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How to Test Your Blood for Ketones

Instructions and Tips for Home Blood Ketone Testing

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Updated May 14, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

blood ketone meter

Meter testing for ketones in blood

Photo © Andreas Eenfeldt, MD
If part of the goal of your diet is to be in ketosis, you may wonder if you should measure the ketones your body is producing. (I go into some of the pros and cons of that in What is a Ketogenic Diet?) Once you have decided to test your ketones, you have two choices: testing your blood, or testing your urine. Because urine testing is not as accurate, especially as time goes on, more people are turning to home testing of blood ketones.

Note: If you are a diabetic testing for ketone levels to check for ketoacidosis, you will interpret the reading much differently than someone on a ketogenic diet who desires higher levels of ketones. The American Diabetes Association has good information to help you.

What You Need to Test Your Blood For Ketones

A meter that will test blood ketones (the kit includes a lancet pen, a device where all you have to do is push the button and it pokes you to get the blood) - There are two of these on the market in the U.S. that I know of, made by the manufacturers Precision and NovaMax. These meters also test blood glucose, using different test strips. I have looked at the reviews -- people seem happier with the Precision brand, and researchers find it to be the more accurate. The test strips on the NovaMax are less expensive, but also flimsier and there are apparently more error messages, so people report they end up using an extra strip when this happens. Also, when blood ketones are below 1, the NovaMax will sometimes just say "LO", instead of reporting the exact level. Nevertheless, many people opt for the NovaMax and are satisfied.

Test strips - This is the wildly expensive part -- it's the "cheap copier, expensive ink" phenomenon. In the U.S. I have seen prices for the Precision strips up to $6 per strip! If you are diabetic, you may be able to get an insurance company to pay for them. The least expensive way that I have found for people in the U.S. to get them is to order online from Canada, where you can get them for as low as $2 per strip plus shipping. (Some examples are Universal Drugstore, Diabetes Express Pharmacy, and Canada Drugs. I'm not vouching for these particular places; they are just examples.) I have also gotten them from Ebay in the $2.50-$3.00 per strip range.

Here's How To Test Your Blood For Ketones

  1. Load a needle into the lancet pen according to package directions.
  2. Wash your hands with soap, and dry them well.
  3. Remove a test strip from the packaging and insert it into the meter.
  4. Place the lancet pen on the side of one of your fingertips and push the button.
  5. Gentle squeeze your finger to get a drop of blood. The first time, get a good-sized drop, because the last thing you want is to have to throw the strip away because you didn't get enough! After you do it two or three times you'll get a sense of how much blood you need. With the Precision meter, you need a bigger drop of blood than when you are testing blood glucose.
  6. Touch the end of the test strip to the drop of blood until it fills the little opening and the meter registers.
  7. Wait for the meter to give you a reading (just a few seconds).
  8. Record your results.

When to Test

This is mostly up to you. If you have normal blood glucose, your blood ketones may be the highest in the morning after your overnight fast. However, many people report that their ketones rise over the course of the day. If you want to track your blood ketones day-to-day, picking one time of day and sticking with it will give you the best comparison. Some factors besides the overall diet which may cause fluctuations are exercise, and consuming fats with medium-chain triglycerides, such as coconut oil or MCT oil. And, of course, eating something that knocks you out of ketosis.

How to Interpret the Results

If you are new to ketogenic diets, and have a goal of nutritional ketosis (often defined as between .5 and 3 mmol/L), know that it can take 2-4 weeks to get consistently into this range, and it often takes a fair amount of tweaking to figure out what you can and can't eat, even for people who are low-carb veterans. On the other hand, others find it remarkably easy!

Also, if you are measuring ketones in response to diet, it's easy to find a lot of conflicting information about ketone levels, not only on Web sites, but in the directions that come with your ketone meter! This is because the ketone meter was developed in order to alert insulin-dependent diabetics to signs of diabetic ketoacidosis, which is a very dangerous state. You are using it for a different reason entirely, so you can safely ignore that information. (Also, it isn't hard to find "information" that's flat-out wrong, e.g. high ketones are a sign of high blood glucose, or that ketones are caused by protein breakdown, or that they are toxic. But, after all, it's the Internet.)

Tips:

  1. Be sure to get the correct test strips for the correct meter (they are not interchangeable).
  2. Pay attention to expiration dates on the strips!
  3. For more detailed information about nutritional ketosis, I recommend these books by Jeff Volek and Stephen Phinney:
  • The Art and Science of Low Carbohydrate Living


  • The Art and Science of Low Carbohydrate Performance
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    3. Low Carb Diets
    4. Other Popular Diet Plans
    5. Ketogenic Diets
    6. How to Test Your Blood for Ketones at Home

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