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Activated Partial Thromboplastin Time (APTT) Converter
Activated Partial Thromboplastin Time (APTT) is a fundamental coagulation screening test used to evaluate the intrinsic and common pathways of the clotting cascade. It specifically measures the functionality of Factors XII, XI, IX, VIII, X, V, II (Prothrombin), and I (Fibrinogen).[Image of intrinsic and extrinsic coagulation pathways]
Clinically, APTT is the standard method for monitoring Unfractionated Heparin (UFH) therapy. A prolonged APTT may indicate clotting factor deficiencies (such as Hemophilia A or B), the presence of inhibitors (like Lupus Anticoagulant), or disseminated intravascular coagulation (DIC). While the result is universally reported in Seconds, understanding the relationship between raw time and the APTT Ratio (Patient Time / Mean Control Time) is crucial for standardizing heparin therapeutic ranges across different laboratory reagents.
SI / Standard Unit
RecommendedThe universal standard for reporting clotting time.
Other Formats
*Ratio calculation assumes a mean normal control of 30 seconds.
Clinical Context
The reference range for APTT typically falls between 25 and 35 seconds, though this varies significantly depending on the specific activator and phospholipid reagents used by the laboratory.
For patients on Unfractionated Heparin, the target therapeutic range is often 1.5 to 2.5 times the mean control value (approx. 60–80 seconds), although many institutions now transition to Anti-Xa assay monitoring for greater accuracy. Isolated prolongation of APTT with a normal Prothrombin Time (PT) suggests a defect in the intrinsic pathway (e.g., Factor VIII or IX deficiency).
Clinical References
How to Use This Calculator
Follow these steps to get accurate clinical conversions instantly.
Enter Values
Input your laboratory results into the Seconds field. You can use either dot or comma decimals.
Automatic Conversion
The calculator works in real-time. The estimated Ratio (based on a 30s control) will update instantly.
Verify Units
Check the SI Units section for the standard reporting format.
Reset
Use the Clear button to reset all fields before starting a new calculation.
Frequently Asked Questions & Tips
Ratios help standardize results across different labs, especially for monitoring heparin therapy, though reagents vary.
The “Seconds” are absolute. The “Ratio” field assumes a standard control of 30 seconds; your lab’s control may differ.