It is possible to count reticulocytes by precipitating
the residual RNA using new methylene blue to form a
reticular network in the cell. There are numerous
reticulocytes in this field. A normal reticulocyte count is
often expressed as a percent of total RBCs (normal 0.5-1.5
%), but may be expressed as an absolute number (normal
Every 24 hrs approximately 2 x10 RBCs are generated,
replacing over 1% of the red cell mass. Over 95% of RBCs are
found in the peripheral blood where the erythrocyte
functions during its life span of 120 days.
How might you use the reticulocyte count (decreased,
normal or increased) in evaluating a patient with too few
RBCs? Then try the case below.
You are the Doctor:
Your patient is a 44 year -old woman complaining
of "exhaustion". Her hematocrit is 0.15, her RBC
count 1.0 million and her reticulocyte count 2%.
You decide that her reticulocyte count is increased
and determine that there is no evidence of
bleeding. The increased reticulocyte count would
indicate that her marrow is responding with
acclerated erythropoiesis. Thus you decide to watch
and wait. But that night you realize your mistake
in regard to the reticulocytes! What was wrong?
You decided that the 44 year -old woman with a hematocrit
of 0.15 and a reticulocyte count of 2% had an increased
reticulocyte count indicating that her marrow is responding
with increased RBC production thus you decide to watch and
wait. What was wrong in regard to the reticulocytes?
AHHH HA! When expressed as a % of total RBCs the
reticulocyte count may overstate the actual number of
In this case:
Thus the retic count is not increased (normal being
0.5-1.5%), but is in fact relatively low in an anemic
patient indicating no marrow response and suggesting marrow
The use of the absolute rectic count avoids this problem.
In this case:
(0.02 x 1,100,000) = 22,000 retics, which is abnormally
low for someone with such a low Hct.
If RBCs are destroyed as in a hemolytic anemia, or lost
as in a GI bleed
the rate of erythropoiesis may increase as much as 8
fold. This is known as accelerated erythropoiesis and is
secondary to the increased input of stem cells and a
shortened precursor generation time. After a brief lag
period increased RBC precursors appear in the bone marrow
(lower left). Compare the erythroid hyperplasia with a
normal marrow on the right.
Normally, there are three myeloid precursors for each
erythroid precursor resulting in a 3:1 ratio, known as the
M:E (myeloid to erythroid) ratio.
Accelerated red cell production would be expected to:
The major regulator of erythrocyte production is
erythropoietin. Erythropoietin stimulates the
differentiation of committed erythroid stem cells (CFU-E)
into red cell precursors. The production of erythropoietin
is mediated by tissue oxygen levels such that RBC production
exactly balances RBC loss, maintaining sufficient oxygen
delivery to body tissues.
When blood is destroyed or lost:
1. the O2 receptor detects insufficient tissue
2. erythropoietin production increases;
3. which increases committed erythroid stem cell
4. restoring red blood cell mass to normal.
While working for NASA you take part in a short-term
high altitude simulation study. Check your Hct, at right. Is
It's a busy August night in the ER; you're juggling 3
Patient 1: A 22 yr old man is bleeding profusely from a
Patient 2: A 24 yr old pregnant woman in her 8th month is
hypertensive and is retaining fluid.
Patient 3: A 26 yr old cyclist collapsed after a
gruelling race. The cyclist dies.
You spin the Hcts, but do not believe the results. Did
you mix them up?
A. Pt samples 1 and 2 reversed.
B. Pt samples 2 and 3 reversed.
C. Pt samples 1 and 3 reversed.
D. Pt sample1 belongs to 2; 2 to 3, and 3 to 1.
E. Correct as is.
The Hematology Laboratory confirmed your spun
hematocrits, but you noticed that the values from the
laboratory were 1-2 % lower than the spun Hcts. Do you
The function of the erythrocyte is to produce, package,
protect, and transport hemoglobin between the various body
The normal mature erythrocyte is a biconcave disc
approximatly 8 um in diameter; 2.5 um thick at the periphery
and 1.0 um thick at the center. Each contains 27-34 pg
(10-12 g) of hemoglobin representing about 95% of
the dry weight of a RBC.
For information regarding erythrocyte metabolism and
hemoglobin click the Erythrocyte button.
Sophisticated automated partical counters determine
directly the number of RBCs; RBC size or Mean Corpuscular
Volume (MCV) and hemoglobin (Hgb) content.
Other RBC parameters are calculated,ie. Mean Corpuscular
Hemoglobin (MCH) and Mean Corpuscular Hemoglobin
Concentration (MCHC). In automated instruments the Hct is
MCV gives you the average volume of erythrocytes.
MCH gives you the average weight of Hgb per eyrthrocyte.
MCHC gives you the average Hgb concentration per
Automated instruments measure cells using either
electrical impedance or LASER techology.
This is a typical automated instrument report screen.
Looking only at the RBC parameters, we see a % RDW which
is the coefficient of variation (CV) about the MCV. Thus the
RDW is a quantitative measure of RBC size variation
(anisocytosis). The RBCc, MCV, MCH and RDW are numerical
correlates of RBC variations of #, size, Hgb conc. and
shape, as seen on Wright's stained peripheral blood (PB)
Notice the normal, minor variations in RBC size
(anisocytosis) and shape (poikilocytosis). The area of
central pallor is usually 1/3 the RBC diameter, reflecting
normal Hgb content.