It is hard to tell for sure. Even the strips are not always that clear. One would need to test for blood ketones to know 100%. I am pretty sure that if I go over a number I am out of ketosis and I can often tell by feeling a bit of sugar rush if I eat a high carb item followed by water gain and a weight gain (due to the water). But do not worry about it. It was just one meal. Getting back to normal carb eating will take you back to ketosis fast again