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Bicarbonate Vs. PaCO2 Blood Tests

Discussion in 'Labs' started by haidut, May 24, 2015.

  1. haidut

    haidut Member

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    Hi all,

    I have been reading up on the tests Labcorp offers and how they are performed. It looks like the test for blood CO2 is actually a test for bicarbonate and not a direct measure of CO2. The reason I am asking this question is that several websites suggest that high bicarbonate is associated with alkaline blood (which makes sense of course) and low level are associated with acidic blood. So, if CO2 acidified the blood it would suggest that it is low bicarbonate levels we want, not the other way around. Btw, the drug acetazolamide works by doing two things - increases excretion of bicarbonate through the kidneys (which makes the blood acidic) and also reduced conversion of CO2 into bicarbonate. Also, aspirin in higher doses acidified the blood and has been know to cause low bicarbonate levels and even metabolic acidosis in some people. Here are some links.
    http://labtestsonline.org/understanding ... /tab/test/
    http://en.wikipedia.org/wiki/Acetazolamide
    http://www.medscape.com/viewarticle/442088


    The above links suggest that what we need is to measure PaCO2 and not bicarbonate levels. It also suggests that we want LOW bicarbonate levels as shown on the standard CO2 tests done as part of a metabolic panel. High bicarbonate levels are associated with alkaline blood and cellular state, which is something Peat views as bad.

    And finally this link says that alkalosis is caused by either high blood bicarbonate or low CO2, or combination of both. So, bicarbonate and CO2 in blood do seem to be inversely correlated.
    http://www.healthline.com/health/alkalosis#Causes2

    Am I misreading and/or misunderstanding something?
    Thanks in advance.
     
  2. Dean

    Dean Member

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    So, could this mean that something like magnesium bicarbonate water could be a bad idea? I mean, I've been drinking up to a whole liter of the concentrate here in the last few days to try and keep my magnesium levels up with my high calcium intake. Could I be doing more harm than good taking in the bicarbonate form? I was actually thinking the bicarbonate would be protecting against metabolic acidosis (since I've been also taking small doses of flowers of sulfur twice a day to improve lactose tolerance).

    Do I have it upside down (now there would be a surprise) and the bicarbonate--at least in that amount--could be making me more susceptible to metabolic acidosis?
     
  3. OP
    haidut

    haidut Member

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    Let's wait for others to chime in. Maybe I am wrong, but this link also suggests that high bicarbonate is associated with low CO2 and as such is a possible cause of alkalosis.

    http://www.healthline.com/health/alkalosis#Causes2

    I think ingesting bicarbonate is not the same as bicarbonate in the blood since it will react with stomach acid and release CO2 in the process. It is the bicarbonate in the blood that I am concerned about. If it turns out we want low bicarbonate levels an the common tests for CO2 measure bicarbonate level then many people on the forum showing results with high bicarbonate actually have a problem, while they have been reassured that it is a good sign.
     
  4. Dean

    Dean Member

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    Wasn't there someone on the forum here, who got alkalosis from too much baking soda on top of their high milk consumption? I think I remember Peat had also cautioned about that risk. Wouldn't that seem to indicate that bicarbonate would be alkalinizing? Then again, I'm not a scientist, have never played one on tv, or even slept at a...So I don't know. Maybe it was acidosis that happened to them? Hopefully they will see this thread and clarify.
     
  5. OP
    haidut

    haidut Member

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    It was forum member "j.", who said that he got the dreaded "milk alkali" syndrome.
    http://en.wikipedia.org/wiki/Milk-alkali_syndrome
    It is indeed a type of alkalosis and caused by too much calcium usually combined with other alkalizing agents like sodium bicarbonate. The syndrome causes temporary kidney failure and takes months to recover from. Not pleasant at all.
     
  6. Dean

    Dean Member

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    Yikes!

    How much calcium is too much? What if you are getting 4000-4500 mg through diet and then drinking a liter of mag bi carb water concentrate a day?
     
