What is a Hemoglobin Test?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 12 November 2019
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A hemoglobin test is a blood test which is used to determine how much hemoglobin a patient has in his or her body. This test is usually performed as part of a complete blood count, a routine screening which checks on the levels of a number of blood components. Levels of hemoglobin which differ from the norm can be indicative of a wide variety of health problems, and this test can be a very useful diagnostic tool. Additionally, people may utilize hemoglobin tests to monitor the progress of various medical conditions, such as anemia.

Hemoglobin is a protein which is found naturally in the blood. It performs a number of functions, but one of the most important is the transport of oxygen throughout the body. In adults, the hemoglobin level ranges between 12 and 18 grams per decaliter, with levels being lower in pregnant women. Children tend to have between 11 and 16 grams per decaliter. It is possible for a hemoglobin test to reveal numbers which may be higher or lower than the norm.


Low levels on a hemoglobin test can indicate the presence of problems like anemia and malnutrition, while high levels are associated with things such as dehydration and heart disease. It is also possible to perform tests on the hemoglobin itself to learn more about the condition of the patient. A glycated hemoglobin or A1c test, for example, checks for the amount of glucose in the blood, an indicator of poorly managed diabetes or of increased risk of developing diabetes.

To perform a hemoglobin test, a blood sample is drawn from a patient and put through a centrifuge to separate the primary components of the blood so that they can be analyzed the tested. Multiple vials of blood may be taken if several tests have been ordered, so that only one needle-stick is needed to gather all of the samples. Once the blood has been analyzed, a printed report is prepared for a physician so that he or she can utilize the information to evaluate a patient's condition and develop a treatment plan.

A number of things can alter hemoglobin levels. The levels tend to change throughout the day, for example, which is an important consideration if someone has an unusually low or high number, but feels otherwise healthy. By interviewing the patient before ordering the test, a doctor can get an idea of the patient's general condition, and use this information to evaluate the results of a hemoglobin test.


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Post 2

It's the other way round. Hematocrit is three times the Hemoglobin. So 12*3= 36

Post 1

My recent Blood Test showed my RBC's at 3.98 Hemoglobin at 12 and my Hematocrit at 33. I am confused because I thought that the Hemoglobin was 3 times the Hematocrit. I have vonWillebrand type 1, a prosthetic mitral valve and an aortic coarctation, could this influence my results?

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