A hemoglobin test is the assessment of the rbc percentage in total blood volume.
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The HCT is a measurement of the volume of red blood cells as a percentage of whole blood. For automated procedures, the haematocrit is the product of the RBC and the mean cell volume (see below). For manual determinations, the haematocrit is measured after centrifugation of a microcapillary tube filled with whole blood. The percentage of blood composed of red blood cells is the haematocrit (sometimes called packed cell volume). Manual or ‘spun’ haematocrits tend to be a few percentage points higher than calculated haematocrits, because trapped plasma is included in the apparent red blood cell volume. Haematocrit is expressed as a number without units between 0.00 and 1.00. Haematocrit values for mice are generally between 0.40 and 0.50, but may range up to 0.60 depending on sampling site and fasting status. Show
View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780123820082000143 Diagnostic radioisotopes in haematologyInderjeet Dokal, S. Mitchell Lewis, in Dacie and Lewis Practical Haematology (Tenth Edition), 2006 Whole-Body and Venous Packed Cell Volume RatioPCV measured on venous blood is not identical with the average PCV of all the blood in the body. This is mainly because the red cell:plasma ratio is less in small blood vessels (capillaries, arterioles, and venules) than in large vessels. The ratio between the whole body PCV and venous blood PCV is normally about 0.9,9 and it is thus necessary in the calculation of TBV from measurements of RCV to multiply the observed PCV by 0.9. Thus, TBV is given by the following: Red cell volume ×1PCV×0.9 However, the ratio varies in individuals, especially in splenomegaly, and it is better to estimate RCV and plasma volume by separate measurements rather than to attempt to calculate one of these from an estimate of the other. View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B0443066604500192 The complete blood count and white blood cell differentialAlisha D. Ware, in Contemporary Practice in Clinical Chemistry (Fourth Edition), 2020 HematocritThe hematocrit is the percentage of packed RBCs in the whole blood [17]. The hematocrit has the implied units of L/L, although it is usually reported as a percent. Prior to the use of modern analyzers, the hematocrit was measured by centrifuging a tube of blood, and measuring the proportion of RBCs, which would settle to the bottom of the tube, to the total volume of blood. On modern hematology analyzers, the hematocrit is a calculated value [5,18,19]. A simple equation to calculate the hematocrit percent is to multiply the RBC count (in cells/L) by the MCV (in fL). Hematocrit=RBCCount(inRBCs/L)×MCV(infL) Sample calculation for an RBC count of 4.68 × 1012/L and an MCV of 84.8 fL: Hematocrit=4.68×1012/L×84.8×10–15L=0.397L/L(or39.7%). View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780128154991000259 PRINCIPLES IN ASSESSING MUSCULOSKELETAL DISORDERSRONALD C. EVANS D.C., F.A.C.O., F.I.C.C., in Illustrated Orthopedic Physical Assessment (Third Edition), 2009 HematocritDecreased hematocrit indicates anemia, such as that caused by iron deficiency or other deficiencies. Further testing may be necessary to determine the exact cause of the anemia. Other conditions that can result in a low hematocrit include vitamin or mineral deficiencies, recent bleeding, cirrhosis of the liver, and malignancies. The most common cause of increased hematocrit is dehydration, and with adequate fluid intake, the hematocrit returns to normal. However, increased levels may reflect a condition called polycythemia vera—that is, when a person has more than the normal number of RBCs. Increased hematocrit can be caused by a problem with the bone marrow or, more commonly, as compensation for inadequate lung function (the bone marrow manufactures more RBCs to carry enough oxygen throughout the body). A hemoglobin test measures the levels of hemoglobin in your blood. Hemoglobin is a protein in your red blood cells that carries oxygen from your lungs to the rest of your body. If your hemoglobin levels are abnormal, it may be a sign that you have a blood disorder. Other names: Hb, Hgb What is it used for?A hemoglobin test is often used to check for anemia, a condition in which your body has fewer red blood cells than normal. If you have anemia, the cells in your body don't get all the oxygen they need. Hemoglobin tests are measured as part of a complete blood count (CBC). Why do I need a hemoglobin test?Your health care provider may order the test as part of a routine exam, or if you have:
What happens during a hemoglobin test?A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes. Will I need to do anything to prepare for the test?You don't need any special preparation for a hemoglobin test. If your health care provider has ordered other tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your health care provider will let you know if there are any special instructions to follow. Are there any risks to the test?There is very little risk to having a blood test. After the test, some people experience mild pain, dizziness, or bruising. These symptoms usually go away quickly. What do the results mean?There are many reasons your hemoglobin levels may not be in the normal range. Low hemoglobin levels may be a sign of:
High hemoglobin levels may be a sign of:
If any of your levels are abnormal, it doesn't always mean you have a medical condition that needs treatment. Diet, activity level, medicines, a menstrual period, and other factors can affect the results. You may also have higher than normal hemoglobin levels if you live in a high altitude area. Talk with your provider to learn what your results mean. Learn more about laboratory tests, reference ranges, and understanding results. Is there anything else I need to know about a hemoglobin test?Some forms of anemia are mild, while other types of anemia can be serious and even life threatening if not treated. If you are diagnosed with anemia, be sure to talk to your health care provider to find out the best treatment plan for you. References
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