT instruments. Decisions to adjust heparin therapy based on ACT results differed from decisions based on aPTT results more than one-third of the time.

Monitoring high-dose heparin levels by ACT and HMT during extracorporeal circulation: diagnostic accuracy of three compact monitors

The correct monitoring of heparin therapy and its reversal determines the successful conduct of cardiovascular surgery with extracorporeal circulation (ECC). The activated coagulation time (ACT) and the heparin management test (HMT) are the most frequently used tests in the operating room. Three compact monitors for ACT or HMT are here evaluated. Forty samples were obtained, at 10-min intervals, from eight patients during ECC. The ACT or HMT was immediately performed using: Hemochron juniors ACT, CoaguCeck Pro (ACT) and Rapid Point Coag (HMT). Data were compared between them and with the heparin levels, measured as anti-Xa. The simple least squares linear regression among, respectively, Hemochron Junior ACT, CoaguCeck Pro ACT, Rapid Point Coag HMT and anti-Xa activity were i=452.3, s=15.2, Sy/x=37.5, r=0.18; i=411.9, s=22.1, Sy/x=48.7, r=0.21 and i=479.4, s=9.0, Sy/x=9.3; r=0.41. CoaguCeck Pro ACT results were above the upper detection limit (500 s) in 37 of 40 determinations. The comparison between ACT Hemocron and HMT Rapid Point Coag shows i=35.7, s=0.9, Sy/x=35.4, r=0.68, with a bias of 29.0 s (CI: 17.9-40.1), 95% of agreement between -41.5 s (CI: -60.7 to -22.3) and 99.5 s (CI: 80.4-118.7). Taking a concentration of 2.0 U/ml of heparin to discriminate between high- and low-risk conditions, receiver-operator characteristic (ROC) curve was used to rank the performance of the methods. Areas under the ROC curve+/-SE for Hemochron Junior ACT and Rapid Point Coag HMT were 0.629+/-0.097 and 0.543+/-0.096. The results obtained by HMT appear similar to those obtained by the ACT for monitoring high-dose heparin therapy in patients undergoing ECC. HMT appeared to perform better than ACT in measuring the heparin effect, while the ROC analysis gives a little more accuracy for ACT. Neither of the two methods is able to achieve enough evidence of diagnostic accuracy. Since these tests are widely used, and there are no laboratory alternatives, a real comparison with the outcome of the patients should be helpful for an evidence-based evaluation of these point-of-care tests.

Evaluation of a point-of-care coagulation analyzer for measurement of prothrombin time, activated partial thromboplastin time, and activated clotting time in dogs

OBJECTIVE

To evaluate a point-of-care coagulation analyzer (PCCA) in dogs with coagulopathies and healthy dogs.

ANIMALS

27 healthy and 32 diseased dogs with and without evidence of bleeding.

PROCEDURE

Prothrombin time (PT), activated partial thromboplastin time (aPTT), and activated clotting time (ACT) were determined, using a PCCA and standard methods.

RESULTS

Using the PCCA, mean (+/- SD) PT of citrated whole blood (CWB) from healthy dogs was 14.5+/-1.2 seconds, whereas PT of nonanticoagulated whole blood (NAWB) was 10.4+/-0.5 seconds. Activated partial thromboplastin time using CWB was 86.4+/-6.9 seconds, whereas aPTT was 71.2+/-6.7 seconds using NAWB. Reference ranges for PT and aPTT using CWB were 12.2 to 16.8 seconds and 72.5 to 100.3 seconds, respectively. Activated clotting time in NAWB was 71+/-11.8 seconds. Agreement with standard PT and aPTT methods using citrated plasma was good (overall agreement was 93% for PT and 87.5% for aPTT in CWB). Comparing CWB by the PCCA and conventional coagulation methods using citrated plasma, sensitivity and specificity were 85.7 and 95.5% for PT and 100 and 82.9% for aPTT, respectively. Overall agreement between the PCCA using NAWB and the clinical laboratory was 73% for PT and 88% for aPTT. Using NAWB for the PCCA and citrated plasma for conventional methods, sensitivity and specificity was 85.7 and 68.4% for PT and 86.7 and 88.9% for aPTT, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

The PCCA detected intrinsic, extrinsic, and common pathway abnormalities in a similar fashion to clinical laboratory tests.

