Two Instruments to Determine Activated Partial Thromboplastin Time: Implications for Heparin Monitoring

Taylor, Charles T.; Petros, William P.; Ortel, Thomas L.

doi:10.1592/phco.19.6.383.31039

Cited by 11 publications

(25 citation statements)

References 27 publications

(33 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…4,6,36,52 Five publications using nine different assays have explored the relationship between levels obtained from different types of antifactor Xa assays versus a standard heparin level of 0.2-0.4 unit/ml by protamine titration (Table 3). 20,21,44,53,54 When all the results were examined, the range for the lower end was 0.24-0.35 unit/ml, with five of the nine values clustered at 0.28-0.30 unit/ml. The spread on the upper end was more variable (0.38-0.67 unit/ml), and a much lower value appeared to be equivalent to the 0.4 unit/ml by protamine titration.…”

Section: Antifactor Xa Levels As the Standard For Monitoring Unfractimentioning

confidence: 99%

“…54 Although this variance is of concern, other studies suggest that correlation and agreement among antifactor Xa assays are reasonable and that it is quantitatively less than that demonstrated with the aPTT. 35,53 For example, in one study, plasma samples from 44 inpatients who were receiving UFH were used to perform a cross-validation study in four CAP-accredited laboratories using a variety of aPTT and antifactor Xa reagents and instruments. 35 The authors found that compared with the aPTT, the antifactor Xa assay demonstrated superior interlaboratory correlation in five of six pairwise comparisons among individual laboratories.…”

Section: Antifactor Xa Levels As the Standard For Monitoring Unfractimentioning

confidence: 99%

See 1 more Smart Citation

Antifactor Xa Levels versus Activated Partial Thromboplastin Time for Monitoring Unfractionated Heparin

2012

View full text Add to dashboard Cite

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.

show abstract

Section: Antifactor Xa Levels As the Standard For Monitoring Unfractimentioning

confidence: 99%

Section: Antifactor Xa Levels As the Standard For Monitoring Unfractimentioning

confidence: 99%

Antifactor Xa Levels versus Activated Partial Thromboplastin Time for Monitoring Unfractionated Heparin

2012

View full text Add to dashboard Cite

show abstract

“…aprotinin, or that the correlation of APTT with heparin concentration may vary with the APTT instrument (Becker et al, 1999;Taylor et al, 1999;Ferring et al, 2001;Smythe et al, 2001;Choi et al, 2002;Reiss et al, 2002). For these reasons, decisions guided by laboratory APTT results may disagree with decisions based upon POCT APTT results and individual therapeutic APTT ranges must be reported for each instrument if more than one is used for heparin monitoring.…”

Section: Poct: the Apttmentioning

confidence: 99%

Point‐of‐care testing in haemostasis

Perry

Fitzmaurice

Kitchen³

et al. 2010

Br J Haematol

122

View full text Add to dashboard Cite

SummaryPoint-of-care testing (POCT) in haematology has seen a significant increase in both the spectrum of tests available and the number of tests performed annually. POCT is frequently undertaken with the belief that this will reduce the turnaround time for results and so improve patient care. The most obvious example of POCT in haemostasis is the out-ofhospital monitoring of the International Normalized Ratio in patients receiving a vitamin K antagonist, such as warfarin. Other areas include the use of the Activated Clotting Time to monitor anticoagulation for patients on cardio-pulmonary bypass, platelet function testing to identify patients with apparent aspirin or clopidogrel resistance and thrombelastography to guide blood product replacement during cardiac and hepatic surgery. In contrast to laboratory testing, POCT is frequently undertaken by untrained or semi-trained individuals and in many cases is not subject to the same strict quality control programmes that exist in the central laboratory. Although external quality assessment programmes do exist for some POCT assays these are still relatively few. The use of POCT in haematology, particularly in the field of haemostasis, is likely to expand and it is important that systems are in place to ensure that the generated results are accurate and precise.Keywords: point-of-care testing, haemostasis, quality assurance, near patient testing.Point-of-care testing (POCT) is defined as a diagnostic test at or near the site of the patient with the rationale that such testing will result in the rapid generation of results and improve patient care. POCT is frequently undertaken by nonlaboratory personnel both within and outwith the hospital setting and the last 10 years has seen a significant increase in its use, particularly in the field of haemostasis. The importance of POCT is highlighted by a recent publication from the This review summarizes POCT in relation to haemostasis, and complements a previously published guideline by the British Committee for Standards in Haematology on POCT in Haematology (Briggs et al, 2008).

