A patient on heparin therapy is found to have aPTT = 85 sec (control = 30 sec). He is stable and not bleeding. What should be the next step?

Correct option is B

Therapeutic range of aPTT on heparin = 1.5–2.5 × control (≈45–75 sec). An aPTT of 85 is slightly above target but acceptable if no bleeding; hence, therapy can be continued with close monitoring.
Explanation of options: (a) ✘ Protamine is given only in bleeding or very high aPTT. (b) ✔ Correct; continue therapy as patient is stable, just monitor. (c) ✘ Increasing dose will push aPTT dangerously higher. (d) ✘ Switching to warfarin is long-term therapy, not immediate change here.