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

Normal aPTT in children with mild factor XI deficiency

It has been suggested that persons with factor XI deficiency can have a normal activated partial thromboplastin time (aPTT). This notion is based on limited data, especially in children. Because of the central role the aPTT plays in diagnostic algorithms for bleeding disorders, it is important to know if a normal aPTT eliminates the need for factor XI activity testing. Our institutional database contains seven children with factor XI deficiency, of whom four have a normal aPTT. This supports the hypothesis that children with factor XI deficiency can have a normal aPTT. Clinicians may wish to consider this evidence when evaluating children with abnormal bleeding.

Point of Care: Diagnostics in Hemostasisthe Wrong Direction?

Point-of-care-testing (POCT) is performance of a laboratory assay outside the laboratory by nontrained personnel. The advantages of POCT are: more rapid medical decisions, avoidance of long sample transports, and small samples. The disadvantages of POCT are: no laboratory personnel, insufficient calibration, quality control and maintenance, poor documentation, high costs, difficult comparability POCT/central laboratory. Therefore, disposing of a 24-hour central laboratory, the POCT spectrum should be limited to the vital parameters: K+, Ca++, Na+, glucose, creatinine, blood gases, hemoglobin or hematocrit, NH3, lactate. POCT offers no advantages, if the hospital has a rapid transport system such as a pneumatic delivery to the central laboratory. The rapid diagnosis of the acute hemostasis state of a patient should be performed in the 24-hour central laboratory that is connected to all hospital wards via a good pneumatic delivery.

Evaluation of a bedside device to assess the activated partial thromboplastin time for heparin monitoring in infants

To determine the relationship between the activated partial thromboplastin time (aPTT) measured with a standard laboratory assay and the aPTT measured with a bedside device in infants on heparin therapy after cardiothoracic surgery. Twenty infants aged below 1 year who were on heparin therapy were included. Exclusion criteria were prematurity, dysmaturity and the use of anticoagulants other than heparin. Nineteen samples were obtained from four adults in intensive care who were on heparin. The aPTT values were analyzed with the Coaguchek Pro/DM bedside device (aPTTbed) and compared with the aPTT values obtained from the laboratory Electra 1800C coagulation analyzer (aPTTlab). Correlation analysis was performed by linear regression. The agreement was calculated using Bland-Altman analysis. The correlation coefficient of samples obtained from infants was lower (r = 0.48) compared with samples from adults (r = 0.85). A substantial positive bias (27 s) and scatter [95% confidence interval (CI) -11; +65 s) was found. The bias showed a genuine trend to increase at higher aPTT values (r = 0.90; P < 0.001). The bedside device overestimates the aPTT in infants treated with heparin. The disagreement between the bedside device and laboratory increases at higher aPTTs. Bedside devices should not be used to monitor heparin therapy in infants in intensive care.

INR comparison between the CoaguChek® S and a standard laboratory method among patients with self-management of oral anticoagulation

INTRODUCTION

Portable coagulation monitors have been developed to measure International Normalised Ratio (INR) in orally anticoagulated patients using capillary whole blood from a finger stick. Because of unsatisfactory precision of some of the monitors in comparison with laboratory methods new devices are being developed. In the present study we compared INR determination with the CoaguChek S device with a standard laboratory method among patients with self-management of oral anticoagulation (OAC).

METHODS

Two hundred and forty-two patients performing self-management of OAC were enrolled into this study. Parallel INR measurements were performed within one hour. Capillary INR measurements (INRcap) were done by the patients with the CoaguChek S and venous INR (INRven) by qualified medical staff using a standard laboratory method.

RESULTS

We found a correlation coefficient (r(S)) of 0.85 (95% CI: 0.81-0.88) among the 242 patients between INRven and INRcap. In 84.4% of the INR parallel measurements the difference between the two values was below 0.5 INR units. In only 2 of 242 cases the difference was >1 INR unit (1.1 and 1.3). The slope of the Passing Bablok regression line was 0.91 (95% CI: 0.83-1.0) and the y-intercept 0.06 (95% CI: -0.20-0.25). Agreement between both methods was 90.5% (95% CI: 86.8-94.2) and standard-agreement even 97.1% (95% CI: 95-99.2).

CONCLUSIONS

INR measurement with CoaguChek S device by trained patients revealed reliable results in comparison to the values obtained with a standard laboratory method.

Point of care management of heparin administration after heart surgery

OBJECTIVES

Determination of activated partial thromboplastin time (aPTT) is used in coagulation management after heart surgery. Results from the central laboratory take long to be obtained. We sought to shorten the time to obtain coagulation results and the desired coagulation state and to reduce blood loss and transfusions using point of care (POC) aPTT determination.

