How does heparin affect ptt

The international normalized ratio INR is used to make sure the results from a PT test are the same from one lab to another. In the s, the World Health Organization determined that people undergoing surgery may be at risk of excessive bleeding because different labs had different standardized values than other labs.

The INR result should be the same, regardless of the location where the tests are performed. Blood draws are considered routine, low-risk procedures. While rare, it is possible to have complications from a simple blood draw. If you feel lightheaded during or after a blood draw or the site continues to bleed, let someone at the facility know so they can assist or monitor you as needed. Keep your puncture site covered and clean for a few days and watch for signs of infection pain, redness, heat, swelling, fever, chills over the next couple of days.

Get medical help if signs of an infection develop. After an abnormal PT test result, your healthcare provider may want to run additional tests. If you are not currently taking any medication that affects blood clotting factors, you may need to start taking one to normalize your levels.

If you are taking a medication that affects clotting, your dosage may require an adjustment if your PT is not in the target range. Yes, if you are taking warfarin, certain foods and drinks, that contain vitamin K, like dark leafy greens or green tea, may reduce its effectiveness.

Alcohol or cranberry and grapefruit products can increase the risk of bleeding when taking warfarin. Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life.

How to report results of prothrombin and activated partial thromboplastin times. Clin Chem Lab Med. National Institutes of Health, U. National Library of Medicine: MedlinePlus. Prothrombin time PT. Updated April 2, Cleveland Clinic. Blood clotting disorders hypercoagulable states. Updated April 25, Harvard College, T. Research Letter. April 11, Eberhard W. Report of a Case. Access your subscriptions. Access through your institution. Add or change institution.

Free access to newly published articles. Purchase access. Rent article Rent this article from DeepDyve. Access to free article PDF downloads. Save your search. The use of therapeutic ratios was largely abandoned in favor of PTT therapeutic ranges calibrated by anti-Xa heparin measurements.

Guidelines were developed using data from the McMaster group studies showing a heparin level of 0. Assay comparison studies demonstrated that anti-Xa therapeutic heparin levels corresponding to a protamine assay concentration of 0. Laboratory assay that measures the activity of heparin against the activity of activated coagulation factor X. Antithrombin formerly antithrombin III. A serine protease in blood that acts as a natural anticoagulant.

AT activity increases many fold when bound to heparin. A relative measure of the sensitivity of the PT reagent to the therapeutic effect of the anticoagulant coumadin. International Units. A unit of measurement of a biological substance based on its activity.

Multiple sugar molecules bound together. A pentasaccharide is composed of 5 sugar molecules. A laboratory monitoring heparin therapy with the PTT must establish a therapeutic range using an appropriate technique. For initial creation of a therapeutic range, the CAP recommends 1 collection of plasma samples from patients receiving IV heparin therapy ex vivo samples and 2 analysis by PTT and heparin assay. Laboratories may repeat the same validation process or analyze samples from patients receiving IV heparin therapy by the original PTT reagent lot or method and the new PTT lot and compare the results to determine clinically equivalent response.

The mean difference between the lot used to establish the PTT therapeutic range and a subsequent lot must not exceed 7 seconds. Since each subsequent reagent lot is compared against the preceding lot, laboratories must monitor the sum of differences from the reagent lot used in the original validation to ensure that the cumulative mean PTT difference does not exceed 7 seconds.

Hypothetical comparison of therapeutic ranges established from regression analysis of spiked plasma pools in vitro response: 79 to seconds or specimens from heparinized patients in vivo response: 70 to seconds. Many laboratories will find it challenging to meet the recommendations for validating their laboratory-specific PTT therapeutic ranges.

The most daunting problem is identifying a sufficient number of patients receiving UH therapy, since, as noted previously, LMWH is replacing UH as the heparin of choice for preventing or treating thromboembolism. This situation will be exacerbated as new anticoagulants are approved for use by regulatory agencies. The laboratory must rely on the clinical team to draw specimens at the appropriate interval following bolus doses or dose changes and, since PTT samples may be collected and sent for analysis at all hours of the day and night, identification of a patient receiving UH, sample retrieval, and anti-Xa analysis within sample stability time limits can be an issue.

Finally, the degree of scatter found in a plot of PTT versus heparin concentration leads to very large confidence intervals around the estimated limits of the therapeutic range.

Abandoning the PTT in favor of the anti-Xa assay for monitoring heparin therapy would have the following advantages:. Unlike the PTT, the anti-Xa assay is not affected by under-filled collection tubes—a common preanalytic problem. The anti-Xa assay is not susceptible to interference from elevated concentrations of factor VIII or fibrinogen that result from acute phase reactions.

The anti-Xa assay is not influenced by factor deficiencies, with the possible exception of AT deficiency see below. Most important, there would no longer be a need to establish a PTT therapeutic range, provided the laboratory has informed clinicians that UH therapy must be monitored using the anti-Xa assay rather than the PTT and the clinicians are also informed of the therapeutic range.

Prompt sample processing 1 hour is required to avoid heparin neutralization from platelet factor 4. Despite the limitations of the PTT for monitoring adequacy of heparin therapy, it does represent a measure of the anticoagulant effect of heparin in patients.

The assay underestimates heparin concentration in the presence of significant AT deficiency, although the clinical significance of this finding is controversial. Though the authoritative recommendation for the anti-Xa therapeutic range is 0. There is limited published information on the use of anti-Xa assays for routine monitoring of UH therapy.

One recent study identified patients in a medical intensive care unit who were receiving IV heparin but had no measurable heparin levels by 3 different anti-Xa assays. There are limited published outcomes data evaluating the safety and effectiveness of anti-Xa assays for managing UH therapy. The PTT continues to be the primary test used by laboratories for monitoring IV heparin therapy in spite of known limitations for predicting adequacy of anticoagulation in the treated patient, and the difficulty of establishing and maintaining a validated therapeutic range with each reagent lot or instrument change.

Replacement of UH with LMWH and other new anticoagulants that do not require routine laboratory monitoring will increase the challenges labs face in validating their PTT therapeutic ranges.

Unfractionated heparin therapy is not likely to vanish anytime soon, however, since there is a role for an anticoagulant whose effects are rapidly reversible in the event of bleeding eg, intensive care patients. Therefore, many laboratories may find themselves in the position of attempting to validate their PTT therapeutic ranges but being unable to comply with current accreditation recommendations. In an attempt to acquire sufficient samples, laboratories might decide to 1 collect more than 2 samples from each patient or 2 make do with fewer than 30 samples.

Either of these approaches would have the effect of increasing the inaccuracy of the estimated therapeutic range. Since an elevated PTT correlates poorly with heparin-induced bleeding, 7 , 8 the primary risk of an inaccurate therapeutic PTT range would be thrombosis secondary to inadequate anticoagulation ie, underestimate the elevation of the PTT necessary to achieve therapeutic anticoagulation.

However, the risk of thrombosis may be minimal if patients receive an adequate, weight-based bolus dose of UH, followed by maintenance doses, regardless of the PTT attained. Though largely replaced by low molecular weight heparin, low-dose unfractionated heparin is effective at preventing thrombosis associated with orthopedic surgery, obstetric conditions, trauma surgery, and inflammatory medical conditions.

Because low dose unfractionated heparin is not associated with bleeding risk, there is no requirement for monitoring. If monitoring is desired, the anti-Xa heparin assay provides a more sensitive means than the PTT , and the target range is about 0. Chapter Blood component and pharmacologic therapy of hemostatic disorders. Consultative Hemostasis and Thrombosis. Saunders,