Davis's Lab & Diagnostic Tests
Partial Thromboplastin Time, Activated
General
Core Lab Study
Synonym/Acronym:
aPTT, APTT, PTT.
Rationale
To assist in identification of coagulation disorders and to monitor the effectiveness of therapeutic interventions.
This Core Lab Study is commonly used to evaluate the factors involved in the activation (intrinsic) and common coagulation pathways to help identify factor deficiencies. It is also used therapeutically to monitor the administration of some types of heparin.
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.
| Age | aPTT | ||||||||||||||||||||||||||||||||||||||||
| Neonate–3 mo | 29–56 sec | ||||||||||||||||||||||||||||||||||||||||
| 6 mo | 28–43 sec | ||||||||||||||||||||||||||||||||||||||||
| Adult | 25–35 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. | |||||||||||||||||||||||||||||||||||||||||
| Heparin Type | Heparin Anti-Xa Therapeutic/Prophylactic Range (Chromogenic Method) | ||||||||||||||||||||||||||||||||||||||||
| Age greater than 8 wk–adult | |||||||||||||||||||||||||||||||||||||||||
| UFH (therapeutic range) | 0.3–0.7 international units/mL | ||||||||||||||||||||||||||||||||||||||||
| LMWH (therapeutic range for once daily dosing, sample collected 4–6 hr after subcutaneous injection) | 1–2 international units/mL | ||||||||||||||||||||||||||||||||||||||||
| LMWH (therapeutic range for twice daily dosing, sample collected 4–6 hr after subcutaneous injection) | 0.5–1 international units/mL | ||||||||||||||||||||||||||||||||||||||||
| UFH (prophylactic range) | 0.1–0.4 international units/mL | ||||||||||||||||||||||||||||||||||||||||
| LMWH (prophylactic range) | 0.1–0.3 international units/mL | ||||||||||||||||||||||||||||||||||||||||
| Age less than 8 wk | |||||||||||||||||||||||||||||||||||||||||
| UFH therapeutic range | 0.3–0.7 international units/mL | ||||||||||||||||||||||||||||||||||||||||
| LMWH (therapeutic range, sample collected 4–6 hr after subcutaneous injection) | 0.5–1 international units/mL | ||||||||||||||||||||||||||||||||||||||||
| LMWH (prophylactic range) | 0.1–0.3 international units/mL | ||||||||||||||||||||||||||||||||||||||||
| LMWH = low molecular weight heparin; UFH = unfractionated heparin. Heparin type should be recorded as part of the anti-Xa test request. | |||||||||||||||||||||||||||||||||||||||||
Critical Findings and Potential Interventions
- Greater than 75 to 100 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, easy bruising, 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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