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Hyponatremia and CBC’s

  • 1.  Hyponatremia and CBC’s

    Posted 07-10-2019 18:48
    Our Hematology Lab has two Sysmex XN-1000’s.
    When a specimen is flagged for an elevated MCHC, low patient sodium level needs to be considered.
    We have had a patient with critical sodium’s of less than 120 for the last week.
    Protocol is to dilute the patient 1:5 and rerun for indice results.
    Results are an increase in MCV (78 to 87) and a decrease in MCHC (37.7 to 34).
    How do other labs handle such a situation?
    Sent from my iPhone


  • 2.  RE: Hyponatremia and CBC's

    Posted 07-11-2019 14:58
    Hi,

    If low MCV & high MCHC are indicators of hyponatremia what is the reason behind the dilution protocol?  You have the accurate data for that condition versus what indices might be if not hyponatremic.

    Also going off label means the method elevates from moderate to high complexity requiring research, data crunching, creating a new policy/protocol/procedure, and approval by the CLIA Lab Director.  Is the value of the 'adjusted' indices worth the effort for a customized procedure?

    We don't do this at our facility but I'm very interested to know the reason why your lab does.  Always good to learn from others.

    Dean

    ------------------------------
    Dean Yoshimura
    Laboratory Director
    Waianae Coast Comprehensive Health Center
    Waianae HI
    (808) 697-3648
    ------------------------------



  • 3.  RE: Hyponatremia and CBC's

    Posted 07-11-2019 17:37
    Thank you for your reply. Sometimes we forget about the artifactual effects of hypernatremia and hyponatremia of our hematology analyzers:
    -macrocytic, hypochromic RBC in the hypernatremic patient;
    -microcytic hyperchromic RBC in the hyponatremia patient.
     
    It just takes some extra time to dilute the patient blood, allow the specimen to equilibrate, manually put it the correct results, and comments.
     
    I wondered how other labs handled this. Perhaps a comment per the
    critical sodium result (after the initial CBC) would suffice.
     
    Sincerely,
    Sandy O.


    ------------------------------
    SANDY ODEGAARD
    MEDICAL LAB SCIENTIST
    Vidant Health
    VIRGINIA BEACH VA
    757-376-0518
    ------------------------------



  • 4.  RE: Hyponatremia and CBC's

    Posted 07-12-2019 06:37

         This is something I hadn't heard of and is not in our SOPs; we have a Sysmex.  Apparently, the patient RBCs are diluted by the instrument with an isoosmotic diluent to quantitate for MCV. However, a patient with hyponatremia has an osmotic gradient that allows water to flood the RBCs to establish osmotic equilibrium when the dilution is performed on board.  This does not reflect the true MCV in vivo, hence a dilution is performed before running on the instrument.  We have a few patients in house with hyponatremia, so I'll be looking to see what our Sysmex manual says about this.  That's a great point; we don't want to go "off label" with this practice.  Thanks for the info, everyone!

    Here is a great article I found on this:

    Jens Peter Philipsen & Kirsten Vikkelsø Madsen (2015) Hypo- and hypernatremia results in inaccurate erythrocyte mean corpuscular volume measurement in vitro, when using Sysmex XE 2100,Scandinavian Journal of Clinical and Laboratory Investigation, 75:7, 588-594, DOI: 10.3109/00365513.2015.1062534



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    Elizabeth Fisher
    --
    Vincennes IN
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  • 5.  RE: Hyponatremia and CBC's

    Posted 07-12-2019 06:48
    I think most of us are aware of the problem of MCV (and MCHC) measurement in patients with elevated glucose levels.  In vivo, the cells are of normal size since they equilibrate with the surrounding plasma.  When we put them in an isotonic diluent for measurement in vitro, water flows into the hyperosmotic interior of the cell and the MCV is falsely elevated.  If the cells have more time to equilibrate in vitro to the diluent,, the swelling subsides.

