Partial Thromboplastin Time, Activated

Partial Thromboplastin Time, Activated

Synonym/acronym: aPTT, APTT.

Common use

To assist in assessing coagulation disorders and monitor the effectiveness of therapeutic interventions.

Specimen

Plasma (1 mL) collected in a completely filled blue-top (3.2% sodium citrate) tube. If the patient’s hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted.

Normal findings

(Method: Clot detection) 25 to 35 sec. The aPTT is normally prolonged in infants, up to 55 sec, and gradually decreases to the adult range by age 6 mo. Reference ranges vary with respect to the equipment and reagents used to perform the assay.

Description

The activated partial thromboplastin time (aPTT) test evaluates the function of the contact activation pathway, formerly known as intrinsic pathway (factors XII, XI, IX, VIII, prekallikrein, and high molecular weight kininogen) and the common pathway (factors V, X, II, and I) of the coagulation sequence. The aPTT time represents the time required for formation of a firm fibrin clot after tissue thromboplastin reagents and calcium are added to a plasma specimen. The aPTT is abnormal in 90% of patients with coagulation disorders and is useful in monitoring effective inactivation of factor II (thrombin) by heparin therapy. The test is prolonged when there is a 30% to 40% deficiency in one of the factors required or when factor inhibitors (e.g., antithrombin III, protein C, or protein S) are present. The aPTT and prothrombin time (PT) tests assist in identifying the cause of or tendency for bleeding as related to coagulation defects. A comparison between the results of aPTT and PT tests can allow some inferences to be made that a factor deficiency exists. A normal aPTT with a prolonged PT can occur only with factor VII deficiency. A prolonged aPTT with a normal PT could indicate a deficiency in factors XII, XI, IX, VIII, and VIII:C (von Willebrand factor). Factor deficiencies can also be identified by correction or substitution studies using normal serum. These studies are easy to perform and are accomplished by adding plasma from a healthy patient to a sample from a patient suspected to be factor deficient. When the aPTT is repeated and is corrected, or is within the reference range, it can be assumed that the prolonged aPTT is caused by a factor deficiency. If the result remains uncorrected, the prolonged aPTT is most likely due to a circulating anticoagulant. (For more information on factor deficiencies, see the “Coagulation Factors” monograph.)

This procedure is contraindicated for

    N/A

Indications

  • Detect congenital deficiencies in clotting factors, as seen in diseases such as hemophilia A (factor VIII) and hemophilia B (factor IX)
  • Evaluate response to anticoagulant therapy with heparin or coumarin derivatives
  • Identify individuals who may be prone to bleeding during surgical, obstetric, dental, or invasive diagnostic procedures
  • Identify the possible cause of abnormal bleeding, such as epistaxis, hematoma, gingival bleeding, hematuria, and menorrhagia
  • Monitor the hemostatic effects of conditions such as liver disease, protein deficiency, and fat malabsorption

Potential diagnosis

Prolonged in

Afibrinogenemia (related to insufficient levels of fibrinogen, which is required for clotting) Circulating anticoagulants (related to the presence of coagulation factor inhibitors, e.g., developed from long-term factor VIII therapy, or circulating anticoagulants associated with conditions like tuberculosis, systemic lupus erythematosus, rheumatoid arthritis, and chronic glomerulonephritis) Circulating products of fibrin and fibrinogen degradation (related to the presence of circulating breakdown products of fibrin) Disseminated intravascular coagulation (related to increased consumption of clotting factors) Factor deficiencies (related to insufficient levels of coagulation factors) Hemodialysis patients (related to the anticoagulant effect of heparin) Severe liver disease (insufficient production of clotting factors related to liver damage) Vitamin K deficiency (related to insufficient vitamin K levels required for clotting) Von Willebrand’s disease (related to a congenital deficiency of clotting factors)

Critical findings

  • Adults & children Greater than 70 sec
  • Note and immediately report to the health-care provider (HCP) any critically increased or decreased values and related symptoms.

  • It is essential that a critical finding be communicated immediately to the requesting HCP. A listing of these findings varies among facilities.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

  • Important signs to note are prolonged bleeding from cuts or gums, hematoma at a puncture site, bruising easily, blood in the stool, persistent epistaxis, heavy or prolonged menstrual flow, and shock. Monitor vital signs, PTT levels, unusual ecchymosis, occult blood, severe headache, unusual dizziness, and neurological changes until aPTT is within normal range.

Interfering factors

  • Drugs and vitamins such as anistreplase, antihistamines, chlorpromazine, salicylates, and ascorbic acid may cause prolonged aPTT.
  • Anticoagulant therapy with heparin will prolong the aPTT.
  • Copper is a component of factor V, and severe copper deficiencies may result in prolonged aPTT values.
  • Traumatic venipunctures can activate the coagulation sequence by contamination of the sample with tissue thromboplastin and can produce falsely shortened results.
  • Failure to fill the tube sufficiently to yield a proper blood-to-anticoagulant ratio invalidates the results and is reason for specimen rejection.
  • Excessive agitation that causes sample hemolysis can falsely shorten the aPTT because the hemolyzed cells activate plasma-clotting factors.
  • Inadequate mixing of the tube can produce erroneous results.
  • Specimens left unprocessed for longer than 24 hr should be rejected for analysis.
  • High platelet count or inadequate centrifugation will result in decreased values.
  • Hematocrit greater than 55% may cause falsely prolonged results because of anticoagulant excess relative to plasma volume.
  • Incompletely filled collection tubes, specimens contaminated with heparin, clotted specimens, or unprocessed specimens not delivered to the laboratory within 1 to 2 hr of collection should be rejected.

