Keto made easy

Chapter 8: Testing for Ketosis: Urine, Blood and Breath

You can test for ketosis three ways: urine strips (cheap, less reliable over time), blood meters (most direct, most expensive per test) and breath meters (no needles, an estimate), and for most people on a weight-loss keto diet, testing is optional.

On this page

What a ketone test measures

When carbohydrate is low, your liver makes three ketone bodies: acetoacetate, beta-hydroxybutyrate (BHB) and acetone. Insulin and glucagon regulate how much gets made (StatPearls, Ketogenesis). For the full process, see What Ketosis Is.

Each test looks for a different one of the three:

So the three tools do not measure the same thing. A low number on one and a high number on another can both be "right."

The three methods compared

Urine strips Blood meter Breath meter
What it reads Acetoacetate in urine BHB in blood Acetone in breath
Cost per test About 6 to 15 cents (his figures, videos 8wOheKcBEd8, xyEZL0HuejI) About $3.50 to $4 a strip (his figures, same videos) Device cost up front; no strips
Needle No Yes, a finger prick No
Gives a number A colour shade Yes, in mmol/L Depends on the device
Best for Beginners checking "yes or no" An actual blood level Repeat checks without strips
Main weakness Fades as you adapt; shade means little Cost adds up fast Indirect; accuracy varies by device

The prices above are what KetoDick quoted in 2017. Check current prices yourself; they change.

Urine strips: cheap and fading

Urine strips are the most common test because they are cheap. KetoDick's figure is that you can test several times a day for under $30 a month (video 8wOheKcBEd8).

Their main limit: acetoacetate in urine is a spill-over, not a design feature. As your body gets better at using ketones, less spills, even if your blood level stays the same (video 8wOheKcBEd8). KetoDick says strips often stop showing positive by month three to six, while the person is still in ketosis (video GojQvo_2GS0).

The shade is not a dial. A dark strip does not mean "more ketosis" in your blood, and it does not by itself mean you are dehydrated. Check the colour of your urine instead (see Hydration).

Full detail: Urine Ketone Strips: How They Work and What the Colours Mean.

Blood meters: the direct reading

A blood ketone meter works like a glucose meter but uses a ketone strip. It reads BHB, the main ketone in your blood, and reports it in millimoles per litre (mmol/L). Some glucose meters can take both kinds of strip (video 8wOheKcBEd8).

The reading is the most direct of the three. The cost is the catch: at a few dollars a strip, daily testing runs to hundreds of dollars a month by KetoDick's arithmetic (video 8wOheKcBEd8).

A blood ketone number also means different things for different people. In someone with diabetes, ketones are a safety marker. A review of ketone monitoring in diabetes covers how levels in nutritional ketosis differ from those in ketoacidosis (Laffel, 1999). See Ketosis vs Ketoacidosis.

Full detail: Blood Ketone Meters: BHB Readings and Ranges.

Breath meters: acetone as a stand-in

Acetone is the smallest ketone body, and some of it leaves through your breath. That is also where "keto breath" comes from. A breath meter estimates how much acetone you are breathing out and uses that as a stand-in for ketosis.

The upside is no needles and no strips. The downside is that it is an indirect estimate, and devices differ. KetoDick lists breath meters with blood meters as the accurate, expensive options, and suggests one for people a couple of years in, when urine strips stop working well (video 8wOheKcBEd8).

Full detail: Breath Ketone Testing: Acetone and Accuracy.

Ketones are not a fat-loss score

A higher ketone reading does not mean you are losing more fat. Ketones tell you your body is making ketones. They do not tell you how much stored body fat you burned that day.

Two metabolic-ward studies show why. When 17 men switched to a ketogenic diet at the same calories, body-fat loss slowed after the switch (Hall et al., 2016). In a second ward study of 19 adults, cutting fat produced more body-fat loss per day than cutting carbohydrate: 89 ± 6 g/day versus 53 ± 6 g/day (Hall et al., 2015).

In longer trials, a healthy low-carb diet and a healthy low-fat diet gave similar weight loss over 12 months (Gardner et al., DIETFITS, 2018). The case for keto in weight loss is mostly about hunger and sticking with it, not about chasing a ketone number. See Chapter 2: How Fat Loss Actually Works.

KetoDick on this: in 2019 he says ketosis is not the goal; low carb is, and ketosis is a perk for energy and hunger. He also says you do not have to be in ketosis all the time to lose weight (video 1JbK1_ClDmY).

Do you need to test at all?

Most people do not need to. Testing is a tool for learning, not a requirement for ketosis.

Testing can help when:

  1. You are new and want proof the diet is working at all.
  2. You suspect hidden carbs in a food you eat often.
  3. Your doctor has asked you to track ketones, for example because you have diabetes.

Testing is mostly noise when:

  1. You already know which foods keep you low carb.
  2. You are months in and strips have gone blank.
  3. Checking numbers makes you anxious or rigid about food.

KetoDick on this: his position changed. In 2017 he called urine strips the one useful item in a "keto kit," good biofeedback for spotting foods that cause problems (video DWI8qQl5BbY), and said any colour, even trace, most of the time is enough (video xyEZL0HuejI). By 2019 he said you do not need a device to check your levels and that it is "probably a waste" of time, and "fun interesting trivia" (auto-caption, video 1JbK1_ClDmY), in his reply to a Men's Health keto article.

Full detail: Do You Need to Test Ketones at All?.

When to involve your doctor

Ketone testing is a medical tool for some people. Talk to your doctor before relying on home ketone readings if you:

The clinical overview of the ketogenic diet also covers monitoring and how nutritional ketosis differs from diabetic ketoacidosis (StatPearls, The Ketogenic Diet). See Who Should Talk to a Doctor Before Starting Keto.

Drill-downs in this chapter

Other guide pages

Blog posts

Videos

Previous: Chapter 7: Electrolytes, Hydration, Vitamins and Keto Flu | Next: Chapter 9: Plateaus and Stalls: Why the Scale Stops and What to Do

Last verified: 2026-10-31