Great question! The answer really depends on what you are using the keto diet for! If your goal is weight loss or and increase in your exercise performance, you’ll want to be above .05 mmol/l or trace. If you’re looking to increase your mental clarity or a boost in your mental performance, you’ll want to be between 1.5 mmol/l and 3 mmol/l. Anything higher is really for therapeutic purposes if directed by a doctor.
The problem with the test strips is that you can’t depend on them to be reliable. You can be keeping strictly to less than 20 grams of Carbs and if you are drinking as much water as you should you will barely register “trace” on the sticks. On the other side of that you can barely be in ketosis and if you are dehydrated the test strip can show “large” amount of ketones. Unfortunately it’s not quite as cut and dry as what the test strips are telling you and the only accurate way is checking your blood levels.
Using urine to test your ketosis has its benefits and drawbacks. Because it’s not a closed system, like your blood, outside factors can influence it. Being dehydrated, or overly hydrated will effect the results. The time of day you are testing will also make a difference. So yes, it can be inaccurate.
On the plus side, urine tests are less expensive than the other testing methods, so you can feel free to test regularly. I recommend urine strips for those starting the keto diet, but not for long term.
Blood testing is more accurate, but can get pricey, fast. Once you have developed a routine, and worked the keto diet into your everyday lifestyle, you may want to look into purchasing a blood test kit and strips. By this time, you should have a routine of when you are testing, and know your body’s response to ketosis.