Now I’m not a chemist or anything but I’m pretty sure blood glucose meters work via interaction of the blood with glucose oxidase enzymes and then when that reaction occurs (with a variety of other ions and stuff there to help) that is converted to an electric current that can be quantified by the meter. I’m not sure but I think the blood ketone meters probably work similarly with a different enzyme. Assuming they do both work via electrochemistry it would likely be pretty tricky to design a system where you have both sets of reactions occurring on the same strip and you get separate, accurate numbers for both.
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IRC some of the older meters used photochemical reactions, like traditional pee strips and like the swimming pool testers you find in professional swimming pool shops, however so far as I am aware it is as @glizabetes says above; all the current ones are electrochemical. The photochemical test strips test multiple things, but even then the values are read sequentially; think of a six way pool test strip, you read one swatch at a time, but if you and five other guys get together you can read them all at once.
Measuring two things electrochemically requires two cells because a single cell can only generate a single voltage+current. It’s possible to have multiple cells; after all we are familiar with batteries that, internally, have multiple cells each generating separate voltages. The problem is it really is just sticking two test kits back to back and having two test strips; take a close look at the battery in your car, it really is just six cells stuck together and the various rechargeable batteries for power tools etc are even more obviously so when you take them apart.
Multiple cells make for individual test strips that fail more often than having each cell on a single strip and, worse, the meters themselves have duplicated circuitry that costs at least twice as much. The big deal from our point of view, however, is that two cells need twice as much blood and that will make the “insufficient blood” failure happen way more than twice as often.
The Precision Xtra has one test port and, presumably, one internal set of measurement circuitry that takes two different types of test strip. The test port takes blood or ketone test strips or the data download cable (not supplied 
) . That’s a nice piece of cost engineering; the test port has the electromechanical contacts to the strips/data port and these are the mechanical part that is most subject to wear, so most expensive to engineer. The ketone test seems to take a little longer than the glucose test to complete and both seem to need a little more blood than the Contour USB, but that may just be because they suck it up more slowly.
John Bowler
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