There’s a list to work from rather than a judgment call, which is the right way round for anyone who has to decide this at nine in the evening.
Changes around the wound: worsening redness; more pain; swelling; bleeding; a wound that is larger or deeper; a wound that looks dried out or dark.
Changes in drainage: drainage that is increasing; drainage that is not decreasing after 3 to 5 days; drainage that becomes thick, tan, yellow, green or smells bad. Drainage that is yellowish or cloudy is also on the list for several wound types.
Signs away from the wound: fever or chills. For diabetic foot ulcers, add increased firmness around the wound, and contact a provider if the ulcer is very white, blue, or black. For pressure sores, watch for pus, a foul odor, redness and tenderness around the sore, skin close to the sore that is warm or swollen, and fever. Contact the provider right away if blisters or an open sore develop.
These call for contacting the provider right away: redness, increased pain, or yellow or green pus, or excessive clear fluid around the injury; black edges around the injury; bleeding that will not stop after 10 minutes of direct pressure; pain at the wound that will not go away even after taking pain medicine; and a wound that has come open or stitches or staples that have come out too soon.
Temperature figures differ by wound type and should not be carried across. For a closed surgical wound, the figure is above 100°F (37.7°C) for more than 4 hours. For a surgical wound managed open, 100.5°F (38°C) or higher. For wet-to-dry dressings, 100.5°F (38°C) or higher for more than 4 hours. Use the figure from the instructions for that wound.
One thing worth saying to caregivers plainly: none of these lists requires you to be certain. They describe what to report, not thresholds you have to prove. A clinic would far rather field a call about a wound that turns out to be fine.