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Causes of Low Hematocrit Blood Test Results

Author:   Peter Sedesse MD

Normal Hematocrit Blood Test Levels

A hematocrit test measures the percentage of your blood that is composed of red blood cells.  In healthy men, this value will be between 38.8 and 50%, and in women between 34.9 and 44.5%.  The hematocrit test is sometimes called a PCV or Packed Cell Volume because the test is performed by spinning the blood in a centrifuge and then measuring the red blood cells which are packed at the bottom of the test tube.  There are a few normal occurrences which can alter the hematocrit test result.  People living in higher elevations will have a higher hematocrit level because the body will manufacture more RBCs to account for the lower oxygen levels in the air.  Pregnancy can also alter hematocrit levels and likewise, hydration levels will effect the hematocrit test results.  Patients who are extremely dehydrated will have an elevated result.

Decreased Red Blood Cells as a Cause of Low Hematocrit Test Results

The most obvious cause for a low hematocrit test result is an anemia, a disease or condition that reduces the number of red blood cells in the body
.  There are many different types of anemia caused by different things.  Sickle cell anemia is caused by a genetic defect.  There are also other anemias caused by deficiencies of Vitamin B12, B9 and Iron.  Finally, anemia can be caused by issues with the bone marrow, including disease or radiation treatments or exposure

Infections and Hematocrit Test

Since the Hematocrit test measures the percentage of the blood that is composed of red blood cells, anything that elevates the other parts of the blood, will obviously reduce the percent of RBCs present.  Normally white blood cells are a very small percentage of blood, but some chronic or severe infections can cause the number of white blood cells to increase so drastically as to push the percentage of RBCs below normal limits 

Obviously in the case of an infection that severe, the low hematocrit level would not be revealing or surprising.  Lymphoma and Leukemia are other conditions which can greatly increase the white blood cell percentage of the blood and cause a low hematocrit test result.

Blood Loss as a Cause for a Low Hematocrit Blood Test Result

The final reason for a low hematocrit test result would be because of blood loss.  When blood is lost in the cardiovascular system, the first and most important response of the body is to retain blood volume and pressure.  It does this primarily by pumping water into the veins and arteries, and then gradually over time, the bone marrow replaces red blood cells to normal levels.  During the time immediately after bleeding, the water portion of blood will be increased and RBCs will be decreased.  This will happen following traumatic blood loss like an accident, and also from blood loss following surgery.  A low hematocrit test result will also be seen in a patient who is bleeding internally or through ulcers in the digestive tract, as seen in colon cancer.  In those cases, the body is constantly needing to add water to the blood to maintain blood volume and pressure, but cannot manufacture red blood cells fast enough to keep hematocrit percentages at normal levels.

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