  7. Suikerbuik

    Suikerbuik Member

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    You are right by saying that HCO3- isn’t giving absolute indictaion of CO2 level, though it is quite reliable in healthy subjects. Usually low HCO3- is a direct sign of low CO2 production, but not telling you the exact situation, for instance, like you said, having high carbonic anhydrase expression you could very well end up having high HCO3- but low CO2.

    However, for HCO3- status venous blood works well. While for paCO2 you need arterial blood and that is usually not being drawn by regular lab workers.

    Indeed, being too alkaline or to acidic isn't good, hence the recommendation for the use of 1 to 1.5g bicarb/day if you're not testing pH.

    Hopefully someone like Blossom could join in, I think she has much more knowlegde on this! :).
     
  8. OP
    haidut

    haidut Member

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    OK thanks. But my questions is also about acidity and Ph. If acetazolamide lowers bicarbonate and increases CO2 (and aspirin does the same) then taking those drugs would skew results right? Also, if lowering bicarbonate is what leads to increased CO2 (since less bicarbonate means less available to "neutralize" CO2) doesn't that suggest we should be aiming for low bicarbonate on blood tests, all other things being equal? If bicarbonate is a rough measure of CO2 production then why is the blood bicarbonate test used to test for alkalosis? IN other words, high bicarbonate is indicative of alkalosis, but if bicarbonate was a measure of CO2 production then it would mean CO2 is also high, so nothing to worry about. Except that's not how physicians interpret the test. Something is amiss here, IMHO.
    Furthermore, what if someone is taking aspirin? How would that show up on their blood test? The link above suggests aspirin would lower bicarbonate, but we know that aspirin also increases CO2. In fact, aspirin lowering bicarbonate is why it should not be taken together with acetazolamide - i.e. together they may cause acidosis. So, if one is lowering bicarbonate with aspirin and acetazolamide then how does one
    Most of the medical websites agree that just measuring bicarbonate is next to useless. They suggest always testing together with pH, PaCO2, and all electrolytes plus phosphorus. With that mind, do you know how electrolyte levels correlate with CO2 levels?
    This is getting so confusing. No wonder Peat does not trust blood tests...They can only be useful when done all together and even then are subject to interpretation. So, the annual exam should test for 200+ biomarkers to be meaningful. I am sure doctor like the sound of that:):
     
  9. sunmountain

    sunmountain Member

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    My recent labs showed CO2 at 31, with 31 being upper limit. I remember feeling surprised that my CO2 was so high when I wasn't feeling well.
     
  10. Blossom

    Blossom Member

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    Here is my understanding FWIW: The body tightly regulates our blood pH between 7.35-7.45. If 'acidic' CO2 gets too high then bicarbonate (HCO3) works to balance it out. An arterial blood gas (ABG) analysis is the most accurate test to see CO2 status via pCo2. The main problem with getting this test as suikerbuik mentioned is that very few people are specially trained to draw blood from an artery and special equipment must be available to analyze the results with in 10 minutes of obtaining a sample. They are primarily drawn in a hospital setting and it's difficult to get a physician to order one unless the person is in critical condition, has severe COPD or possible respiratory failure.

    A venous CO2 sample (bicabonate) will provide a rough estimate because as CO2 rises HCO3 will generally rise as well in most people to compensate. Looking up things like Compensated/Uncompensated Respiratory Acidosis and Alkalosis might provide a more coherent picture of what happens with the blood gasses as CO2 levels change.
     
  11. Blossom

    Blossom Member

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    From reading and listening to Peat I get the impression that his views on pH are a bit different than those of the medical community.

    I do still feel that a venous CO2 can give us a general idea of what's going on but an end tidal CO2 (exhaled breath) might be more practical and accurate if a person has access to the equipment.
     
  12. Blossom

    Blossom Member

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  13. Suikerbuik

    Suikerbuik Member

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    On lab tests yeah.
    Nope, at least not the way I understand it..

