Urine Strips, Blood Meters or Breath: Three Ways to Test for Ketosis
In this video
A four-minute comparison of the three common ketone tests, with what each one costs and what it can and can't tell you.
- [0:00] Blood and breath meters are the most accurate and the most expensive. Some glucose meters also take ketone strips.
- [0:30] Blood ketone strips ran about $3.50 a test where I'd seen them in 2017. Daily testing means hundreds of dollars a month.
- [1:00] Urine strips ran about 7 to 15 cents each. They detect acetoacetate, which I described as a "spill" into urine, not something that's there by design.
- [1:30] The more fat adapted you get, the less spills, even at the same level of ketosis.
- [2:00] So strip darkness reflects your urine, not your blood. A positive strip still tells you ketosis is happening.
- [2:30] A dark strip can come from dehydration, but it doesn't prove it. I said a healthy person with healthy kidneys can't reach a dangerous ketone level from diet alone.
- [3:00] Judge water by urine colour, not by the strip. Dark strips in weeks two and three are normal transition spill.
- [3:30] After a couple of years, urine strips stop working well; a breath or blood meter is the option if you have the money. None of it is required.
- [4:00] Where testing earns its keep: you think you're doing everything right and suspect hidden carbs.
The claim worth unpacking: what a strip actually measures
The physiology here is solid ground. Your liver makes three ketone bodies, acetoacetate, beta-hydroxybutyrate (BHB) and acetone, and insulin and glucagon regulate how much (StatPearls, Biochemistry, Ketogenesis). Different tests look for different ones. The video's point that a urine strip reads acetoacetate and a blood meter reads something else is the reason the two disagree.
The other piece is that your body gets better at using ketones as fuel. The classic study is Owen et al., 1967: after weeks of fasting, BHB and acetoacetate replaced glucose as the brain's main fuel. Whatever you use, you don't pass in urine. That fits the "less spill as you adapt" explanation, though no study on the evidence pages measures strip colour over months of keto directly.
On "dangerous" levels, the reviews draw a line between nutritional ketosis and ketoacidosis. Laffel, 1999 covers ketone levels in each and how blood and urine monitoring is used in diabetes. The StatPearls ketogenic diet overview also explains how nutritional ketosis differs from diabetic ketoacidosis. Read my "healthy kidneys, diet alone" line with both conditions attached. It was never meant for someone with diabetes or kidney disease.
Who should treat ketone readings as a doctor conversation
If you have type 1 diabetes, type 2 diabetes on medication, or kidney disease, a ketone number means something different. I deferred on kidneys and type 2 diabetes in the dark-strip video too (video GojQvo_2GS0). Ask your doctor what level should make you call, before you start, not after a strip turns purple.
The same goes for pregnancy. Don't use a forum thread to interpret ketones while pregnant.
Then vs now
This is one of the clearest places my position moved.
- 2017: urine strips were my favourite keto item and good biofeedback (videos DWI8qQl5BbY, 8wOheKcBEd8).
- 2019: about the advice to check your levels with a device, my answer was no, you don't need a monitor, it's probably a waste of time and money (video 1JbK1_ClDmY).
Both are in the transcripts, and both have a point. Early on, a cheap strip is reassurance that you've actually cut carbs. Later on, it fades for the reasons above, and a meter costs real money to tell you something your hunger and the scale trend already say.
I'd frame it now as a beginner's tool with an expiry date. Use strips in the first weeks if they help you learn. Then put them away, and only bring out a blood meter if you're stuck and want to rule out hidden carbs.
The line that holds up
"A dark strip does not mean that you're dehydrated" (from the video). People still post dark strips and get told to drink more water. Look at your urine colour instead: pale is fine, completely clear may mean you're overdoing water. There's more on that in urine colour and hydration.
The line to update is the prices. Those were my 2017 figures, and they will have changed.
Key points
- Blood and breath meters are more accurate and cost more; urine strips are cheap and get less useful the longer you're on keto.
- Urine strips detect acetoacetate in urine. Darkness tracks your urine, not your blood level.
- Fat-adapted people use more ketones as fuel, so less shows on a strip (Owen 1967 for the fuel shift).
- A dark strip is not proof of dehydration; check urine colour.
- Nutritional ketosis and ketoacidosis are different states (Laffel 1999). Diabetes, kidney disease or pregnancy: ask your doctor first.
- By 2019 I said you don't need a monitor at all (video 1JbK1_ClDmY).
Related
- Guide: testing ketosis · urine strips · blood meters · breath · do you need to test? · ketosis vs ketoacidosis · hydration · who should talk to a doctor
- Blog: are dark ketone strips dangerous? · strips not changing colour · optimal ketone level · does ketosis mean burning fat?
- Videos: dark test strips · the Men's Health rebuttal · the keto "kit"