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Medical Author:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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In most labs, the hematocrit is measured by a machine that automatically determines a variety of blood tests referred to as the complete blood count (CBC). The complete blood count is a numerical listing of the hematocrit as well as the hemoglobin concentration, and the three blood cell lines produced by the bone marrow (the red blood cells, the white blood cells, and the platelets).

Another simple method used in Emergency Departments is termed the spun hematocrit or "spun crit." A small amount of blood (about 0.05 to 0.1ml) is placed in a thin capillary tube, the tube sealed with wax or clay and placed in a centrifuge. The red cells collect at the bottom and form a red column and are separated from the straw-colored serum column by a small area composed of white blood cells; the height of the total capillary blood column (red cells, white cells and serum equals 100%). The height of the red cell column divided by the total capillary column height equals the hematocrit (percentage of RBC's in the total blood volume). This test can be performed in a few minutes.

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