Reasons you may not be able to
have the test or why the results may not be helpful include:
If the elastic band was on your arm a long time
while the blood sample was taken.
Taking medicines that can cause low platelet levels. Some
examples of the many medicines that cause low platelet levels include steroids, some
antibiotics, thiazide diuretics, chemotherapy
medicines, quinidine, and meprobamate (Equanil, Miltown,
A very high white blood cell count or high levels of a
type of fat (triglycerides). These can cause falsely high
Pregnancy, which normally causes a low RBC value and less
often a high WBC value.
Clumping of platelets in the test tube.
This can cause a falsely low platelet count and occurs because of the substance
used in the test tube.
What To Think About
The white blood count can change by as much as
2,000 WBCs per microliter (mcL) from exercise, stress, or
Children normally have higher WBC (leukocyte) counts than
Other red blood cell tests that may be done include:
Erythrocyte sedimentation rate (ESR). An
ESR test measures how quickly red blood cells (erythrocytes)
settle in a test tube. When
inflammation in the body is present (such as from an
infection or cancer), red blood cells may settle more slowly than normal. An
ESR may help find certain inflammatory diseases when CBC results are normal.
For more information, see the topic
This test counts the number of immature red blood cells (reticulocytes) in a
blood sample. Generally, only a few reticulocytes are present in the blood in
relation to mature red blood cells. But recent bleeding or mature red blood
cells being destroyed can cause a lot of new reticulocytes made. This test can
help find some types of anemia and check how well treatment is working. For
more information, see the topic
Hematocrit measurements can be very different
depending on the method and type of machine used to do the test.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.