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blood smear

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BTEC National Diploma In applied Science Biomedical science techniques Blood smear Blood tests are a very useful diagnostic tool. Blood is made up of several different kinds of cells and other compounds, including various salts and certain proteins. The liquid portion of the blood is called plasma. When blood clots outside the body, the blood cells and some of the proteins become solid. The remaining liquid is called serum, which can be used in chemical tests and in tests to find out how the immune system fights diseases. Blood samples for testing can be taken either from a vein (which carries blood to the heart) or from an artery (which takes blood away from the heart). If only a few drops of blood are needed (for monitoring blood sugar in diabetes, for example) it is enough to make a small prick in the tip of the finger and then squeeze the blood out. Most blood tests are taken from a vein, commonly from those around the elbow. First a cord (tourniquet) is tied around the upper arm to make the vein prominent. It may be a bit tight, but this makes it much easier to take the test. ...read more.


repeat the process in step 2 and use a clean 1cm3 pipette add 1cm3 of the suspension from tube 1 and mix the contents of the test tube thoroughly, again label the test tube 'tube 2'. 5. repeat the process for tube 3 in a similar way 6. carefully add the drop of the suspension from the third tube onto the haemocytometer 7. then press the cover slip on the slide firmly 8. view the haemocytometer and check that the number of cells is countable 9. count the number of cells in each small square within one of the larger squares 10. count 5 large squares in total and then calculate the number of cells in the yeast suspension Results Square Number of cells 1 2,2,2,0,0,2,1,1,0,0,2,0,1,1,0,0 = 14 2 1,0,1,1,0,0,0,1,0,0,1,2,0,0,3,1 = 11 3 0,3,0,0,2,1,0,1,0,1,2,1,2,1,0,1 = 14 4 0,0,0,0,0,2,0,5,1,7,4,2,1,0,4,0 = 25 5 2,3,1,3,1,0,2,1,0,0,0,3,1,1,1,0 = 19 Calculation 1 large square = 16 small squares 5 large square = 80 small squares Total 80 volume of liquid in 1 small square = 0.05 x0.05 x 0.1mm� = 0.00025 mm� volume in 1mm� = 1.0395 = 4158 0.00025 = 1.0395 x 10� = 4150000 cells mm� 0.00025 The haematocrit test A haematocrit test measures the total volume that red blood cells take up in the blood. ...read more.


In any screening programme, there is an irreducible minimum of false positive results (wrongly reported as having the condition) and false negative results (wrongly reported as not having the condition). There are many types of cancer. To be able to screen for a particular type of cancer we must have a test that can find that particular cancer early. This is why we can't screen for all types of cancer. We do not yet have reliable tests for most of them. Once a test is found, researchers have to make sure that * The test does not say you have cancer if you do not - give a 'false positive' result * The test does not miss too many cancers - give a 'false negative' result * The test is easy to do and not unpleasant or dangerous for the people being screened * The screening test is 'cost effective' A 'false positive' result is when the screening test says you may have cancer, but in fact you don't. This causes a lot of anxiety. It also means that people have to have unnecessary tests to try to find the cancer, when they actually don't have cancer. 'False negative' results are also important because you may be reassured that you don't have cancer, when in fact you do. ...read more.

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