    What leads to increased CO2 is lower conversion of CO2 to bicarbonate.

    HCO3- doesn't bind to CO2. CO2 is not acidic by itself, it is so because when combining with water it wil release a proton. Bicarbonate ‘neutralizes protons’ (aspirin – salicylic acid), which result in low bicarbonate and higher CO2, but you need bicarbonate initially.

    Also keep in mind that the whole reaction is reversible, despite this reaction being generally slow, it tells us that says that low bicarbonate will also result in lower CO2 and therefore, again not a good option.

    Along with the blood pH being 7.4, I hold value to having HCO3- being well in range.

    No not in the case of increased carbonic anhydrase activity.
    In theory I’d say resulting in lower serum bicarbonate because of the acidity, perhaps higher intracellular CO2.
    How it correlates? I don’t know, but I’m interested as well..
    Yes the more you make me think about it, the more confused I get!
     
  14. Blossom

    Blossom Member

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    I get the impression from reading Peat that the ICF (intracellular fluid) should ideally be slightly acidic (due to CO2 production from optimal cellular respiration) while the ECF (extracellular fluid) would be slightly more alkaline. I reached this conclusion from Peat's article entitled Altitude and Mortality although he talked a bit about it further in one of his radio interviews. I'm willing to concede that my interpretation may be incorrect.
     
  15. OP
    haidut

    haidut Member

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    Thanks again. I think we are getting somewhere in this discussion. So, in summary I think we can agree on this:

    1. Measuring plasma bicarbonate is a decent measure of plasma CO2 as bicarbonate represents 94%+ of the CO2 reserves in the body. However, this test is only reliable in healthy people and people NOT taking any drugs that can change pH such as aspirin, acetazolamide, etc.
    2. If people are taking such acidifying drugs, then they may have low plasma bicarbonate on blood tests but actually higher plasma (and maybe also intracellular) CO2. So, whenever people report blood tests here we need to be asking if they are taking such drugs.
    3. Ideally, one should have an arterial blood gas work up done but it is rarely done and usually in a hospital setting. So, instead an end tidal CO2 beathing measurement should be done.

    Am I summarizing this correctly?
     
  16. OP
    haidut

    haidut Member

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    Also, since we already started this topic, I wanted to ask a related question. The regular finger oxymeters with pulse claim to measure blood oxygenation. It is commonly used in doctor's offices and in hospitals. Most doctors want to see a reading north of 96% oxygenation to be content that the patient is not hypoxic.
    However, Peat has suggested that we probably need the exact opposite result - i.e. a low reading would indicate that the blood is releasing its oxygen into the tissues due to the high presence of CO2 there. So, according to Peat a high reading on the oxymeter would indicate hypoxia, with a reading of 100% being found in dead organisms. He said that he personally felt best when his oxymeter was showing readings below 90%, which in a regular hospital setting would trigger hypoxia treatment. Also, forum member "iLoveSugar" said he regularly gets readings below 92% and he feels like crap 24x7.
    Peat's explanation certainly makes sense, but I just find it difficult to believe that millions of people would use the device in the exact opposite (and wrong) way and potentially put in danger the lives of millions of patients. Also, I know of several forum members who have sent me their results saying they felt really bad and invariably their oxymeter readings (when they had them done) were 92% and below.
    So, what is the correct answer? What reading do we want to see on the oxymeter - high or low?
    I guess it would come down again to combination of tests, and the oxymeter on its own not really giving much information. But I just wanted to throw this out there as many people use this device as part of their daily routine of measuring progress on Peat's diet. Oxygenation is certainly related to levels of CO2 but it seems we have no realiable home-friendly methods of measuring CO2 and/or tissue oxygenation. Maybe one surrogate test would be applying methylene blue topically and seeing how long before it disappears. However, that presumably only tells us about the local tissue oxygenation, not the entire body. I wonder if one puts several drops spread out throughout the body if that would give a decent approximation. Say one drop on each limb and then several on various sections of the torso. However, that may still show local skin status and not deeper tissue.
    Thoughts?
     
