9.3 Parameter Limitations (continued)
As HCT is the product of MCV x RBC, any erroneous result in MCV and/or RBC will produce an equal error in
the HCT parameter.
Red Blood Cell
Agglutination
Agglutination of RBC may produce an erroneous MCV value and therefore a false HCT.
An excessive number of WBCs might cause interference within the RBC population and
therefore a false MCV value.
Thrombocytosis
(elevated PLT)
Excessive numbers of PLT, in most cases, do not interfere with the MCV parameter due
to the use of the floating discriminator technology in the instrument.
Measurement of low PLT levels may be influenced by circulating RBCs, which may cause falsely high results.
Measurement of high PLT levels is influenced by coincidence factors (e.g. counting of two cells as one) which
may produce falsely low results. The instrument is compensated for these effects by separate algorithms to
produce linearity ranges according to the specifications
Microcytosis (small
RBC, low MCV)
Very small RBCs might falsely elevate a PLT count and affect the MPV. This effect is
minimized in the instrument due to the use of a floating threshold (discriminator). By
observing the PLT and RBC histograms, this effect is seen as an overlapping PLT/RBC
area.
Agglutinated RBCs might trap platelets and may give an erroneous low PLT count and
affect the MPV. The presence of agglutinated RBCs is detected by monitoring the
MCHC parameter and by careful examination of the stained blood film.
Giant platelets in
excessive numbers
This may cause a low PLT count since they might fall within the RBC threshold range.
Cytotoxic and immunosuppressive drugs may increase the fragility of these cells, which
may cause low PLT counts. Reference (manual) methods may be necessary to obtain an
accurate platelet count.
Hemolyzed specimens contain red cell stroma, which may elevate platelet counts.
Blood anti coagulated with Acid Citrate Dextrose may contain platelet aggregates,
which could depress the platelet count.
Erythrocyte inclusions may also produce a spuriously increased platelet count. (e.g.
Howell-Jolly bodies, siderotic and basophilic granules)
Clumped platelets due to poor collection techniques or platelet satellitosis caused by
EDTA activation of immunoglobulins may cause a decreased platelet count and/or an
elevated WBC count. The specimen should be recollected in sodium citrate
anticoagulant and re analyzed for only the platelet count. The final PLT result must be
corrected for the sodium citrate dilution effect.
Large platelets counted as RBCs will fall outside the PLT range and therefore lower the
MPV.
Very small RBCs might fall into the PLT region and might be counted as PLTs and
therefore influence the MPV parameter.
Agglutinated
erythrocytes
This may trap platelets and therefore affect the MPV parameter. Note that agglutinated
erythrocytes may be detected by carefully examine the MCHC parameter and/or the
stained blood film.
May also effect the size of the PLTs.
Note that all samples collected in EDTA will not maintain a stable MPV. The PLTs will
swell as a function of time and temperature.
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