Urine ketones won't be elevated unless blood ketones have been elevated some time in the fairly recent past. But it is possible for blood ketones to be elevated without urine ketones being elevated. A few things, level of hydration can affect ketone levels--drink twice as much water, pee twice as much, and the concentration can go down. Also the kidneys get a big vote on ketone levels, the kidney's are capable of reabsorbing ketones from the bladder so that very little ketones appear in the urine, even at starvation levels of ketosis, one study in the 60's had urine ketones very low even at five weeks or more of starvation in obese subjects given as little as 8.5 grams of glucose a day--urine ketones disappeared, blood ketones remained as high as without the glucose. Also, this tiny amount of glucose spared 12 grams of protein a day in these subjects--about enough to make that 8.5 grams of glucose they were fed. I like the urine strips, they help me stay honest on a ketogenic diet, I try not to read too much into them.