What should ptt be when on heparin

Learn more about laboratory tests, reference ranges, and understanding results. A PTT test is often ordered along with another blood test called prothrombin time. A prothrombin time test is another way to measure clotting ability.

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. What is a PTT partial thromboplastin time test? What is it used for? A PTT test is used to: Check the function of specific coagulation factors. If any of these factors are missing or defective, it can mean you have a bleeding disorder.

Bleeding disorders are a group of rare conditions in which blood doesn't clot normally. The most well-known bleeding disorder is hemophilia. Find out if there is another reason for excessive bleeding or other clotting problems.

These include certain autoimmune diseases that cause the immune system to attack coagulation factors. Monitor people taking heparin , a type of medicine that prevents clotting. In some bleeding disorders, the blood clots too much, rather than too little.

This can cause heart attacks , strokes , and other life-threatening conditions. But taking too much heparin can cause excessive and dangerous bleeding. Why do I need a PTT test? You may need a PTT test if you: Have unexplained heavy bleeding Bruise easily Have a blood clot in a vein or artery Have liver disease , which can sometimes cause problems with blood clotting Will be getting surgery.

Surgery can cause blood loss, so it's important to know if you have a clotting problem. Have had multiple miscarriages Are taking heparin. 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. Anti-Xa assays represent an attractive alternative to the PTT for UH monitoring; however, minimal outcomes data and greater expense are limiting factors.

While the cost of Anti-Xa assays might decrease with higher test volumes, prospective clinical outcomes data are not likely to be forthcoming because of the waning utilization of UH. Nonetheless, laboratories may elect to switch to anti-Xa heparin monitoring based on the outcomes data currently available.

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View Large Download. Small subcutaneous doses of heparin in prevention of venous thrombosis. Hudcova JTalmor D Life-threatening hemorrhage following subcutaneous heparin therapy. Prolonged activated partial thromboplastin time in thromboprophylaxis with unfractionated heparin in patients undergoing cesarean section. See More About Anticoagulation.

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