Activated Partial Thromboplastin Time
CoagulaçãoÚltima revisão: 7 de abril de 2026. Abordagem de fontes: contexto padrão de interpretação laboratorial, material médico de referência e orientações clínicas ou de saúde pública quando relevantes.
O que é Activated Partial Thromboplastin Time?
Activated partial thromboplastin time (aPTT) is a coagulation test that measures the time it takes for blood to form a clot through the intrinsic and common coagulation pathways. The test evaluates the function of clotting factors XII, XI, IX, VIII, X, V, II (prothrombin), and I (fibrinogen). In the laboratory, a blood sample is mixed with a phospholipid reagent, a contact activator (such as kaolin, silica, or ellagic acid), and calcium chloride, and the time to clot formation is measured in seconds.
The aPTT is one of the most commonly ordered coagulation tests, used both for screening bleeding disorders and for monitoring anticoagulation therapy. It is particularly sensitive to deficiencies in the intrinsic pathway factors (VIII, IX, XI, XII) and is the standard test for monitoring unfractionated heparin therapy. When used in conjunction with the prothrombin time (PT/INR), which evaluates the extrinsic pathway, the two tests together can help localize which part of the coagulation cascade is abnormal, guiding further diagnostic workup for bleeding or clotting disorders.
Por que isso importa
The aPTT is essential for evaluating the body's ability to form blood clots properly. A prolonged aPTT may indicate a bleeding disorder such as hemophilia A (factor VIII deficiency) or hemophilia B (factor IX deficiency), von Willebrand disease, or the presence of an inhibitor like a lupus anticoagulant. In clinical practice, aPTT is critical for monitoring patients on unfractionated heparin therapy to ensure the dose is therapeutic—too little heparin increases clotting risk, while too much increases bleeding risk. The aPTT also serves as a preoperative screening tool to identify unsuspected coagulation abnormalities before surgical procedures.
Faixas de referência normais
| Grupo | Faixa | Unidade |
|---|---|---|
| Adults | 25–35 | seconds |
| Therapeutic heparin range | 60–80 | seconds |
| Newborns | 31–54 | seconds |
As faixas de referência podem variar entre laboratórios. Sempre compare seus resultados com as faixas fornecidas pelo seu local de exame.
O que significam níveis altos de aPTT
Causas comuns
- Hemophilia A (factor VIII deficiency) or B (factor IX deficiency)
- von Willebrand disease
- Unfractionated heparin therapy
- Lupus anticoagulant (antiphospholipid syndrome)
- Disseminated intravascular coagulation (DIC)
- Liver disease (impaired clotting factor production)
- Vitamin K deficiency (affects common pathway factors)
- Factor XI or XII deficiency
- Specific factor inhibitors (antibodies)
Possíveis sintomas
- Easy bruising
- Prolonged bleeding from cuts or dental procedures
- Spontaneous nosebleeds (epistaxis)
- Heavy menstrual bleeding
- Joint bleeding (hemarthrosis)—classic in hemophilia
- Blood in urine or stool
- Excessive bleeding after surgery or trauma
O que fazer: A prolonged aPTT requires further investigation with a mixing study—mixing the patient's plasma with normal plasma to determine if the prolongation corrects (suggesting factor deficiency) or persists (suggesting an inhibitor). Based on results, specific factor levels, von Willebrand factor testing, or lupus anticoagulant testing may be ordered. If on heparin, the dose may need adjustment. Severe bleeding may require factor replacement, fresh frozen plasma, or cryoprecipitate.
O que significam níveis baixos de aPTT
Causas comuns
- Extensive cancer (increased procoagulant activity)
- Acute phase response (increased factor VIII as an acute phase reactant)
- Early disseminated intravascular coagulation
- Elevated factor VIII levels
- Technical or sample issues
Possíveis sintomas
- Usually no direct symptoms from shortened aPTT
- May be associated with increased thrombotic risk in some contexts
O que fazer: A shortened aPTT is less commonly clinically significant but may indicate a hypercoagulable state. Evaluate for thrombotic risk factors, particularly if the patient has a history of blood clots. Check factor VIII levels, as elevated factor VIII is both an acute phase reactant and an independent thrombotic risk factor. Clinical correlation is essential.
Quando o exame de aPTT é recomendado?
- As a preoperative coagulation screening test
- When a bleeding disorder is suspected
- To monitor unfractionated heparin therapy
- When evaluating unexplained bruising or prolonged bleeding
- As part of a DIC workup
- When lupus anticoagulant or antiphospholipid syndrome is suspected
Perguntas frequentes
Biomarcadores relacionados
Referências e abordagem de revisão
As páginas do glossário de biomarcadores são explicações educativas e devem ser interpretadas junto com as faixas de referência e observações fornecidas pelo seu laboratório e pelo seu médico. Para conhecer nossos padrões editoriais e processo de revisão, veja nossa Política editorial e a nossa revisão de conteúdo.
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Enviar resultados de exames →Aviso médico: Estas informações são apenas educativas e não substituem orientação, diagnóstico ou tratamento médico profissional. As faixas de referência podem variar entre laboratórios. Sempre converse com seu profissional de saúde sobre a interpretação dos seus resultados específicos.