An important aspect of the Ketogenic Diet is knowing how high your ketone levels are. There are three types of Ketones; beta-hydroxybutyrate (BOHB) which is measured in the blood, acetoacetate (AcAc) which is typically measured in the urine, and acetone which is typically measured in the breath. The easiest and cheapest technique is to measure AcAc in the urine using a test strip. However, this approach is too inaccurate to be useful. Measuring BOHB in the blood is now practical at home using a similar technique to measuring blood glucose, but is far more expensive. Measuring Acetone in the breath is emerging. Currently, only blood measurement of BOHB is viable, though urine dipsticks are still required to test for kidney stones.
1 Measuring beta-hydroxybutyrate (BOHB)
BOHB is measured in the blood using a small meter similar to a Blood Glucose Meter. A test strip is placed in the meter and a drop of blood is added. After a few seconds, the meter will indicate the level of Ketones. There are two meters on the market in the US, the Nova Max and the Precision Xtra.
- The ketone test strips for Nova Max are cheaper (around $27 for 10 strips), but less accurate and there tend to be a high number of 'bad' test strips.
- The ketone test strips for the Precision Xtra are far more expensive (around $58 for 10 strips), but better quality.
- The best option I've found is to order the Precision Xtra strips from Canada for $20 for 10 strips. I've ordered from the Ketone Strips from Universal Drugstore many times and I've been pleased with their service. It takes a couple of weeks for delivery, and shipping is $7.
- You have to draw a drop of blood for this testing, and I'd recommend the Owen Mumford Advanced Lancing Device for $9. It's not much less painful than other lancing devices, but every bit helps. I also use the narrow (33) gauge BD Ultra-Fine Lancets.
2 Measuring Acetoacetate (AcAc)
AcAc is typically measured in the urine using a test strip, such as the Multistix or the cheaper Phinex Multistix equivalent. These strips check for 10 different things in addition to AcAc, including trace blood, hydration status and urine acidity. (It's important to test for trace blood in your urine if you're on the ketogenic diet to detect Kidney Stones early.) The test strips are cheap, costing around $0.20 each.
3 Measuring Acetone
Acetone can be measured in the breath, which would overcome many of the problems seen with urine AcAc measurement. However, there would still be some delay between changes in the AcAc level and the levels of Acetone, as well as differing levels of AcAc and BOHB. However, the simplicity of this approach and possibly the lower cost could be a huge advantage. The first device I've come across is the Ketonix which is reasonably priced at around $110, but only has a simplistic high/medium/low scale and I've read reports of reproducibility errors (repeated tests giving different values.)
4 My Results
I measured my blood BOHB, urine AcAc (using (KetoAnalysis), and my blood glucose. The charts below show the relationship between the values, with the regression line in blue and the 95% confidence intervals shaded. As you can see, for my readings there is better correlation between blood glucose and blood BOHB than there is to urine AcAc. I tried adjusting for hydration using the Urine Specific Gravity values from the test strips, but this made little difference to the correlation. Multiple regression of blood glucose and urine AcAc to blood BOHB did improve the model to r2=0.73.
5 Problems with Measuring Urine Ketones
In the past the only viable method of measuring Ketones was to use a Urine dipstick, but this is too inaccurate to be useful.
- Urine dipsticks require you to match the color of the test strip against reference patches, so it is not particularly precise. Using image analysis (KetoAnalysis) can help somewhat. (The test strips use a nitroprusside reagent which changes color from pink to maroon. The addition of hydrogen peroxide does not improve the ability of the urine tests to detect BOHB.)
- Worse, there is evidence that the values read from urine dipsticks overestimate the level of ketones in the urine. A study that compared the values from Ketostix with an enzymatic test found the formula "urinary acetoacetate = 0.40(dipstick value) + 0.15" would help correct the overestimation.
- To compound matters further, urine levels do not reflect blood levels of AcAc very well.
- High level of hydration will dilute urine ketone levels.
- Kidney function can change the urine levels as the kidney will reabsorb AcAc. With starvation ketosis, the kidneys increase the reabsorption over time, with one study showing a progression of AcAc reabsorption from 47 (+/-10) mumoles/min on day 3 to 106 (+/-15) on day 10, 89 (+/-10) on day 17 and 96 (+/-10) on day 24. Most studies demonstrate no maximum reabsorption rate.
- There is also a time delay if the blood levels are changing, this will not be reflected in the urine levels immediately.
- A study indicated that the level of urine AcAc and blood AcAc vary in a non-linear manner, following the equation "y = 0.3x0.6 + 0.07" (after correction), but r2 was only 0.59 .
- Further problems arise because the levels of AcAc can be quite different to BOHB levels, as shown below. A study of children using the Ketogenic Diet for epilepsy showed that when blood BOHB levels are over 2 mmol/l, urine AcAc dipsticks indicate levels of 80-160 mmol/l.
- Finally, false positives can occur for a number of reasons.
- Pigmented urine (trace level only).
- Vitamin C.
- Low urine pH (acidic).
- Increased urine specific gravity.
- Phenolphthalein (a laxative used in many preparations under various trade names).
- The amino acid L-dopa.
- Drugs, including
- Fever or burns.
6 See Also
- The classifications and types of Low Carbohydrate Diet.
- An introduction to the Ketogenic Diet.
- My experiences with ultrarunning on the Ketogenic Diet
- How the Ketogenic Diet can be used for the treatment and management of disease.
- Health Risks of the Ketogenic Diet
- The time frame and changes that occur with Ketoadaptation
- What are Ketones
- How to measure Ketones
- What ketone levels to aim for
- The pros and cons of the Ketogenic Diet for athletes
- The Types of Ketogenic Diet
- My Ketogenic Recipes
- Non-Ketogenic Low Carbohydrate Diets
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- http://sensorhealth.com/UrineStripFalsePositive-NegativeCauses.pdf Urine Strip False Positive-Negative Causes
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