When Is The Best Time To Test Ketones In The Blood?

  • Author: Kara
  • Date: September 20, 2023
  • Time to Read: 4 min.
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Ketone testing can be an important part of a ketogenic diet, helping you track whether you’re in ketosis and how deeply. Blood ketone meters provide the most accurate results, but it’s important to test at optimal times to get meaningful data. Here’s a guide to when and how to test ketones in the blood for best results.

Why Blood Ketone Testing is Better Than Urine

  • Blood testing is more accurate since it measures circulating ketone levels directly, while urine tests show excess ketones you’ve already flushed out 1.
  • Blood levels respond faster than urine to changes in ketone production, giving quicker feedback on impacts of diet, exercise, etc 2.
  • There is no “optimal” blood ketone range for nutritional ketosis – higher isn’t necessarily better. Urine tests only show excess ketones above a threshold, not your actual levels 3.

When to Test Blood Ketones

First thing in the morning, before eating

This will show baseline, fasting ketone levels after hours without food or drink. A reading of 0.5 mmol/L or higher indicates you’ve maintained ketosis overnight 4.

Blood BHB LevelLevel of Ketosis
Less than 0.5 mmol/LNot in ketosis
0.5 – 3.0 mmol/LNutritional ketosis
3.0 – 6.0 mmol/LDeep ketosis
Over 6.0 mmol/LVery deep ketosis – be aware of signs of excessive ketosis

Before and after exercise

Check before and after working out to see if exercise impacts your ketone levels. Some people show a spike after exercise as the body taps into fat stores 5.

2-3 hours after a meal

This will show how different meals affect your ketosis. Testing 2-3 hours after eating allows time for your body to digest and process the food and start fueling with fat again. Large meals, carbs, and protein can all potentially reduce ketones temporarily 6.

Before bed

Checking right before bed shows your ketone levels after a full day of eating and activity. Levels should still be elevated if you’ve maintained ketosis. If not, review what could have knocked you out of ketosis that day.

Anytime you feel symptoms of low ketosis

Test if you notice low energy, cravings, or other signs ketosis may have declined. This can help you link symptoms to your actual ketone levels.

1-2 hours after taking exogenous ketones

If you supplement with exogenous ketones like ketone salts or esters, test 1-2 hours after taking them. This tests for a “exogenous ketone boost” on top of the ketones naturally produced by your body 7.

Testing More Than Once Per Day

For a detailed picture, consider testing ketones 2-3 times at different intervals in a day. For example:

  • on waking after fasting overnight
  • before lunch
  • before dinner
  • before bed

This helps you identify daily patterns in your ketone levels. Just be aware that excessive testing can become obsessive – focus on how you feel overall rather than ketone readings alone.

Factors That Can Impact Ketone Levels

Many variables can raise or lower blood ketone measurements. These include:

  • Carb intake – Eating over 30-50g net carbs per day can reduce ketone levels 8.
  • Protein intake – Eating excessive protein beyond your needs can inhibit ketosis 9.
  • Fat intake – Consuming more fat often boosts ketone production.
  • Hydration – Dehydration can elevate ketones, while drinking water can dilute levels.
  • Exercise – Workouts often raise ketone levels temporarily by burning glycogen and releasing free fatty acids.
  • Time of day – Ketones tend to be lowest in the morning and highest at night.
  • Illness/stress – Sickness and stress can sometimes increase ketone levels.
  • Supplements – Some supplements like MCT oil or exogenous ketones directly raise blood ketone measurements.

The ideal time to test will depend on which of these factors you want to isolate and track. For overall feedback on your baseline ketosis, first thing in the morning is recommended.

Pair Testing With Tracking Symptoms

Don’t rely on ketone testing alone – also track symptoms like energy, mental clarity, cravings, and appetite suppression. Symptoms can often be better indicators of whether you’re truly “in” ketosis. Not everyone feels best with higher ketone levels, either – listen to your body’s response.

Testing Ketones in Urine or Breath

While blood ketone meters are the gold standard, cheaper alternatives include urine test strips and breath analyzers for acetone levels. However, these methods have significant limitations for accuracy and tracking meaningful changes in ketosis. Refer to our guide on the best ketone testing methods for more details.

Wrapping Up: When Is The Best Time To Test Ketones In The Blood?

  • The ideal testing time depends on your goals – e.g. checking baseline ketosis, effects of carbs/protein, or impacts of supplements.
  • Measure at consistent times under similar conditions for comparable results.
  • Track symptoms as well as ketone readings to gauge your level of ketosis.
  • Don’t chase high ketone levels alone – listen to your body’s response to find ideal nutritional ketosis for you.

In summary, blood ketone tracking can be a useful biofeedback tool but not the only metric for ketogenic dieting. Test at smart times and combine readings with symptom tracking to optimize your keto plan.


  1. When Do I Know If I Am In Ketosis?
  2. How Can I Speed Up Ketosis? Tried & Tested Tips
  3. Can Ketosis Be Dangerous?
  4. When Do I Know If I Am In Ketosis?
  5. How Can I Speed Up Ketosis? Tried & Tested Tips
  6. Common Objections to the Keto Diet
  7. What Are The Best Exogenous Ketones?
  8. What are Net Carbs on a Keto Diet?
  9. Keto Basics Quiz: Test Your Knowledge

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