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Physical Blood Tests: Terminology

Physical Blood Tests: Terminology
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  • 0:01 Basics of Blood Tests
  • 1:22 Physical Blood Tests
  • 5:23 Lesson Summary
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Lesson Transcript
Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

This lesson is going to cover the physical properties of blood that are tested. We will look at the normal ranges and find out what abnormal test results may indicate.

Basics of Blood Tests

It is your day to learn all about blood tests. You are given the chance to shadow a phlebotomist, or healthcare professional who draws blood. The first thing that you learn from Elizabeth when you start to shadow her is that the practice of drawing blood is called phlebotomy. She insists that you become familiar with a few basic terms before you guys really get started with your day.

A venipuncture is the surgical removal of blood from a vein. Elizabeth says there are many sites to do this from, but they usually like to start with the inside crease of the elbow. There is also another common method for drawing blood used when small amounts of blood are needed. The capillary puncture is the drawing of blood from the capillaries below the skin using a short needle. The short needle that punctures just below the skin used in a capillary puncture is a lancet.

Elizabeth begins to explain how to read blood draw orders. She takes this chance to tell you that you need to prioritize your blood draws to meet the requests of the doctors. Any order that says stat needs to be done immediately.

Now that you have some basics, Elizabeth is ready to describe the different tests that explore the physical properties of blood that she performs on a regular basis in the lab.

Physical Blood Tests

The first test that Elizabeth wants to cover is the erythrocyte sedimentation rate, commonly referred to as a sed rate and abbreviated as ESR. After putting the blood into a slender tube, the sed rate is the test for how far down the tube red blood cells settle in an hour's time. This test is used to determine whether inflammation is present in the body. The further down the tube the red blood cells settle, the more the test indicates inflammation. This test can help to diagnose conditions such as Lupus and Rheumatoid arthritis.

Elizabeth is quick to let you know that a positive diagnosis cannot be made by doing the sed rate alone. The C-reactive protein test is normally used as well to help diagnose inflammatory conditions. Elizabeth goes on to explain that the test measures the level of C-reactive protein in the blood. You admit that you are completely lost on this test. Well, C-reactive protein is a protein released by the liver. The amount tends to increase when inflammation is present in the body. So the more C-reactive protein present, the more likely it is that inflammation is also present. The test helps to diagnose the same conditions as the sed rate as well as heart disease.

You recognize the name of the next test on her list to discuss with you. You tell Elizabeth that prothrombin time, or PT for short, is the test to determine the amount of time that it takes for the plasma in the blood to clot. Elizabeth tells you that the normal range of time for blood plasma to clot is 11-13 seconds. Any time it takes longer, it could mean that the patient has problems in the clotting factors, and bleeding disorders can occur. You realize that the opposite would have to be true if blood plasma clots faster than usual. It could mean the patient has clotting disorders such as thrombosis.

The total hemoglobin test is next on the list. This is a test to determine the amount of hemoglobin in a deciliter of blood. You recall learning that hemoglobin is the protein that carries oxygen on the surface of the red blood cells. She agrees and tells you that there are quite a few normal ranges for this test based on the patient's age and sex.

Elizabeth shares her little cheat sheet that lists the ranges for hemoglobin as follows:

  • adult males - 14-17g
  • adult females - 12-16g
  • children from 1 - 6 years old - 9.5-14.5g
  • newborns up to 2 weeks - 14.5-24.5g
  • newborns 2 - 8 weeks - 12.5-20.5g
  • infants 2 - 6 months - 10.7-17.3g
  • infants 6 months -1 year old - 10-14.5g

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