Issues Measuring Plasma Lactate and Pyruvate

I saw a story on the national news about looking for elevated lactate measurements as a way to predict pre-term labor (http://lifestyle.in.msn.com/health/article.aspx?cp-documentid=1719305). I don't know anything about the mechanisms having to do with this, but it sounded like dealing with it might have something to do with modifying the baby's respiratory rate with glucocorticoids? That's what the doctor was saying on the news story, on CBS, I think. I don't feel like getting the article right now, but maybe I will later. I wonder if there are issues with measuring the lactate in this case (or if the lactate/pyruvate ratio might be more sensitive and useful to monitor). An elevation in lactate above a level that's normal for an individual or that's "average" would probably imply an elevation in the lactate to pyruvate ratio, but it wouldn't necessarily. I just mean that, if they're developing this test to monitor lactate levels outside of the blood, why not also measure the pyruvate concentration. The lactate/pyruvate ratio might be elevated early on, subtly, before the lactate level is overtly elevated, and this subtle elevation could conceivably give doctors more time to deal with the potential problem, prepare the baby for preterm delivery (as the doctor was talking about, vis-a-vis the baby's lungs).

There are problems with measuring lactate levels in venous blood (the researchers in this study weren't doing that) to detect mitochondrial disorders. The tourniquet that they use to cut off the blood flow to the arm can apparently spuriously elevate the plasma lactate level in the venous blood, because the cells in the hand and fingers can start increasing glycolysis to compensate for the decrease in oxygen delivery for oxidative phosporylation (mitochondrial ATP production). Here's an article that discusses some of those issues. The measurement of pyruvate can be changed by the way the person handles the blood sample. It has to be treated within 30 minutes, etc. There are many, many issues with blood tests and interpreting them, and any one blood test, without the proper interpretation in the individual context of a person's medical history, can lend a false objectivity to a diagnosis or lack of a clear diagnosis. Here's the article on challenges in diagnosing mitochondrial disorders:

http://www.ncbi.nlm.nih.gov/pubmed/18243024

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