What to do when a high will not come down
A stubborn high often means insulin is not getting in. Why checking ketones comes before another correction, and why stacking corrections leads to a crash.
A high that will not come down is one of the more worrying things to face, and it has a small number of usual explanations. The first move is not another correction; it is to check for ketones, because that changes everything about what to do next.
- A stubborn high often means insulin is not getting in: a failed site, a kinked cannula, or damaged insulin.
- Check ketones when a high will not shift. That single step decides how serious this is.
- Correcting again and again without asking why is how people stack insulin and then crash.
- High with ketones, plus feeling unwell, is the early edge of something serious and follows your sick day plan.
- How you correct, and your ketone thresholds, are set with your team; this page is the shape, not the numbers.
Why a high sometimes will not shift
When a high refuses to come down, the most useful question is not “how much more insulin” but “is my insulin actually getting in”. A surprising amount of the time the answer is no. For pump users, a failed or kinked cannula, a site that has come loose, or an air bubble can quietly stop delivery. For everyone, insulin that has been too hot or frozen can have lost its strength, and injecting into a built-up lump makes absorption erratic.
Other explanations are ordinary. Illness raises your insulin needs, sometimes a lot, so a high during a cold or an infection is the body needing more rather than the insulin failing. Stress and some medications do the same. A big fatty meal keeps glucose up for hours, so a high that will not shift after a takeaway may just be the meal still arriving. And a stubborn high can be a rebound after an overtreated low.
The reason this matters is that the fix is different for each. More insulin helps a genuine shortfall and does nothing for a failed site except set up a crash when the site is fixed and all that insulin suddenly works. So the honest first step is to work out which situation you are in, and the tool for that is ketones.
The check that decides everything
Checking for ketones is the single most important thing to do when a high will not come down, because it tells you whether this is an inconvenience or the start of an emergency. Ketones build when the body cannot get glucose into cells and starts breaking down fat instead, which is exactly what happens when insulin is missing, so a high with ketones is the warning sign that insulin genuinely is not getting where it needs to.
If you have ketone strips, blood or urine, this is what they are for, and pump users especially should have a low threshold for checking because a delivery failure produces ketones faster. Your team will have given you, or can give you, the levels that mean act now, and this is the moment to use your sick day plan, which is the written set of steps agreed in advance for exactly this.
What you do about a high with ketones, including whether and how to correct and by what route, is a clinical plan made with your team, not a number to read off a website. The general shape is: do not ignore it, follow the plan you agreed, and escalate if it is not improving. If you do not have a sick day plan or ketone strips, that is worth sorting before the next time rather than during it.
The stacking trap, and when to get help
The instinct with a stubborn high is to keep correcting, and it is the trap. Rapid insulin takes hours to finish working, so a correction that seems to have done nothing after an hour may simply not have peaked yet, and adding another on top means two doses working at once. That is stacking, and when a failed site is suddenly replaced, or the delayed doses all land together, it produces a hard crash into a hypo, a low that can arrive hours after the corrections that caused it. Give a correction time to work before assuming it has failed, and if it has genuinely failed, suspect the delivery rather than the dose.
For pump users the standard move when a high will not come down and ketones are present is often to stop trusting the pump and use a pen while sorting the site, but exactly how is a plan to agree with your team in advance. The point here is that a failed site is fixed by changing the site, not by asking the pump to try harder.
Get help rather than battling on if the high with ketones is not improving, if you are being sick or cannot keep fluids down, or if you feel genuinely unwell. That is a call to your team or 111. And the emergency signs mean 999 or A and E, not more corrections: deep or fast breathing, breath that smells fruity, severe tummy pain, vomiting, drowsiness or confusion. Those are diabetic ketoacidosis and they do not wait.
What makes a high stubborn
Delivery failure is the one to suspect first when a high will not move despite correcting, because more insulin cannot fix insulin that is not arriving. Illness is the commonest innocent reason and means your needs have risen rather than your insulin failing. And a lump you have been injecting into is an easy-to-miss cause, because those areas feel less and get used more.
How it plays out
Examples, not instructions or doses.
Correction after correction with no effect, because the cannula had kinked. The fix was a new site, not more insulin.
A stubborn high plus ketones and feeling rough. The moment for the sick day plan and getting help, not another go.
Repeated corrections that all landed at once when the site was replaced. Give insulin time, and suspect delivery when it seems to fail.