Nursing Implications and Procedure

Potential nursing problems

ProblemSigns & SymptomsInterventions
Bleeding (Related to alerted clotting factors secondary to heparin use or depleted clotting factors)Altered level of consciousness; hypotension; increased heart rate; decreased HGB and HCT; capillary refill greater than 3 sec; cool extremities; blood in urine, stool, sputum; bleeding gums; nosebleed; bruises easily; elevated PTTIncrease frequency of vital sign assessment with variances in results; monitor for vital sign trends; administer blood or blood products as ordered; administer prescribed vitamin K; monitor and trend HGB/HCT; assess skin for petechiae, purpura, hematoma; monitor for blood in emesis, or sputum; institute bleeding precautions (prevent unnecessary venipuncture; avoid intramuscular [IM] injections; prevent trauma; be gentle with oral care, suctioning; avoid use of a sharp razor); administer prescribed stool softener
Gas exchange (Related to deficient oxygen capacity of the blood secondary to blood loss)Irregular breathing pattern, use of accessory muscles; altered chest excursion; adventitious breath sounds (crackles, rhonchi, wheezes, diminished breath sounds); copious secretions; signs of hypoxia; altered blood gas results; confusion; lethargy; cyanosisMonitor respiratory rate and effort based on assessment of patient condition; assess lung sounds frequently; monitor for secretions, bloody sputum; suction as necessary; use pulse oximetry to monitor oxygen saturation; collaborate with physician to administer oxygen as needed; elevate the head of the bed 30 degrees or higher; monitor IV fluids and avoid aggressive fluid resuscitation; assess level of consciousness; anticipate the need for possible intubation
Tissue perfusion (Related to decreased hemoglobin secondary to bleeding; altered clotting factors)Hypotension; dizziness; cool extremities; pallor; capillary refill greater than 3 sec in fingers and toes; weak pedal pulses; altered level of consciousness; altered sensationMonitor blood pressure; assess for dizziness; assess extremities for skin temperature, color, warmth; assess capillary refill; assess pedal pulses; monitor for numbness, tingling, hyperesthesia, hypoesthesia; monitor and trend PT and INR; administer blood or blood products as ordered; administer vitamin K as ordered; administer IV fluids as ordered; administer fluid bolus as appropriate; administer medication to support blood pressure as ordered; monitor and trend PTT results
Health management (Related to complexity of health-care system; complexity of therapeutic management; knowledge deficit; cultural family health patterns; mistrust of HCP)Inability or failure to recognize or process information toward improving health and preventing illness with associated mental and physical effectsFacilitate collaboration with HCP to develop a plan of care that supports health; ensure patient adheres to recommended medication regime; encourage patient to comply with health-care follow-up appointments

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in evaluating the effectiveness of blood clotting.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s hematopoietic and hepatobiliary systems, especially any bleeding disorders and other symptoms, as well as results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including anticoagulants, aspirin and other salicylates, herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus). Such products should be discontinued by medical direction for the appropriate number of days prior to a surgical procedure. If the patient is receiving anticoagulant therapy, note the time and amount of the last dose.
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture. Fill tube completely. Important note: When multiple specimens are drawn, the blue-top tube should be collected after sterile (i.e., blood culture) tubes. Otherwise, when using a standard vacutainer system, the blue-top tube is the first tube collected. When a butterfly is used and due to the added tubing, an extra red-top tube should be collected before the blue-top tube to ensure complete filling of the blue-top tube.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis. If delays in specimen transport and processing occur, it is important to consult with the testing laboratory. Whole blood specimens are stable at room temperature for up to 24 hr. Specimen stability requirements may also vary if the patient is receiving heparin therapy. Some laboratories require frozen plasma if testing will not be performed within 1 hr of collection. Criteria for rejection of specimens based on collection time may vary among facilities.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.
  • Patient Education

    • Instruct the patient to report severe bruising or bleeding from any areas of the skin or mucous membranes.
    • Inform the patient with prolonged aPTT values of the importance of taking precautions against bruising and bleeding, including the use of a soft-bristle toothbrush, use of an electric razor, avoidance of constipation, avoidance of acetylsalicylic acid and similar products, and avoidance of IM injections.
    • Inform the patient of the importance of periodic laboratory testing while taking an anticoagulant.
    • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP.
    • Answer any questions or address any concerns voiced by the patient or family.
  • Expected Patient Outcomes

    • Knowledge
    • States signs and symptoms of bleeding that should be reported to the HCP
    • States purpose of heparin infusion in relation to medical diagnosis
    • Skills
    • Demonstrates the proficient use of nasal spray and lip balm to prevent cracked mucous membranes and associated bleeding
    • Demonstrates proficiency in the self-examination of skin for bruising and bleeding
    • Attitude
    • Complies with the request to refrain from at-risk behavior that would cause bleeding
    • Complies with the request to refrain from using herbal supplements unless approved by the HCP due to increased bleeding risk

Related Monographs

  • Related tests include antithrombin III, bleeding time, coagulation factors, CBC, CBC platelet count, copper, d-dimer, FDP, plasminogen, protein C, protein S, PT/INR, and vitamin K.
  • Refer to the Hematopoietic and Hepatobiliary systems tables at the end of the book for related tests by body system.
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