DESIGN

Randomized, controlled trial.

SETTING

University-affiliated 20-bed surgical ICU.

PATIENTS AND PARTICIPANTS

Forty-two patients planned for valve surgery (Valves) and 84 for coronary artery bypass grafting (CABG) with cardiopulmonary bypass.

INTERVENTIONS

Valves and CABG were randomized to postoperative coagulation management monitored either by central laboratory aPTT (Lab group) or by POC aPTT (POC group). Heparin was administered according to guidelines.

MEASUREMENTS AND RESULTS

POC aPTT results were available earlier than Lab aPTT after venipuncture in Valves (3 +/- 2 vs. 125 +/- 68 min) and in CABG (3 +/- 4 vs. 114 +/- 62 min). Heparin was introduced earlier in the POC group in Valves (7 +/- 23 vs. 13 +/- 78 h, p = 0.01). Valves of the POC group bled significantly less than Valves in the Lab group (647 +/- 362 ml vs. 992 +/- 647 ml, p < 0.04), especially during the first 8 h after ICU admission. There was no difference in bleeding in CABG (1074 +/- 869 ml vs. 1102 +/- 620, p = NS). In Valves, fewer patients in the POC group than in the Lab group needed blood transfusions (1/21 vs. 8/21; p = 0.03). No difference was detected in CABG.

CONCLUSIONS

In Valves in the POC group the time to the desired coagulation state was reduced, as was the thoracic blood loss, reducing the number of patients transfused. This improvement was not observed in CABG. Side effects were similar in the two groups.

Point-of-care antithrombotic monitoring in children

INTRODUCTION

The use of oral anticoagulant therapy is increasing in children. Managing anticoagulant therapy in children presents unique challenges, including poor venous access. The advent of point-of-care (POC) monitoring of anticoagulant therapy offers a potential solution to this challenge. This paper reviews the published literature relating to POC monitoring of oral anticoagulant therapy in children.

MATERIALS AND METHODS

A Medline search was conducted and identified key publications. Papers were reviewed with respect to their objectives, populations and POC device investigated. Study limitations were identified.

RESULTS

Five publications and one abstract were identified, reporting studies using five different POC monitors. Three studies had a strong clinical management focus. Outcome measures assessed included target therapeutic range achievement and frequency of adverse events. Correlation between POC and laboratory-based results ranged from 0.83 to 0.96. Home monitoring and self-management using POC monitors were both reported to be preferred compared to standard laboratory testing.

CONCLUSIONS

POC monitoring of oral anticoagulant therapy in children offers considerable advantages. The reviewed literature would suggest such monitoring can be performed accurately and reliably. The impact of quality control issues, such as calibration of thromboplastin ISI in POC devices, has not been explored in a paediatric population. Further studies are needed to clarify such issues and confirm the safety, reliability and efficacy of POC monitoring of oral anticoagulant therapy in children, including its home monitoring and self-management programs.

Comparison of laboratory and immediate diagnosis of coagulation for patients under oral anticoagulation therapy before dental surgery

Background

Dental surgery can be carried out on patients under oral anticoagulation therapy by using haemostyptic measures. The aim of the study was a comparative analysis of coagulation by laboratory methods and immediate patient diagnosis on the day of the planned procedure.

Methods

On the planned day of treatment, diagnoses were carried out on 298 patients for Prothrombin Time (PT), the International Normalised Ratio (INR), and Partial Thromboplastin Time (PTT). The decision to proceed with treatment was made with an INR < 4.0 according to laboratory results.

Results

Planned treatment did not go ahead in 2.7% of cases. Postoperatively, 14.8% resulted in secondary bleeding, but were able to be treated as out-patients. 1.7% had to be treated as in-patients. The average error between the immediate diagnosis and the laboratory method: 95% confidence interval was -5.8 ± 15.2% for PT, -2.7 ± 17.9 s for PTT and 0.23 ± 0.80 for INR. The limits for concordance were 9.4 and -21.1% for PT, 15.2 and -20.5 s for PTT, and 1.03 and -0.57 for INR.

Conclusion

This study showed a clinically acceptable concordance between laboratory and immediate diagnosis for INR. Concordance for PT and PTT did not meet clinical requirements. For patients under oral anticoagulation therapy, patient INR diagnosis enabled optimisation of the treatment procedure when planning dental surgery.

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.

