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Comment by lightedman | Hacker News Reader

"The main criticism from outsiders all along has been that blood drawn from a pin-prick just has too much variability for reliable blood testing."

If this is the case, why the hell are we using it for blood sugar level testing in diabetic patients?

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The issue is not that it can't be used for anything, but that what you use it for depends on how much of whatever you're looking for will be present in any given volume of blood.

Sugar is present in sufficient quantities that the variation you get from one pinprick to another isn't going to be a big deal.

Many other things will be present in small enough concentrations that even if it is present in your blood you might not have sufficient quantities for it to be detectable in blood from a single pin-prick.

Going back to the white blood cell count. The gold standard is flow cytometry. If there is an interferent in the sample, or if the cytometer raises any flag, in some labs the backup plan is to do a manual count (100 cells) using whitefield microscopy ... are you really concerned about sampling problems?

I don't see how what you're saying relates to what I wrote.

>If this is the case, why the hell are we using it for blood sugar level testing in diabetic patients?

Because it obviously works for sugar level testing, but not for the kind of tests Theranos claimed to do?

Consider that a glucose molecule is maybe 1.5nm in size, while a red blood cell is 6-8µm and a white blood cell is 12-15µm. Then consider that a capillary is 5-10µm in diameter. The cells actually deform to be able to fit through.

Apart from what the other answer says, notice that diabetics get a pinprick every single day and that only exaggerated values (either low or high) are relevant. And then again, it is a very easy and simple procedure, for glucose, you do not need any fancy laboratory for this single test.

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