Point-of-care testing apparatus. Measurement of coagulation

Point-of-care testing of coagulation parameters provides a more rapid assessment of test results compared with laboratory testing. A new coagulation monitor (GEM PCL, Instrumentation Laboratory, Kirchheim, Germany) was evaluated. Point-of-care data for activated partial thromboplastin time and prothrombin time (expressed as the international normalised ratio) and turn-around-time were compared. Coagulation parameters were compared in the blood of 57 patients with and without heparin therapy. The point-of-care and laboratory test results showed a bias (SD) of -0.26 (4.55) s for activated partial thromboplastin time and -0.011 (0.150) s for prothrombin time. The average turn-around-time was 3 min for point-of-care testing vs. 52 min for laboratory testing. We conclude that the reliability of point-of-care testing is sufficient for clinical use.

Use of the activated partial thromboplastin time for heparin monitoring

The objectives of the present study were to evaluate the relationship between heparin concentration and activated partial thromboplastin time (aPTT) results, define a heparin concentration-derived therapeutic range for each aPTT instrument, compare aPTT- and heparin concentration-guided dosage adjustment decisions, and compare laboratory- and bedside aPTT-guided decisions. In phase 1, 102 blood samples were analyzed for bedside and laboratory aPTTs and heparin concentration (used to establish aPTT therapeutic range). In phase 2, 100 samples were analyzed in the same manner. Correlations for aPTT compared with heparin ranged from 0.36 to 0.82. Dosage adjustment decisions guided by the aPTT agreed with those based on heparin concentration 63% to 80% of the time. Laboratory and bedside aPTT dosage adjustment decisions agreed 59% to 68% of the time. The correlation of aPTT with heparin concentration and agreement between aPTT- and heparin-guided decisions vary with the aPTT instrument. Decisions guided by laboratory aPTT results often disagree with decisions guided by bedside aPTT results.

Optimal management of bleeding and transfusion in patients undergoing cardiac surgery

Patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) are at increased risk for excessive perioperative blood loss requiring transfusion of blood products. Point-of-care evaluation of platelets, coagulation factors, and fibrinogen can enable physicians to rapidly assess bleeding abnormalities, facilitate the optimal administration of pharmacological and transfusion-based therapy, and also identify patients with surgical bleeding. The ability to reduce the unnecessary use of blood products in this setting has important implications for emerging issues in blood inventory and blood costs. The ability to decrease surgical time, along with exploration rates, has important consequences for health care costs in an increasingly managed health care environment.

Two instruments to determine activated partial thromboplastin time: implications for heparin monitoring

STUDY OBJECTIVE

To measure the difference in therapeutic ranges of activated partial thromboplastin time (APTT) between two laboratory devices.

DESIGN

Prospective, controlled laboratory study.

SETTING

University-affiliated hospital.

PATIENTS

Thirty inpatients receiving intravenous unfractionated heparin for treatment of myocardial infarction, unstable angina, deep venous thrombosis, or pulmonary embolism.

INTERVENTIONS

Therapeutic APTT ranges were determined by a portable (whole blood assay) and a central laboratory device (plasma assay) based on heparin serum concentrations. They were compared with APTT ranges equivalent to 1.5-2.5 times the mean normal determination.

MEASUREMENTS AND MAIN RESULTS

The central laboratory and portable devices produced therapeutic ranges of 61-93 and 56-73 seconds, respectively. Both differed from conventional therapeutic ratios of 1.5-2.5 times the mean normal (41-68 sec). Mean absolute APTT differences between instruments were statistically significant (12 +/- 20 sec, p<0.006), and 58% of paired APTT values differed by more than 10 seconds.

CONCLUSION

A fixed APTT ratio as a goal for monitoring unfractionated heparin may result in significant underanticoagulation. Individual therapeutic APTT ranges must be reported for each instrument if more than one is used for heparin monitoring.

