CE:
Phlebotomy (May 1997)
We are receiving an increased
number of under filled EDTA tubes, which causes continuing hematology problems
in the lab. Quality of results begins
with sample collection. The small purple- topped tubes hold 2 ml. blood. Two primary problems occur with under filled
tubes:
1.)
The EDTA anticoagulant used is a liquid,
which will dilute the results of the CBC.
2.) Discrepancies in PCV results
between the hematocrit centrifuge, and the Advia 120 and the Coulter T660 instruments will
occur. The excess EDTA causes the RBCs
to shrink, and they become crenated or have folded membranes. Therefore the spun PCV is falsely lowered, while the diluent in the Advia and
Coulter instruments causes the RBCs to swell to the correct size, giving a more accurate result.
The recommendation is to fill the EDTA tubes at least
halfway with blood, or use micro-collection tubes available in clin path.
CE Hematology (October 1997)
Definition of Indices: The MCV
index, MCHC index, and RDW index make up the indices of a CBC.
MCV: Mean cell (or corpuscular) volume, measured in cubic
micrometers. This is a directly measured
parameter on the Advia 120 and T660 Instruments. It is manually calculated by dividing the
packed cell volume by the red cell count and multiplying by 10. High MCV will occur in reticulocytosis,
congenital macrocytosis of poodles, FeLV infected cats, and erroneously with
agglutination. Low MCV will occur in
iron deficiency, portosystemic venous shunts, and the
MCHC: Mean cell
hemoglobin concentration, measured in grams per deciliter. This is calculated by dividing the total
hemoglobin by the hematocrit. Also calculated automatically by the Advia 120. Low MCHC will occur in reticulocytosis (immature
hemoglobin), and iron deficiency. High
MCHC is almost always a result of in vivo and in vitro hemolysis, or laboratory
error (a true increase in MCHC does not normally occur).
RDW: Red cell
distribution width, which is determined by the Advia 120 instrument. It is the coefficient of variation of the red
cell volume distribution. It is an index
of the degree of anisocytosis or variation in size of erythrocytes. Anemias with significant microcytosis or
macrocytosis will have increased RDW.
Reticulocytosis results in increased RDW.
Reference:
Hematology by the Advia 120: (February
2000)
The hemoglobin result is read photometrically. This result, and the
corresponding MCHC can be skewed because of lipemia in the blood. Therefore, in lipemic and hemolyzed
specimens, the more accurate Calculated Hemoglobin and CHCM are reported. The Advia 120 determines the density and size
of the red cells. These parameters are
not affected by lipemia. The CHCM is
derived from the Calculated Hemoglobin.
These parameters are reported in the “Tech comment” field.
CE Hematology: (December 2001)
We have noticed unusual changes of
RBC parameters in some of our “send-in” EDTA specimens for hematology in cats
and dogs. A small study revealed that if the EDTA tubes stay at room
temperature for 48 hours, an artificially induced macrocytosis might
occur. This was demonstrated on two
hematology analyzers, the Advia 120 and the Coulter Counter S+lV (no longer in use). You may get false macrocytosis in normal cats
and dogs, and possibly get false normocytosis in cats and dogs with
microcytosis. Since macrocytosis will
increase the PCV, manually obtained PCVs will also be falsely elevated.
.
Refractometers (use and care): (June
2002) These
should be checked daily with distilled or deionized water for a reading of
1.000. Tap water is not
appropriate. Calibrate if the reading
differs from 1.000 by more than ˝ of a division.