Tuesday, 9 October 2007

Blood tests

I went for some blood tests yesterday and out of curiosity fed ‘blood tests’ into Google. One of the sites it came up with was called labtestsonline.org.uk. Fascinating, I thought, what do you do? Upon investigation it offers “education and information on blood and urine tests to help patients better understand their health care.” Shame, I had lovely visions of sending blood and urine over the phone lines...
After visiting Wikipedia and others I can summarise what Blood tests are about. They are laboratory tests done on blood to gain an appreciation of disease states and the functioning of various organs. Blood flows through the body and acts as a medium for providing oxygen and drawing waste products back to the excretory systems. As a consequence the state of the bloodstream affects, or is affected by, many medical conditions. For this reason blood tests are one of the most commonly performed medical tests.
Blood is obtained from one of the patient’s veins by venipuncture or fingerprick, except for tests such as Arterial blood gas which require arterial blood. Blood tests are a relatively non-invasive way to obtain cells and to extract extracellular fluid (plasma), from the body to check on its health. Although the term blood test is used, most routine tests (except for most haematology) are done on plasma or serum. (Only 40% of the blood’s volume is made up of blood cells – red, white and platelets – the majority is plasma which is water with proteins and chemicals such as hormones, glucose and salt.
A basic metabolic panel (BMP), also known as a Chem-7, is a set of seven blood chemical tests designed to measure sodium, potassium, chloride, bicarbonate, blood urea nitrogen, magnesium, creatinine, and glucose. Calcium is often also routinely measured though it is not strictly speaking in a Chem-7. Most people will have heard of all the above except creatinine which is a breakdown product from creatinine phosphate in muscle and is usually produced at a fairly constant rate. It is mainly filtered by the kidney and if the filtering of the kidney is deficient blood levels rise.
Although various healthcare professionals can take extract the blood the specialist in the field is the phlebotomist and our GP’s practice has one who visits on a regular basis. If venipuncture is done properly there should be no lasting impression though it is sensible not to lift anything heavy with that arm for an hour or so. Done badly it can leave you with a sore and bruised arm for days. Fortunately our phlebotomist is not only a very pleasant soul but good at her job. The only time I have been bruised was when a Sister at Walton hospital took the sample and took her revenge on me for being kept back late to take the sample to the lab.
For more information (though you've probably already had too much) - see

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