What is the normal partial thromboplastin time (PTT) range?

• A. 10-20 seconds
• B. 22-35 seconds
• C. 40-60 seconds
• D. 15-25 seconds

Answer: (B)

The normal partial thromboplastin time (PTT) reflects the time it takes for plasma to form a clot via the intrinsic pathway. While the exact number can vary by lab due to reagents and instrumentation, many laboratories define a typical normal range around the low to mid-30s of seconds, with some references as low as about 22 seconds. So a range like 22-35 seconds aligns with what a number of labs consider normal.

Ranges that are much shorter (10-20 seconds or 15-25 seconds) would imply a faster-than-normal clotting time, which isn’t typical for a baseline normal. A much longer range (40-60 seconds) would indicate a prolonged clotting time, suggesting an abnormal intrinsic pathway or effects from anticoagulants like heparin. Since lab reference ranges vary, always check the specific lab’s normal range, but 22-35 seconds is a reasonable standard normal range.