Partial Thromboplastin Time, Activated


Core Lab Study




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

Patient Preparation

There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings

(Method: Electromagnetic Mechanical Clot detection) Reference ranges vary with respect to the equipment and reagents used to perform the assay.

Neonate–3 mo29–56 sec
6 mo28–43 sec
Adult25–35 sec
aPTT is prolonged in infants for the first 3 to 6 mo, related to developmental differences in hemostasis and liver maturity, and then decreases to adult levels.

Critical Findings and Potential Interventions

  • Adults and Children: Greater than 70 sec

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid point-of-care testing instrument at the bedside, if available.

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, aPTT levels, unusual ecchymosis, occult blood, severe headache, unusual dizziness, and neurological changes until aPTT is within normal range. Abnormal bleeding associated with standard or unfractionated heparin (UFH) and low molecular weight heparin (LMWH) therapy can be reversed by properly dosed parenteral administration of protamine sulfate.

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