      I found this article
    https://www.ncbi.nlm.nih.gov/pubmed/26305422 in PubMed, that shows that hypernatremia produces the same effect as hyperglycemia.  Hyponatremia produces the opposite effect; cells shrink in vitro. (see image below).  So, it makes sense to use the 1:5 dilution method to correct this problem.  It allows the cells more time to equilibrate in the diluent and the volume measure rises as expected, more accurately reflecting the patient's actual values.  Since the MCHC is a calculated value using the HCT and the HCT is calculated on the instrument from the MCV, errors in MCV affect MCHC.  Get the MCV right and the MCHC corrects as well.

    Thanks for the question.  I wasn't aware of the sodium impacts on these parameters.  I learned something new today. 




    ------------------------------
    [Kathy] [Doig]
    [Leadership Development Committee Chairperson 2018-19]

    [doig@msu.edu]
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  • 6.  RE: Hyponatremia and CBC's

    Posted 07-12-2019 14:57
    We currently perform the same procedure, but only if we have a LOW MCHC and Normal/High MCV.​ We are stopping this process since we have never seen a correction that yielded any clinically significant change.

    ------------------------------
    Ian Wallace
    Hematology Technical Specialist
    Saint Joseph Hospital
    Lakewood CO
    (505) 577-2230
    iwallace0904@gmail.com
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  • 7.  RE: Hyponatremia and CBC's

    Posted 07-12-2019 18:00
    Thank you all for the public and private responses!

    For those with Sysmex analyzers, the flagging for IP Message when MCHC > 36.5 g/dL includes the procedure for severe hyponatremia.

    Knowing that a patient has severe sodium issues, clues the Medical Laboratory Scientist viewing the smear that the analyzer indices could be in error.

    Looking for cold agglutinins (because the MCHC is > 36.5 g/dL from the analyzer printout, when the patient is truly an MCHC of 34) or considering that the patient has microcytic cells (because the analyzer printout is 78, when the patient is 87) could be avoided, if the sodium results are considered.

    Sincerely,
    Sandy O.

    ------------------------------
    SANDY ODEGAARD
    MEDICAL LAB SCIENTIST
    Vidant Health
    VIRGINIA BEACH VA
    757-376-0518
    ------------------------------



  • 8.  RE: Hyponatremia and CBC's

    Posted 07-12-2019 20:35
    Hi Sandy,
    Kathy pointed out that the opposite is true with elevated glucose. Does Sysmex address this also? I plan to read the article she posted.
    Biz

    ---------------------------------
    Elizabeth Fisher
    --
    Vincennes IN
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  • 9.  RE: Hyponatremia and CBC's

    Posted 07-14-2019 15:15
    Edited by Märgen Laratta 07-14-2019 15:18
    Oops, nevermind - just saw that the result is artifactual and introduced by instrument.


  • 10.  RE: Hyponatremia and CBC's

    Posted 07-14-2019 15:57
    In fact, the normal results after the dilution protocol ARE the in vivo results.

    The low MCV is a spurious result - an artifact of diluting the cells in isotonic saline.  Remember the cells in vivo are hypotonic [lower concentration inside than normal] but they are normocytic.  The plasma in vivo is hypotonic too, so the cells are the same size they were before the patient became hyponatremic; that is the cells are normocytic.  

    The problem is that when they are diluted in an isotonic solution, they lose water to the diluent ["water follows solute"] and shrink.  And the other aspect of this is just the speed of the normal sampling and testing.  The shrinkage occurs quickly.  Yet if you let them sit in the diluent, which happens in the time it takes to dilute the sample and retest (but better to let them sit a few minutes), they will equilibrate with the normal isotonic diluent and return to their normocytic in vivo size.

    Also remember, our instruments use MCV to calculate HCT.  Then some use HCT to calculate MCHC.  So the spurious size measurement has a snowball effect on other calculated parameters.  Fix the MCV - the others follow.

    Check out the article in my prior post.   Here is the article link again and the image that shows the problem:
    https://www.ncbi.nlm.nih.gov/pubmed/26305422 


    ------------------------------
    [Kathy] [Doig]
    [Leadership Development Committee Chairperson 2018-20]

    [doig@msu.edu]
    ------------------------------