Type of test Blood

 Normal findings

 APTT: 30-40 seconds

PTT: 60-70 seconds

Patients receiving anticoagulant therapy: 1.5-2.5 times the control value in seconds

Possible critical values

 APTT: > 70 seconds PTT: > 100 seconds

Test explanation and related physiology

 The PTT test is used to assess the intrinsic system and the common pathway of clot formation. PTT evaluates factors I (fibrinogen), II (prothrombin), V, VIII, IX, X, XI, and XII. When any of these factors exist in inadequate quantities, such as in hemophilia A and B or consumptive coagulopathy, PTT is pro longed. Because factors II, IX, and X are vitamin K–dependent factors, biliary obstruction, which precludes GI absorption of fat and fat-soluble vitamins (e.g., vitamin K), can reduce their con centration and thus prolong PTT. Because coagulation factors are made in the liver, hepatocellular diseases will also prolong PTT.

Heparin has been found to inactivate prothrombin (factor II) and prevent the formation of thromboplastin. These actions pro long the intrinsic clotting pathway for approximately 4 to 6 hours after each dose of heparin. Thus heparin is capable of providing therapeutic anticoagulation. The appropriate dose of heparin can be monitored by PTT. Test results are given in seconds, along with a control value. The control value may vary slightly from day to day because of the reagents used.

Recently activators have been added to PTT test reagents to shorten normal clotting time and provide a narrow normal range. This shortened time is called the activated PTT (APTT). Normal APTT is 30 to 40 seconds. Desired ranges for therapeutic anticoagulation are 1.5 to 2.5 times normal (e.g., 70 seconds). The APTT specimen should be drawn 30 to 60 minutes before the patient’s next heparin dose is given. If the APTT is less than 50 seconds, the patient may not be receiving therapeutic anticoagulation and need more heparin. An APTT greater than 100 seconds indicates that too much heparin is being given; the risk of serious spontaneous bleeding exists when the APTT is this high. The effects of heparin can be reversed immediately by the administration of protamine sulfate. Anti-Xa can also be used to monitor heparin dosing and determine dosing of protamine sulfate.

APTT is also used to determine activated protein C (APC) resistance. APC resistance testing is performed in the evaluation of thrombotic patients. A standard APTT test is per formed first in the absence of, and then in the presence of, commercially available APC. The APTT is normally prolonged in the presence of APC because of APC’s anticoagulant inhibiting coagulation factors VIII and V. An abnormality is detected if the APTT is not prolonged. This results from a resistance to APC, most commonly (80%) caused by an abnormal factor V Leiden.

Normal pregnancy has been associated with prolonged APTT times. Factor XI deficiency and antiphospholipid antibody are two major abnormalities identified in pregnant patients with pro longed APTT. These coagulopathies are not usually associated with excessive bleeding or thromboembolism. At the same time, pregnancy or oral contraceptive (OC) use is also associated with prolonged APTT. This is due, in large part, to a factor V mutation (factor V Leiden), which potentiates the prothrombotic effect of OC.

Interfering factors

* Drugs that may prolong PTT test values include antihistamines, ascorbic acid, chlorpromazine, heparin, and salicylates.

Procedure and patient care

 • See inside front cover for Routine Blood Testing.

• Fasting: no

• Blood tube commonly used: blue

• If the patient is receiving heparin by intermittent injection, plan to draw the blood specimen for the APTT 30 minutes to 1 hour before the next dose of heparin.

 • If the patient is receiving continuous heparin, draw the blood at any time.

• Apply pressure to the venipuncture site. Remember that if the patient is receiving anticoagulants or has coagulopathies, the bleeding time will be increased.

• Assess the patient to detect possible bleeding. Check for blood in the urine and all other excretions and assess the patient for bruises, petechiae, and low back pain.

• If severe bleeding occurs, note that the anticoagulant effect of heparin can be reversed by parenteral administration of protamine sulfate.

 Abnormal findings

Increased levels

- Acquired or congenital clotting factor deficiencies (e.g., hypofibrinogenemia, von Willebrand disease, and hemophilia)

- Cirrhosis of the liver

- Vitamin K deficiency

- Disseminated intravascular coagulation (DIC)

- Heparin administration

Decreased levels

- Early stages of DIC

- Extensive cancer

اخر الاخبار

اخبار العتبة العباسية المقدسة

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المجمع العلميّ يُجري اختبارات نظريّة وتطبيقيّة لطلبته في قضاء الحمزة الشرقيّ

لطلبتها وملاكاتها جامعة الكفيل تواصل تنظيم الورشة التدريبية للإسعافات الأولية استعدادًا لزيارة الأربعين

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المزيد

الآخبار الصحية

"شعور لا مفر منه" في الحياة يهدد حياة الملايين بالموت المبكر!

أعراض للخرف قد تظهر في المشي.. كيف نكتشفها؟

ماذا يحدث لسكر الدم عند شرب القهوة؟

سرطان القلب.. لماذا يعد من أندر أنواع السرطانات؟

المزيد

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صهر أردوغان يطلق منصة تواصل جديدة.. تنافس فيسبوك ؟!

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بعد 20 عاما.. رصد أصغر أفعى في العالم مجددا في بربادوس !

ذكر أم أنثى؟.. دراسة تنسف الاعتقاد الشائع حول جنس المولود

المزيد

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