What does a partial thromboplastin time (PTT) of 26 seconds indicate?

PTT of 26 Seconds: Normal Result

A PTT of 26 seconds is within the normal reference range and indicates normal intrinsic coagulation pathway function. 1

Understanding the Normal Range

• The normal range for aPTT using standard reagents (such as Dade Actin FS) is 27 to 35 seconds 1
• A PTT of 26 seconds falls just at or slightly below the lower limit of this reference range, which is still considered normal 1
• Normal PTT values can vary slightly between laboratories depending on the specific reagent and methodology used 2

Clinical Significance

A PTT of 26 seconds indicates:

• Normal function of the intrinsic coagulation pathway (factors XII, XI, IX, VIII, prekallikrein, and high-molecular-weight kininogen) 2
• No evidence of heparin effect - therapeutic heparin anticoagulation requires aPTT values of 60-85 seconds (1.5-2.5 times control) 1
• No lupus anticoagulant or factor deficiencies that would prolong the PTT 3, 2

Important Caveats About Low-Normal PTT Values

While 26 seconds is technically normal, abnormally fast PTTs (defined as <23 seconds) have been associated with increased risk of thrombosis, bleeding, and mortality 4. However, your value of 26 seconds does not fall into this concerning category.

Key considerations:

• PTT values <23 seconds are associated with significantly increased hazards of death (P<0.001), thrombotic events (P<0.001), and bleeding (P<0.006) 4
• Fast normal PTTs (23-25 seconds) show intermediate risk between abnormally fast and mid-range normal values 4
• A PTT of 26 seconds represents a low-normal value without the concerning associations of truly shortened PTT 4

When PTT Monitoring Matters

This normal PTT is relevant in specific clinical contexts:

• Not therapeutic for heparin monitoring - if the patient is on unfractionated heparin, this PTT indicates subtherapeutic anticoagulation, which carries a 10-15 fold increased risk of recurrent thromboembolism 1
• Adequate for preoperative screening - rules out clinically significant factor deficiencies (VIII, IX, XI) that would increase bleeding risk 2
• Not indicative of antiphospholipid syndrome - lupus anticoagulant would prolong, not normalize, the PTT 3, 2

Sample Stability Considerations

If this result seems unexpected, consider preanalytical factors:

• Samples stored at room temperature deteriorate within 12 hours for PTT testing 5
• Refrigerated samples for APTT are unstable after 12 hours (showing >10% change from baseline) 5
• Frozen samples remain stable for PTT testing up to 36 hours 5