Comparison of four commercially available activated partial thromboplastin time reagents using a semi-automated coagulometer

Large numbers of activated partial thromboplastin time (aPTT) reagents are sold in the market. The phospholipid content and its source, nature and the amount of activators are highly varied in different aPTT reagents. The present study was undertaken to evaluate which of the four aPTT reagents commonly used is suitable as an all-purpose reagent for a modest haemostasis laboratory. Four aPTT reagents (reagent A, Platelin LS; reagent B, Silimat; reagent C, Actin FSL; reagent D, CK Prest) were tested against 75 different plasmas obtained from normal patients as well as from patients with different haemostatic problems. All the tests were conducted by one of us (S.S.) in duplicates. Different aPTT reagents missed different proportions of mild factor VIII and factor IX deficiency (36.4, 18.2, 4.6 and 13.6% for reagents A, B, C and D, respectively) and showed abnormal results with normal plasmas (i.e. more than 5 s prolongation) (29.2, 25, 8.3 and 12.5% for reagents A, B, C and D, respectively). All the reagents faithfully picked up moderate and severe factor VIII and factor IX deficiency. There was no difference among the four aPTT reagents regarding their ability to prolong aPTT to therapeutic dosage of heparin or in their ability to give comparable factor VIII or factor IX levels in one-stage aPTT-based assays. There were differences in aPTT reagents in their ability to pick up mild deficiency of coagulation factor VIII and factor IX. Some reagents showed abnormal aPTT results in mild cases of factor VIII and factor IX deficiency without producing a large number of falsely prolonged aPTT with normal plasma.

Point of care measurement of lepirudin and heparin anticoagulation during systemic inflammation

BACKGROUND

The number of indications for recombinant human hirudin lepirudin therapy has increased in recent years, and now includes acute coronary syndromes and heparin-induced thrombocytopenia. Hence, point of care monitoring appears desirable for therapy with lepirudin. As CoaguChek Plus (CCP) provides a rapid bedside test to monitor therapy with other anticoagulants, we aimed to determine its suitability for lepirudin therapy.

METHODS

Forty-four healthy volunteers received a 2 ng/kg endotoxin infusion (to induce coagulation) together with clinically relevant doses of lepirudin or heparin in a prospective, placebo-controlled, randomised fashion. Measurements of CCP-partial thromboplastin time (aPTT) were compared to laboratory STA-aPTT.

RESULTS

As expected, baseline values of CCP-aPTT were shorter than STA-aPTT. Lepirudin increased CCP-aPTT 3-fold, and STA-aPTT 2-fold 1 h after bolus infusion. During lepirudin infusion, the correlation between CCP-aPTT and STA-aPTT was excellent (r=0.86-0.92). Both methods were equally sensitive to over-anticoagulation with heparin. Acute systemic inflammation had little effects on CCP-aPTT.

CONCLUSION

CCP-aPTT is suitable for longitudinal point of care monitoring of lepirudin therapy. As baseline values of CCP-aPTT are shorter than STA-aPTT, it is recommended not to indiscriminately change between methods in the follow-up of individual patients.

Point-of-care versus laboratory monitoring of patients receiving different anticoagulant therapies

STUDY OBJECTIVE

To compare point-of-care and standard hospital laboratory assays for monitoring patients receiving single or combination anticoagulant regimens.

DESIGN

Prospective analysis.

SETTING

Nursing units and clinics at a large, community hospital.

PATIENTS

One hundred fifty patients receiving anticoagulants for cardiac, vascular, orthopedic, or cancer indications. Thirty patients were enrolled into each treatment group: warfarin, enoxaparin, heparin, warfarin plus enoxaparin, and warfarin plus heparin.

INTERVENTION

Capillary and venous blood samples were collected once in each patient for simultaneous measurement of international normalized ratio (INR) and activated partial thromboplastin time (aPTT) by both assays.

MEASUREMENTS AND MAIN RESULTS

Mean differences in paired INR and paired aPTT by point-of-care and standard assays were small, but 95% confidence intervals were wide. The INR differences were greater for the warfarin plus heparin group than for the warfarin group or warfarin plus enoxaparin group; clinical decision agreement was 47% for warfarin plus heparin, 73% for warfarin, and 93% for warfarin plus enoxaparin. The aPTT difference was greater for the warfarin plus heparin than for the heparin group; however, clinical decision agreement, 67% and 70%, respectively, was similar.

CONCLUSIONS

Point-of-care methods showed limited agreement with standard hospital laboratory assays of coagulation for all treatment groups. For INR values, significantly greater disagreement was noted between the assay methods for the warfarin plus heparin group compared with the warfarin group, but the agreement was similar for the warfarin and warfarin plus enoxaparin groups. Our data indicate that the point-of-care assays should not be considered interchangeable with standard laboratory assays.

