Medically Reviewed by Dr. Bryan Seigel D.C., P.L.C.
The best way to know you’re in ketosis is to track your ketones, and to do that you need to test them regularly. Your circulating blood ketones are an accurate measurement of the ketones you’re producing and using on any given day, but you have to watch out for a few pieces of confounding data. First, we’re going to talk about how to get the most accurate results from using your blood ketone meter, then we’re going to get into a few details that you should know at the moment of testing. If you’re not sure exactly what ketones are or how they work, jump over here for a review.
How do you get the most accurate measurements of blood ketones?
It’s best to test your ketones at the same time every day, while fasted. Avoid testing first thing in the morning, since cortisol is elevated from the waking-up process (called the dawn effect) and can both raise glucose and lower ketones. Mid-morning or mid-afternoon are ideal times, at least 2 hours after you’ve eaten. Just before a meal is also a great time. In the two hours after a meal, blood glucose and ketones are variable, and many people see a drop in ketones after eating, so you won’t get accurate results this way.
You might be tempted to measure your ketones right after a workout. Unfortunately, this is not a representation of your AVERAGE ketone level through the day. Many people see very low or very high ketones after a workout, and this is an individual reaction based on the type of workout, glucose utilization, and hormonal balance. Just like with a meal, it’s best to wait 2-3 hours to use your blood ketone meter.
Using your blood ketone meter
Since there are several models of blood ketone meter on the market, and they upgrade their meters periodically, this isn’t a guide on using a specific meter. Instead, these are the best practices for using ANY blood ketone meter that will hold true no matter what meter you choose.
Since testing your blood requires breaking the skin, choose a clean environment. Wash and dry your hands, and insert the ketone test strip into the meter. Use your lancet to lightly prick a fingertip, just deeply enough to draw blood. Most lancet devices have settings that allow you to change how much pressure it uses so choose the one that’s just enough to break skin without jabbing deeply (and painfully).
You should see a little drop of blood start to pool on your finger, and you want to wipe this first little drop away as there can be residual glucose in it from breaking the skin which will make your results inaccurate. If a second drop doesn’t start forming, you can gently press on your finger to encourage a larger drop to form.
Touch the ketone strip to the drop of blood and let the strip absorb that drop. It needs very little blood to test, but if there’s too little blood it will give you an error and you’ll have to use a fresh strip. It may take up to 10 seconds to get results. Record your results (or sync your meter with the app, if one is available) and safely discard the strip and the lancet. Pro tip: keep a small cardboard box handy for disposal of lancets and strips. This keeps the needles from poking through a trash bag.