Use of bedside activated partial thromboplastin time monitor to adjust heparin dosing after thrombolysis for acute myocardial infarction: results of GUSTO-I. Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries

BACKGROUND

The safety and efficacy of bedside monitors of activated partial thromboplastin time (aPTT) have not been examined in a large population receiving intravenous heparin after thrombolytic treatment for acute myocardial infarction. We compared outcomes among patients monitored with these devices versus standard monitoring methods.

METHODS AND RESULTS

Investigators chose the bedside device (n = 1713 patients) or their standard method (n = 26,162) for all aPTT measurements at their sites. Clinical outcomes at 30 days, 1-year mortality rate, and aPTT levels at 6, 12, and 24 hours were compared. Bedside-monitored patients had significantly less moderate/severe bleeding (10% vs 12%, P < .01), fewer transfusions (7% vs 11%, P < .001), and a smaller decrease in hematocrit (5.5% vs 6.7%, P < .001) but significantly more recurrent ischemia (22% vs 20%, P = .01). Fewer bedside-monitored patients had subtherapeutic aPTT levels at 12 and 24 hours. Among patients with subtherapeutic levels at 6 and 12 hours, more bedside-monitored patients had therapeutic levels when next monitored. After adjustment for baseline differences, no significant difference in mortality rate was observed in bedside-monitored patients at 30 days (4.3% vs 4.8%, P = .27) and at 1 year (7.1% vs 7.7%, P = .38). The groups had similar rates of reinfarction, shock, heart failure, and stroke.

CONCLUSIONS

This prospective substudy supports the use of bedside monitoring of heparin anticoagulation after thrombolysis.

Evaluation of bedside prothrombin time and activated partial thromboplastin time measurement by coagulation analyzer CoaguCheck Plus in various clinical settings

In the present study CoaguCheck Plus (CCP), a coagulation test system using whole blood, was evaluated with respect to its comparability with widely distributed conventional routine coagulation assays. A correlation of r = 0.997 (p < 0.0001) was found between INR of CCP-prothrombin time (CCP-PT) and Thrombotest (KC-1 analyzer) in patients on oral anticoagulant therapy. A correlation of r = 0.899 (p < 0.001) between CCP-aPTT and Actin ES aPTT (STA analyzer) was found in heparinized patients. Impaired hepatic hepatic coagulation factor synthesis in liver cirrhosis patients was detected by CCP-PT with a sensitivity of 0.75 and by Normotest (STA analyzer) with a sensitivity of 0.92. Those patients with normal CCP-PT values and liver disease had, only mild reductions (> 30% of normals) in coagulation factors II, V, VII or X. CCP-aPTT was also performed in patients with a deficiency in the so called endogenous coagulation factors VIII, IX, XI and XII. CCP-aPTT showed a sensitivity similar to that of Actin FS aPTT in the detection even of mild deficiencies in factors VIII, IX and XII; factor XI deficiency was however detected only in patients with severe (< 12% of normals) disease; lupus anticoagulants were detected with a high sensitivity.

Comparison of bedside and hospital laboratory coagulation studies during and after coronary intervention

The activated clotting time is routinely used to monitor anticoagulation during coronary intervention, whereas the hospital laboratory APTT guides pre- and postprocedure heparin therapy. An optimal coagulation test for patients undergoing percutaneous revascularization would provide a rapid and accurate assessment of anticoagulation throughout a broad range of heparin therapy. We studied the relationships of the bedside whole blood APTT, ACT, and the laboratory APTT in 166 patients undergoing coronary intervation. The whole blood APTT correlated closely with the laboratory APTT (range 18-80 sec) (r = .75), whereas the ACT and laboratory APTT had only a fair correlation (r = .42). Also, the whole blood APTT demonstrated a strong correlation with the ACT throughout the range of heparin therapy for intervention (r = .81). The diagnostic accuracy of the whole blood APTT, based on the receiver operating characteristic curve, was significantly better than that for the ACT in determining the anticoagulation status. The whole blood APTT obtained by bedside monitoring provides a rapid and accurate assessment of anticoagulation throughout the range of heparin dosing associated with coronary intervention. In situations in which an adequate assessment of residual anticoagulation is necessary, the whole blood APTT is superior to the ACT and probably should be the method of choice.