Reference Ranges
Blood Test Results
Reference Ranges
Many lab reports include a "reference range" of values. The reference range is usually defined as the set of values that about 95 percent of the healthy population falls within. Reference ranges may vary by age group, sex and other factors for a given population. The instruments used by a laboratory to perform the tests also account for slight variations in reference ranges among different laboratories.
An example of reference ranges for blood cell counts in healthy adults are shown in the table below.
BLOOD CELL COUNTS |
| Red blood cells (per microliter [µL] of blood) | White Blood Cells (per microliter [µL] of blood) | Platelets (per microliter [µL] of blood) | Hematocrit 1 (% of blood composed of red cells) | Hemoglobin (substance in red blood cells that carries oxygen)(grams per deciliter [g/dL]) |
| Men |
4.7- 6.1 million | 5,000 - 10,000 | 150,000 - 400,000 | 42% - 52% | 14 - 18 |
Women (who are not pregnant) 2 |
| 4.2 - 5.4 million | 4,500-11,000 | 150,000- 400,000 | 37% - 47% | 12 - 16 |
Children 3 |
| 4.0 - 5.5 million | 5,000 - 10,000 | 150,000 - 400,000 | 32% - 44% | 9.5 - 15.5 |
1 The ratio of hematocrit to hemoglobin is about 3 to 1.
2 A number of changes occur in the blood of healthy pregnant women. If you are pregnant, speak to your physician about normal blood cell counts for you.
3 These ranges are for children from infancy to adolescence; speak to your physician to find out specific values for infants and young children.
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Blood Test Results
If one or more of your blood cell counts is higher or lower than normal, your physician will try to determine the reason(s). About 5 percent of healthy people will have test results that are outside of the reference range for a given test. Also, there are a number of noncancerous conditions that may cause blood cell counts to be above or below the reference range.
Here are some examples of noncancerous conditions that might cause high or low red cell, white cell or platelet counts.
| High Counts | Low Counts |
| Red Cells | Smoking, exposure to
carbon monoxide, chronic
lung disease, kidney
disease, certain forms of
heart disease, alcoholism,
liver disease or conditions
that affect the body's fluid
level. | Anemia, due to too little
iron, folic acid or vitamin
B12; bleeding; inflammatory
bowel disease; other
diseases that might cause
malnutrition; certain
medicines. |
| White Cells | Infection, inflammation,
severe physical or
emotional stress (such
as a fever, injury, or
surgery), burns, kidney
failure, lupus, rheumatoid
arthritis, malnutrition,
thyroid problems, certain
medicines | Infection, chemotherapy
and other medicines,
malaria, alcoholism, AIDS,
lupus, enlarged spleen. |
| Platelets | Bleeding, mild to moderate
iron deficiency, problems
with bone marrow
function. | Pregnancy, idiopathic
thrombocytopenic purpura,
other autoimmune
diseases, thrombotic
thrombocytopenic
purpura, hemolytic uremic
syndrome. |
Treatment with chemotherapy and/or radiation therapy for cancer can also affect blood cell counts. These measurements usually return to normal once treatment is completed.
Please see the free LLS booklet Understanding Lab and Imaging Tests if you would like to read more about blood tests.
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