Coagulation screen

Coagulation screen is a comprehensive blood test used to assess the blood's ability to clot properly. It is an essential diagnostic tool in the evaluation of bleeding disorders, such as hemophilia and Von Willebrand disease, and in monitoring patients who are on anticoagulant therapy. The coagulation screen encompasses several tests, including the Prothrombin Time (PT), Activated Partial Thromboplastin Time (aPTT), Thrombin Time (TT), and Fibrinogen level assessment.

Overview

The coagulation cascade is a complex process involving multiple factors that lead to the formation of a blood clot. It is divided into three pathways: the intrinsic, extrinsic, and common pathways. The coagulation screen evaluates these pathways to identify abnormalities that can lead to either excessive bleeding or clotting.

Tests Included in Coagulation Screen

• Prothrombin Time (PT): Measures the time it takes for blood to clot. It primarily assesses the extrinsic and common pathways of the coagulation cascade. PT results are often reported as INR (International Normalized Ratio) to standardize the results across different laboratories.
• Activated Partial Thromboplastin Time (aPTT): Evaluates the intrinsic and common pathways. It measures the time it takes for blood to clot after partial thromboplastin and calcium are added.
• Thrombin Time (TT): Assesses the time it takes for thrombin to convert fibrinogen into fibrin, a key step in the clot formation process.
• Fibrinogen Level: Measures the concentration of fibrinogen in the blood, which is a critical protein for clot formation.

Indications

A coagulation screen is indicated in various clinical scenarios, including:

• Evaluation of patients with unexplained bleeding or bruising.
• Preoperative assessment to evaluate bleeding risk.
• Monitoring of anticoagulant therapy effectiveness, such as warfarin.
• Diagnosis of disseminated intravascular coagulation (DIC).
• Investigation of suspected bleeding disorders.

Interpretation of Results

Abnormal results in the coagulation screen can indicate several conditions:

• Prolonged PT may suggest a deficiency in clotting factors associated with the extrinsic and common pathways, liver disease, or the effect of anticoagulant therapy.
• Extended aPTT may indicate a deficiency in factors of the intrinsic and common pathways, the presence of inhibitors like lupus anticoagulant, or the use of heparin.
• Increased TT can be seen in conditions where the conversion of fibrinogen to fibrin is impaired, such as in the presence of heparin or fibrin degradation products.
• Low fibrinogen levels may suggest disseminated intravascular coagulation (DIC), liver disease, or a genetic fibrinogen deficiency.

Conclusion

The coagulation screen is a vital diagnostic tool in the assessment of the blood clotting system. It helps in diagnosing bleeding disorders, monitoring anticoagulant therapy, and evaluating patients' risk of bleeding during surgical procedures. Interpretation of the results requires comprehensive knowledge of the coagulation cascade and should be done in conjunction with clinical findings.