What is the normal range for Activated Clotting Time (ACT)?

Normal Range for Activated Clotting Time (ACT)

The normal range for Activated Clotting Time (ACT) is typically 120-180 seconds in non-anticoagulated patients, with target therapeutic ranges varying by clinical context.

Normal and Therapeutic ACT Ranges by Clinical Setting

Baseline Normal Range

• Non-anticoagulated patients: 120-180 seconds 1
• This represents the baseline clotting time in patients not receiving anticoagulation therapy

Therapeutic Ranges by Clinical Context

Cardiopulmonary Bypass (CPB)

• Target range: 480 seconds or higher 2
• Historical studies initially suggested >300 seconds was adequate 2
• Later research recommended higher targets of 400-480 seconds 2
• Current consensus from the International Society on Thrombosis and Haemostasis (ISTH) recommends ≥480 seconds 2

Extracorporeal Membrane Oxygenation (ECMO)

• Target range: 180-220 seconds 2
• Some centers use lower targets (140-160 seconds) to reduce bleeding risk 2
• Anti-Xa levels of 0.3-0.5 U/mL are preferred for monitoring when available 2

Percutaneous Coronary Intervention (PCI)

• With glycoprotein IIb/IIIa inhibitors: 200-250 seconds 2
• Without glycoprotein IIb/IIIa inhibitors:
  • 250-300 seconds (HemoTec device)
  • 300-350 seconds (Hemochron device) 2

Peripheral Vascular Surgery

• Target range: >180-200 seconds (greater than twice the baseline value) 3
• ACT <200 seconds associated with higher risk of arterial thromboembolic complications 4
• ACT >250 seconds associated with increased bleeding complications 4

Pediatric Cardiac Surgery

• Target range: >480 seconds for neonates, infants, and children 2
• Some programs use >400 seconds 2

Important Considerations in ACT Measurement

Device Variability

• Different ACT devices produce significantly different results:
  • HemoTec and Hemochron devices show poor correlation 2, 5
  • In therapeutic ranges (200-350 seconds), values are not comparable between devices 5
  • HemoTec devices demonstrate better reproducibility (coefficient of variation 2.4% vs 7.2% for Hemochron) 5

Timing Considerations

• ACT values decrease approximately 15% when testing is delayed by 30 minutes 1
• Immediate point-of-care testing is recommended for accurate results 1

Factors Affecting ACT Values

• Hypothermia, hemodilution, and decreased platelet function can prolong ACT 2
• Aprotinin prolongs celite-activated ACT but not kaolin-activated ACT 2
• Different activators (celite vs. kaolin) and detection methods affect measurements 2

Clinical Applications and Monitoring

• For heparin monitoring during procedures, initial ACT should be measured before heparin administration to establish baseline 3
• Supplemental heparin is often needed within 2 hours to maintain therapeutic levels 3
• At procedure conclusion, if ACT >150 seconds, protamine reversal should be considered 3
• Post-procedure ACT should be obtained 15-30 minutes after reversal to detect heparin rebound 3

Remember that ACT measurements should be interpreted in the clinical context, and the specific device used for measurement should be considered when determining appropriate target ranges.