Letting Go of the Rule of 3 CAMLT 2018 HANDOUT · 2018-09-29 · Microsoft PowerPoint - Letting Go...

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CAMLT Meeting September 29, 2018

Letting Go Of The Rules of 3…

And How Not To Let The MCHC Rule Your Life

OBJECTIVES

1) Discuss the history of the Rules of Three and their original purpose in hematology testing.

2) Explain the evolution of the RBC Indices and how they are used as indicators of abnormal or problem samples.

3) Apply your knowledge of the RBC Indices to troubleshoot real life case examples.

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Rules of Three

• What are they

• Where they came from

• Why they need to go away


Rules of Three

• HGB X 3 = HCT +/- 3%

• RBC x 3.3 = HGB +/- 1.5 gm/dl

• RBC X 9 = HCT +/- 3%


Actually There Is A Fourth Rule

• This only works when the cells are normal

• Like normal size and normal hemoglobin content

THEN WHY ARE WE STILL DOING THIS???


A Brief History Lesson


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A Long Time Ago…

• Methods were primitive


And Then Laboratory Science Advanced

• TO THESE INSTRUMENTS OF TORTURE

Sahli Adams Hemometer


A Young Man Named Wintrobe

• Invented a reliable and reproducible Hematocrit

• Derived the relationship of RBC, HGB and HCT

• Called them Indices


What Wintrobe’s Indices Did

• Provided information about RBC size, HGB concentration and HGB weight

• Primarily used to categorize Anemias• Over 4 million people in US are affected• 50% are under the age of 45• Over 400 types of anemias have been identified


Wintrobe’s Indices

• MCV = (HCT/RBC) x 10

• MCH = (HGB/RBC) x 10

• MCHC = (HGB/HCT) x 100


Original Wintrobe Reference Ranges


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What the Indices Told Us

• RBCs were normal, big, or small

• Red cell HGB content was normal, increased or decreased


Who Could Do This Math In Their Head?

• MCV = HCT/RBC x 10

• MCH = HGB/RBC x 10

• MCHC = HGB/HCT x 100


So We Made The Math Easier

• MCV = HCT/RBC x 10• RBC X 9 = HCT +/- 3%

• MCH = HGB/RBC x 10• RBC X 3.3 = HGB +/- 1.5 gm/dl

• MCHC = HGB/HCT x 100• HGB X 3 = HCT +/- 3%


And Even Easier……AKA The Rules Of Three

• RBC x 3 = HGB

• HGB x 3 = HCT


Making Sense Of The Rules Of Three

• The rules told you if your RBC, HGB, HCT results made sense

• You still needed to calculate the indices unless you had one of these…..


Now We Get The Indices On Our Analyzers


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Regardless Of What Instrument You Use….You Know When You Have A Problem


Classic Impedance Had Its Limitations

• MCHC – locked into a narrow, normal range

• MCHC became an instrument function indicator rather than a clinical parameter

(adding sheath flow to classic impedance fixed this)

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Classic Impedance vs Impedance With Sheath Flow

• IT’S ALL ABOUT DIFFERENCES…..• Fluidics • Natural deformability of RBC• Hypertonic vs Isotonic diluent


Classic Impedance Sheath Flow Impedance


Natural Deformability Of Red Blood Cells: Normal Cells Do This


But…When The Red Cells Are Not Normal, Hypochromic Cells ‘Over Deform’ In Classic Impedance

CELLS ZIP THROUGH TOO FAST SIZE IS UNDERESTIMATED HCT ARTIFICIALLY DECREASED MCHC ARTIFICIALLY INCREASED

CONTROLED BY SHEATH FLOW ACCURATELY SIZED ACCURATE HCT AND MCHC

Copyright© 2018 Sysmex America, Inc. All rights reserved.

• Sheath Flow Controls This

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When The Red Cells Are Not Normal, Hyperchromic Cells Don’t Deform Enough In Classic Impedance

CELLS MOVE THROUGH TOO SLOW SIZE IS OVER ESTIMATED HCT ARTIFICIALLY INCREASED MCHC ARTIFICIALLY DECREASED

CONTROLED BY SHEATH FLOW ACCURATELY SIZED ACCURATE HCT AND MCHC

Copyright© 2018 Sysmex America, Inc. All rights reserved.

