Normal Activated Clotting Time (ACT)
The normal baseline ACT without anticoagulation is less than 130 seconds (typically 80-130 seconds), though the specific value depends on the measurement device used. 1, 2
Baseline (Non-Anticoagulated) Values
- Normal ACT range: 80-130 seconds across different measurement systems 2, 3
- The upper limit of normal is typically reported as less than 130 seconds (2 minutes 10 seconds) 4
- These values represent patients not receiving any anticoagulation therapy 2, 4
Critical Device-Specific Differences
Different ACT measurement devices yield substantially different values, making it essential to know which device is being used:
- Hemochron devices typically read 30-50 seconds higher than HemoTec devices for the same blood sample 1
- The Hemochron Jr. reads an average of 121 seconds lower than the standard Hemochron 801 on identical samples 5
- The i-STAT system shows a mean difference of 24 ± 101 seconds compared to Hemochron 3
- Both celite and kaolin activators produce different ACT measurements, with celite-activated tests generally yielding different values than kaolin-activated tests 1
Common Pitfall to Avoid
Never apply ACT target ranges from one device to measurements from another device. A "safe" ACT of 480 seconds on a Hemochron 801 would correspond to approximately 360 seconds on a Hemochron Jr., potentially leading to dangerous under-anticoagulation if targets aren't adjusted 5. Always verify which device your institution uses and apply device-specific targets.
Context-Specific Therapeutic Targets
While you asked about "normal" ACT, it's clinically relevant to understand that ACT is primarily used to monitor anticoagulation, where target ranges vary dramatically by clinical context:
During Percutaneous Coronary Intervention (PCI)
- With glycoprotein IIb/IIIa inhibitors: 200-250 seconds 1
- Without glycoprotein IIb/IIIa inhibitors: 250-300 seconds (HemoTec) or 300-350 seconds (Hemochron) 1
During Cardiopulmonary Bypass (CPB)
- Target: ≥480 seconds is the most widely adopted standard for initiating CPB 1
- Historical minimum of >300 seconds was based on early studies showing no circuit clotting above this threshold 1
For Femoral Sheath Removal
During ECMO Support
- Target ACT: 180-220 seconds when ACT monitoring is used (though anti-Xa monitoring is preferred) 1
Measurement Precision Limitations
Both Hemochron and HemoTec devices have suboptimal precision, and the relationship between ACT levels and clinical outcomes (bleeding or thrombosis) remains uncertain 1. The ACT is influenced by multiple factors beyond heparin concentration, including: