Knowledge Check

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Here are data showing a time-dependent increase in the mean cell volume when blood is stored at room temperature:

Stability of MCV at ambient temperature over time in 10 random samples. Source
Note the increase in MCV of about 5 fL in 30 hours!

What is happening to the mean corpuscular hemoglobin concentration (MCHC) during this time?

a
Stays the same
b
Decreases
Correct! As water moves into the red blood cells, the Hb gets diluted, leading to decreased MCHC.
c
Increases

Summary of the effect of storage time on red cell indices:

What happens to the hemoglobin and hematocrit over time with storage?

a
Hb and Hct remain unchanged
b
Hb decreases, Hct remains unchanged
c
Hb increases, Hct remains unchanged
d
Hb remains the same, Hct decreases
e
Hb remains the same, Hct increases

In a previous slide, we considered the change in mean corpuscular hemoglobin concentration (MCHC) from a descriptive standpoint – water enters cells, dilutes Hb. Now let’s formalize the concept with an equation:

MCHC = Hb/Hct

  • Hb is unchanged
  • Hct is decreased
  • Thus, MCHC must decrease

Sort the CBC parameters (top) according to the changes occurring over time with blood storage (bottom):

MCHC
Hct
MCH
MCV
Hb
Decreased
Unchanged
Increased

Let’s switch gears and consider cold agglutinins

Below are schematics of red blood cell counting in an automated analyzer from a normal individual (left) and from a patient with cold agglutinin disease (CAD; right):

What happens to the red blood cell count in CAD?

a
Stays the same
b
Artifactually low
Right! Remember the TWO HITS: big clumps of red blood cells are not being counted at all, while doublets are counted as a single cell.
c
Artifactually high

Sort the CBC parameters (top) according to the changes that occur with cold agglutinins (bottom):

MCV
RBC count
Hb
MCHC
Hct
Decreased
Unchanged
Increased

Hopefully you recalled in the last sorting exercise that the Hct is artifactually decreased in cold agglutinin disease (CAD).

Here is a very cool figure showing red cell distribution width (RDW) in a patient with cold agglutinin disease with blood incubated at various temperatures:

Volume histogram in a patient with cold agglutinin disease measured at different temperatures. Note how the RBC clumping, manifested by a second (artefactual) peak in volume, is reduced by incubating blood at increasing temperature (which causes the IgM molecules to fall of the RBCs and the clumps to dissolve) Source.

Now let’s consider hyperglycemia and hypernatremia. Sort the CBC parameters (top) according to the changes that in these conditions (bottom):

MCH
Hb
Hct
MCV
MCHC
Decreased
Unchanged
Increased

Check out these data!

MCV increases with increased concentrations of glucose. Each of the top 3 curves is derived from a different type of automated counter (from different
manufacturers). The bottom curve is based on a spun hematocrit.

What do you predict is happening to the hematocrit in the three samples above that were run on the automated analyzers?

a
Stays the same
b
Decreases
c
Increases
Correct. Water moves into red blood cells causing them to swell and increase in volume. Hct = RBC count x MCV. The red cell count does not change, only the MCV. Thus, the Hct must increase (see next slide).

You will note that the MCV (previous slide) and Hct (this slide) do not change with the spun Hct.

Let’s look at a case:

Let’s look at a case:

Note how the red cell indices correct with normalization of the blood glucose level!

Here is another case of hyperglycemia-associated macrocytosis:

Which RBC best describes the phenotype in hyperglycemia or hypernatremia  when measured in vitro (as part of a complete blood count [CBC])?

a
A
b
B
c
C
d
D
e
E

46 year-old male presented with hyperleukocytosis and leukostasis, found to have acute lymphoblastic leukemia, treated with leukapheresis.

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