• Sheath Flow Controls This

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We Have Better Technology But….

• We are still stuck on the idea that an MCHC cannot be higher than 36.

• That the HCT has to be 3 X the HGB.

• If the reference range encompasses 95% of the normal people

……..where are the other 5% ?


MCHC Value Of Normal Donors

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What We Need To Do

• Stop doing the Rules of 3 in our head – they don’t work if the red cells are abnormal

• We have the red cell indices – use them

• If the indices are out of whack – investigate

• Accept the fact that an MCHC of 37 is a possibility


When Is It Acceptable

• Low MCV, Low MCHC – can indicate there are microcytic hypochromic anemias

• Low MCV, Normal MCHC – can indicate there are hemoglobinopathies


N

Iron Deficiency


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Thalassemia Minor


What’s Not OK

• MCHC > 37.5 … and what can cause it

• RBC agglutination• Lipemia• Hemolysis• Low sodium• Abnormal osmolality

(often chemotherapy)


Spin A Hematocrit

• Lipemia

• Hemolysis- redraw the sample

• Agglutination

• Abnormal sodium or osmolality

• …And if you can’t spin a HCT you could centrifuge the tube


What To Do About It

• Hemolysis• If it’s the patient- that’s a problem.• Free HGB isn’t as functional as HGB in a cell• RBC and HCT are reliable indicators• The MCV will be correct• The MCH, MCHC are not critically important at this point


What To Do About It

• Lipemia• Plasma replacement • Plasma blank • Simple math ….Hmmm


Simple Math • Based on constant ratio (2.98)

Between the MCV and MCH

• Formula can be used when

MCV is in the normal range

Corrected HGB = MCV x RBC

2.98 x 10

• Also can be used for icteric and

high WBC interference

Pathology, 1991 (23)

This is important


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What To Do If The MCV Is Not Normal

• Plasma replacement

Or try

• Dilute 1:3 or 1:5


Cold Agglutinin


Heat It

• Probably best to heat just an aliquot …


Low Sodium- 132 mEq/L Why Does That Happen?


Hypo Or Hypernatremia(Low Or High Sodium For Us Non-Chemists)

• HIGH NAIN VIVO IN ISOTONIC DILUENT RESULT

H2O OUT H2O IN

• LOW NA

H2O IN H2O OUT

HIGH HCTHIGH MCVLOW MCHC

LOW HCTLOW MCVHIGH MCHC


Sodium 132 mEq/L…How Do I Fix It?


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Sodium 132 mEq/L…How Do I Fix It?

• Recalculate indices with spun HCT

• Dilute with instrument diluent and let equilibrate


Normal SodiumNo Lipemia No AgglutinationNo Hemolysis……………NOW WHAT ?


What It Might Be And What To Do

• Look at a slide• HGB SS, C, or SC disease• Let it go (unless the MCHC is > 38)


Or…Spherocytosis


Dehydration Can Cause A High MCHC

• If the patient is dehydrated so are the red cells


What’s NOT OK

• Normal or high MCV, low MCHC• High sodium• Aged sample• Very high glucose• Very high WBC


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Sodium Of 176 mEq/L


High Glucose

• VERY HIGH…… 1494 mg/dl


Dilute The Sample And Let It ‘Equilibrate’ For 5 Or 10 Minutes

Original RBC histogram


The Really Last Resort Option Severe Cold Agglutinin


After Heating, Diluting, Replacing And All Else Fails……


Results Reported

• WBC 6.4 K/mcl

• RBC Unable to report due to severe cold agglutinin

• Hemoglobin 9.2 [g/dl]

• Hematocrit 27.5 % (spun)

• MCV Unable to report due to severe cold agglutinin

• MCH Unable to report due to severe cold agglutinin

• MCHC Unable to report due to severe cold agglutinin


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Acknowledgement

• Thank you to Jeri Walters, Technical Supervisor of Esoteric Testing at ACL Laboratories in WI, for her contribution to this presentation.


Thank You!

Any Questions?


Letting Go of the Rule of 3 CAMLT 2018 HANDOUT · 2018-09-29 · Microsoft PowerPoint - Letting Go...

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