Point of care testing in the emergency department

Point of care (POC) testing in the Emergency Department (ED) is becoming more common. The implementation and maintenance of POC testing in the ED, however, is a complex issue. We performed a systematic review of the English language literature published between 1985 and June 2001 with a focus on POC testing and ED application. Articles that addressed the following were included in the review: implementation of POC testing, maintenance and regulation of POC testing, and application of POC testing. Current POC technology has been found to be reliable in various patient care settings, including the ED. Cost and connectivity issues are complex and difficult to assess, making these the greatest barriers to the full acceptance of POC testing in the ED. Patient care issues must be weighed against the cost of implementing POC testing and supporting the infrastructure needed to maintain this technology in the ED.

Point of care and central laboratory determinations of the aPTT are not interchangeable in surgical intensive care patients

PURPOSE

The objective of the study was to compare a bedside whole blood activated partial thromboplastin time (aPTT) performed by a point of care (POC) apparatus (CoaguCheck(R) Pro) in surgical intensive care (SIC) patients with a conventional aPTT obtained from the central laboratory.

METHODS

The prospective concomitant measurements of the two aPTT were performed in 233 samples from 46 consecutive patients admitted after cardiovascular or major abdominal surgery.

RESULTS

Inter-operator, inter-instrument and inter-cartridge variability of the new device measured in three healthy volunteers and in nine patients in stable condition (controls) was low (F test: P=0.86). The agreement by Bland and Altman between POC and central laboratory aPTT (-20.2 +/- 18.8 sec) was not satisfactory. The agreement between POC and central laboratory aPTT in patients after surgery was worst (-17 +/- 33.1 sec). Heparin treatment or timing of blood sampling after intensive care admission (<48 hr vs >48 hr) did not influence the agreement. The correlation between POC or central laboratory aPTT and anti-factor Xa activity was poor (r(2) 0.077 and 0.181 respectively). The test which correlated the best to heparin doses was anti-factor Xa activity (r(2) 0.714).

CONCLUSION

POC aPTT and central laboratory aPTT showed a poor agreement in SIC patients admitted after surgery, although in healthy volunteers or in control patients, this agreement was better. The best test to monitor heparin treatment in this setting was anti-factor Xa activity.

Disagreement between bedside and laboratory activated partial thromboplastin time and international normalized ratio for various novel anticoagulants

During studies on warfarin, heparin and various anticoagulants with novel mechanisms of action, the activated partial thromboplastin time (aPTT) and the (apparent) international normalized ratio (INR) from a bedside monitor (Coagucheck Plus(R)) were compared with laboratory assay results. Data were compared using the Bland and Altman method of comparison where systematic differences result in significant slopes of the regression line. During heparin treatment, the bedside monitor largely underestimated the aPTT (slope = -0.80). During treatment with the direct thrombin inhibitor napsagatran (slope = 0.99), the pentasaccharides Org31540/SR90107A (slope = 0.77) and SanOrg34006 (slope = 0.35), and warfarin (slope = 0.60), the bedside monitor underestimated the aPTT at lower aPTT levels, while at higher aPTT levels it overestimated the laboratory values. The bedside monitor slightly overestimated the INR during treatment with warfarin (slope = 0.33). Apparent INR was largely overestimated during treatment with Org31540/SR90107A (slope = 1.38), SanOrg34006 (slope = 0.97), Napsagatran (slope = 1.23), and recombinant tissue factor pathway inhibitor (slope = 1.48, P < 0.001 for all regression lines). These results indicate that a substantial disagreement in aPTT or (apparent) INR exists between the bedside monitor and laboratory assay during treatment with the studied 'classic' and novel anticoagulants. The amount of disagreement depended on the anticoagulant given.

Accuracy, precision, and quality control for point-of-care testing of oral anticoagulation

Oral anticoagulant (OAC) therapy is usually monitored by noting changes in a tissue factor-induced coagulation time ("prothrombin time") test on whole blood or plasma and expressed as an International Normalized Ratio (INR). Current point-of-care (POC) instruments for monitoring OAC therapy display both the calculated prothrombin time (PT) and the INR. Although many attempts have been made to improve the accuracy and precision of INR determinations in daily practice, it is impossible to eliminate all uncertainty because the PT test is sensitive to multiple factors in the patient's blood specimen. The accuracy of the average INR determined with a POC instrument depends on its calibration against reference methods. Quality control (QC) materials for POC devices are different from patients' samples and may not exactly reflect the real clinical situation. Nevertheless, internal and external QC schemes for POC devices are valuable to investigate their performance in daily practice. Calibration can be improved by direct comparison of a POC system against an established international reference preparation method. In general, the precision of the INR measured with a POC device is slightly lower than the precision achieved with available automated laboratory instruments. The greater imprecision should be weighed against the clinical advantages of a POC testing device.