  17. Wilfrid

    Wilfrid Member

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    Ray has made reference to Peter A. stewart's work about acid-base chemistry in one of his answers to a forum member.
    viewtopic.php?t=3285
    You may find the answer to this question if you read the chapter six of Stewart's book ( cf Strong ions plus carbon dioxide ( isolated, intact interstitial fluid) page 87 )
    http://issuu.com/acidbase/docs/htuab

    So, following the Stewart's approach of acid-base chemistry, the arterial blood plasma is considered an aqueous solution exposed to a partial pressure of constant Co2 ( PCo2) containing a mixture of strongly dissociated ions ( Na+, K+, Cl-, lactate....) and weak acids ( albumin and phosphorus).
    For example: according to the ( seemingly obvious) traditional approach, the alkalinizing effect of a sodium bicarbonate perfusion is due do the contribution of the bicarbonate. But according to Stewart, it is not.
    The bicarbonate ion is ultimately only Co2 which is in the form of bicarbonate due to the positive strong ion difference ( SID ) ( one can get more info about it through Wikipedia Peter A Stewart's page or by reading his book ), and, thus, the providing sodium bicarbonate is nothing more than a perfusion of Na+ and Co2. So, it's the Na+ intake which, by increasing the SID, exerts an alkalinizing effect on the plasma. The elevation of plasma bicarbonate which follows the sodium bicarbonate perfusion is therefore the result of an increase SID. If one was able to perfuse only bicarbonate ions to a patient ( without the strong added cation: Na+), we would even have an acidifying effect comparable to that of a single intake of Co2.
    I know that is not the "conventional" view of acid-base chemistry but, at least, it can give more insight on how electrolytes could interacts on the acid-base system.
     
  18. Blossom

    Blossom Member

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    The thing about a pulse oximeter is that you really DO have to have a pulse for it to work. Part of the technology is that it uses an infrared spectrometer to estimate how saturated the hemoglobin is with oxygen as it 'pulses' through the area being checked (finger tip, earlobe). It doesn't tell us if the oxygen is being utilized only if it is being carried on the hemoglobin so that's one draw back. If a person's nailbeds and mucus membranes are nice and pink that's a good indication that the tissue are adequately oxygenated. For the most part they work fine for getting a rough estimate of what's going on but there are a few rare instances such as carbon monoxide poisoning where a false high reading will occur. Smokers will have a higher pulse ox reading during and immediately after smoking because of the CO having a higher affinity to bind to hemoglobin.

    People at higher altitudes will have a lower Sp02 reading simply because there is less oxygen in the air. When the lower readings were discussed I thought Peat was referring to having a lower reading at high altitude as being acceptable.

    From personal experience I had a point or two higher sp02 reading when I took diamox which confirms Peat's stance that raising CO2 helps with oxygenation (my nailbeds were pinker too). The same thing happened with regular bag breathing as Peat has mentioned.

    Even though 96% or higher is often mentioned as an ideal Sp02 level in actuality above 92% in the absence of lung disease and above 88% in the presence of lung disease are typical 'medical' standards.

    Many people with lung disease report feeling better with an Sp02 between 88-92%. Those people are usually breathing off a hypoxic (low oxygen) drive which their bodies have adapted to over time. For the rest of us CO2 levels control our ventilatory drive.
     
  19. OP
    haidut

    haidut Member

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    Thanks to both Blossom and Wilfrid for the answers.
     
  20. narouz

    narouz Member

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    I remember Peat discussing this different way of conceiving of pH in an interview.
    I recall that he referred to the model of the typical home water softener
    by way of explanation.
    Perhaps Ling came into his explanation too...?

    Have to confess I don't have the biological/chemical understanding to really grasp
    what he was talking about.
     
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