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Disadvantages of Urine Ketone Testing
Something not provided by urine ketone testing? Concrete numbers.
If you like hard data end-points to measure ketosis, urine testing might not be for you. Rather than a concrete number, urine strips give only a semi-quantitative measure of blood ketones, with colors on the strip corresponding to “trace,” “moderate,” and “large” amounts of ketones. Therefore, the test is somewhat subjective.
Many external factors can influence your urine ketone reading, and these could provide a reading higher or lower than what your actual ketone levels might be.
For instance, hydration can influence readings. If you’re under-hydrated, ketones might read high, and vice-versa for someone who’s “over-hydrated.” Certain medications and vitamins (in particular vitamin C) can also skew the results.3
Urine testing may also be a poor way to measure ketosis achieved exogenously. Here’s why.
HVMN Ketone Ester (containing the ketone body BHB) will result in rapid, high ketone levels, equivalent to a multi-day fast or weeks of ketogenic dieting.17 But since we’re testing urine, those rapid increases in blood ketone levels won’t show up in the urine tests.
Most are used for energy, and the pattern of metabolism is quite different from that of endogenous ketone production. Only a small amount of exogenous ketones are excreted.17 It has also been shown that at higher blood ketone levels, urinary ketones no longer correlate with blood BHB.18
As we will discuss later, urinary ketone testing might become less accurate over time, such as if you consistently follow a ketogenic diet for many weeks or months.
Urine Testing and Keto Adaptation
Maybe you’ve been using urine test strips for a significant amount of time to measure the success of your ketogenic diet, and now begin to notice a change in your results, despite your habits staying relatively the same. Don’t blame the strips.
In this case, your metabolism has just changed, something reflected in the strips. When you initially start a low-carbohydrate diet, you’re teaching the body to rely on fat-based fuel sources rather than carbohydrates, which most of us have been using as our primary energy sources for our entire lives.
This necessitates an adaptation period (which can sometimes lead to the “keto flu”), and so for the first few days or weeks of a ketogenic diet, you won’t be great at efficiently producing or utilizing ketones for energy. Despite producing some ketones, you aren’t quite yet a proficient “fat burner.”
This is why ketones will appear in the urine. Since they all aren’t being used, they’re filtered into the urine, rather than being reabsorbed or utilized.
But, after some time on a ketogenic diet, keto adaptation will occur—you’re now more capable of producing and using ketones. At this point, it is possible that a larger amount of ketones are reabsorbed and used for energy, and less will appear in the urine.19 One study indicated that during fasting, the amount of AcAc and BHB increased exponentially as the fast grew longer.19 The same study indicated that there exists no maximal transport rate in the kidney for AcAC during physiological ketosis. That is, our ability to reabsorb ketone bodies might have “no limit.” Furthermore, the increased reabsorption of ketones was shown to minimize the loss of body protein during starvation. Although this study didn’t use people in a keto diet, the same concept might hold true. This is definitely a beneficial adaptation during periods of starvation, since during an actual food shortage, the body would need to conserve more ketone bodies and we might see the same thing in those adhering to a keto diet.
As you become more keto adapted, skeletal muscle actually starts to oxidize fatty acids directly. This then leaves more ketones available for our big juicy brains, and other organs that can’t use fats20,21 This means that someone who is better at using ketones will get a lower result on a urine ketone test than they should, maybe even a negative result. Where blood testing might give a high ketone reading, urine test strips might tell another story.
In summary, over time, urine testing becomes less accurate than blood ketone testing.
Quick Tips for Urine Ketone Testing
If you want to improve the accuracy and reliability of your results, there are a few key tips you should follow if you plan to use urine ketone test strips.
Most obvious is that you should consistently check and stay up-to-date on the expiration date on the urine test strips you’ve purchased. Typically, test strips will expire within six months of opening the bottle. Don’t use your urine test strips if the date on the bottle has passed.
Storage is important too. Make sure that you store test strips with the lid closed tight, and keep the bottle in a cool, dry place. Any excess heat or moisture can influence the strips and the chemicals they contain. Do not store in the refrigerator, and protect them from direct sunlight and heat.
Don’t remove the desiccant in the bottle—that’s the tiny white packet. The desiccant holds something called silica gel, which absorbs and holds water vapor, limiting moisture that could potentially ruin the urine test strips.
During testing, make sure you aren’t overly hydrated, and similarly make sure you aren’t dehydrated, as each could skew the test results. This is why early morning testing makes the most sense. Otherwise, test at the same time of day in order to control for outside influences that might affect urine ketone readings.
Last but not least, keep your hands away from the test strip material. Along with the above tips, this will improve the consistency of your results.
Other Ways to Measure Ketones
Urine testing for ketones isn’t the only way to measure your level of ketosis.