show abstract

“…Samples from patients receiving heparin should be analyzed to determine the aPTT range that corresponds to a "therapeutic" heparin level of either 0.2-0.4 U/ml by protamine titration or 0.3-0.7 U/ml by antifactor Xa analysis.Since Dr. Bussey' s review, clinical investigations of unfractionated heparin have cited significantly different end points for heparin levels using antifactor Xa analysis. [4][5][6] The varying end points highlight another area of controversy surrounding heparin monitoring-the use of heparin levels. What is a therapeutic heparin level, and is 0.2-0.4 U/ml by protamine titration equivalent to 0.3-0.7 U/ml by antifactor Xa analysis?To attempt to answer the above questions, one must have a minimal understanding of the different heparin assays.…”

mentioning

confidence: 99%

“…Since Dr. Bussey' s review, clinical investigations of unfractionated heparin have cited significantly different end points for heparin levels using antifactor Xa analysis. [4][5][6] The varying end points highlight another area of controversy surrounding heparin monitoring-the use of heparin levels. What is a therapeutic heparin level, and is 0.2-0.4 U/ml by protamine titration equivalent to 0.3-0.7 U/ml by antifactor Xa analysis?…”

mentioning

confidence: 99%

Heparin Monitoring: The Confusion Continues

Smythe

Koerber

1999

Pharmacotherapy

View full text Add to dashboard Cite

Earlier this year in Pharmacotherapy, Dr. Henry Bussey reviewed the numerous considerations and limitations of using the activated partial thromboplastin time (aPTT) for heparin monitoring. 1 The recommendations of two recent consensus papers on heparin monitoring from the American College of Chest Physicians and the College of American Pathologists were presented in his article.2, 3 Both organizations suggested that individual laboratories define their own aPTT therapeutic range. Samples from patients receiving heparin should be analyzed to determine the aPTT range that corresponds to a "therapeutic" heparin level of either 0.2-0.4 U/ml by protamine titration or 0.3-0.7 U/ml by antifactor Xa analysis.Since Dr. Bussey' s review, clinical investigations of unfractionated heparin have cited significantly different end points for heparin levels using antifactor Xa analysis. [4][5][6] The varying end points highlight another area of controversy surrounding heparin monitoring-the use of heparin levels. What is a therapeutic heparin level, and is 0.2-0.4 U/ml by protamine titration equivalent to 0.3-0.7 U/ml by antifactor Xa analysis?To attempt to answer the above questions, one must have a minimal understanding of the different heparin assays. The two most common are neutralization and functional assays. Neutralization assays estimate heparin activity by identifying the lowest amount of a substance (protamine sulfate or polybrene) that blocks prolongation of a coagulation test (i.e., thrombin) by heparin. The amount of protamine needed in the test plasma then is compared with the protamine required in a standard sample with a known heparin concentration.Functional assays measure the activity of heparin by inhibiting specific coagulation factors such as Xa or thrombin. This type of assay is based on the binding of heparin, antithrombin, and the activated coagulation factor. Residual activated coagulation factor is measured using enzyme-specific chromogenic or fluorogenic substrates.3, 7 Functional assays using antifactor Xa typically report a higher therapeutic range compared with thrombin-based protamine titration assays. This is due to the differential clearance of high-and low-molecular-weight heparin molecules. Low-molecular-weight molecules that inhibit factor Xa are cleared more slowly and thus accumulate.3 In general, antifactor Xa assays are more automated and are therefore less labor intensive to perform.The majority of data supporting a heparin concentration of 0.2 U/ml as the lower limit of the therapeutic range by protamine titration is limited to animal studies and subanalysis of clinical trials. One study reported inhibition of thrombus progression in a rabbit model with heparin concentrations of approximately 0.2 U/ml by protamine titration.8 A clinical trial comparing continuous intravenous heparin infusion with intermittent subcutaneous heparin in 115 patients found that 13 of 14 episodes of recurrent venous thromboembolism occurred during the first 24 hours in patients with a heparin concentration < ...

show abstract

Two Instruments to Determine Activated Partial Thromboplastin Time: Implications for Heparin Monitoring

Abstract: 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.

Cited by 11 publications

References 27 publications

Antifactor Xa Levels versus Activated Partial Thromboplastin Time for Monitoring Unfractionated Heparin

Antifactor Xa Levels versus Activated Partial Thromboplastin Time for Monitoring Unfractionated Heparin

Point‐of‐care testing in haemostasis

Heparin Monitoring: The Confusion Continues

Contact Info

Product

Resources

About