This is where the test strips come in...
While they are in no way necessary to the diet, most of us feel more secure with a way to test to know if we are in ketosis at any given time and at what level. The test strips provide a quick and private way to determine that. Simply dip the reagent end of the strip into a urine specimen (collected in a clean cup) and remove immediately. Or alternatively, (the method most of us prefer)
— wet reagent area of the strip by passing through the urine stream. Tap edge of strip to remove excess liquid and check color within 10-15 seconds against the color chart provided on all test strip brands' bottles.
A beige or cream color indicates NO KETOSIS detected. Any shade of pink/purple indicates some level of ketones in the urine. Some people get very hung up on the fact that their friend's/husband's/daughter's etc strip shows a darker color all the time, etc. We are all different. Some of us lose better (and feel better) at lighter or darker levels. You'll soon learn what feels right for you.
What if your sticks don't "turn"?
A negative result does not always mean you're not in ketosis. If you're keeping your carbs below a certain level (different for different people, but the 20 to 40 carbs per day range is a safe bet), you're probably in ketosis. Some people use their ketones more efficiently, and indeed make fewer of them, hence their lack of "spill" into the urine.
Keep in mind, though, that it's possible to keep your actual carb count low (say at around 30 grams), and still side-step ketosis. The culprits? Most often it's from eating foods that contain even a small amount of "High Fructose Corn Syrup" (HFCS), which can cause a strong insulin spike and halt fat burning. HFCS is far more destructive to your health and your weight loss than regular sugar.
You might also be a person who reacts to aspartame intake with an insulin release. The Atkins Center reports up to 25% of people have such a reaction to aspartame (NutraSweet.)
An appreciable amount of trans fats in the diet can also halt weight loss and fat breakdown. Why? Because trans fats are artificial fats that the body fails to recognize as "real", and attempts simply to store them, taking an "I'll deal with it some other time" approach.
My CDC gave me the strip and said to use on my 4th day, which I did. It just confirmed that I was, but I kind of gathered I was yesterday cos I felt OK, no headaches and feeling sick.
Its not something I feel a need to do regularly.