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diagnostic procedures and tests
Hematocrit |
HematocritHematocrit is a test that measures the percentage of blood that is comprised of red blood cells and evaluates dehydration, polycythemia, response to anemia treatment, effectivity of blood transfusions and anemia.
The hematocrit indicates the proportion of cells and fluids in the blood and is a part of the complete blood count test.
No special preparation is necessary for this test.Blood for hematocrit may be collected either by finger prick, or sticking a needle into a vein, called venipuncture. When performing a finger puncture, the first drop of blood should be wiped away, as it dilutes the sample with tissue fluid. A nurse collects the sample following cleaning and disinfecting the skin at the needle prick site.
Fluid volume in the blood affects hematocrit values.
Hematocrit decreases in pregnancy, due to the extra fluid. The blood sample should not be taken from an arm of a patient receiving IV fluid or during hemolysis. In addition, certain drugs such as penicillin and chloramphenicol decreases the hematocrit, while glucose levels above 400 mg/dl are known to elevate results.
Decrease in the size or quantity of red blood cells reduces the space occupied, thereby resulting in a higher hematocrit.
Blood is made up of red blood cells, white blood cells (WBCs), platelets, and plasma. A decrease in the number or size of red cells also decreases the amount of space they occupy, resulting in low hematocrit.
Dehydration concentrates the blood, which increases the hematocrit. Thalassemia minor is an exception in that it usually causes an increase in the number of red blood cells, but because they are small, it results in a decreased hematocrit.
Normal values vary with age and sex being 42—60% at birth, 42-52% in adult males, 33-40% in six to 12 months and 35-47% in adult females.
Decreased hematocrit indicates iron deficiency anemianor other deficiencies. Other conditions that can result in a low hematocrit include mineral or vitamin deficiencies, liver cirrhosis, recent bleeding, and malignancies. The most common cause of increased hematocrit is dehydration and adequate fluid intake brings back the hematocrit to normal.
However, it may reflect a condition called polycythemia vera, a person has more than the normal number of red blood cells due to bone marrow problem or as compensation for inadequate lung function. Living at high altitudes causes increased hematocrit values, the body’s response to the decreased oxygen available at these heights. Consistently high values demand the guidance of a physician.
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