Every day several thousand Australians will have a blood test...for everything from hepatitis to anaemia, from glandular fever to cholesterol. Some people with ongoing illnesses have regular blood tests and are quite used to it. Others are apprehensive, to say the least.
Blood tests cost our community a lot of money. However,they allow earlier diagnosis and better treatment of a whole range of medical conditions. Most doctors apply a simple rule before ordering any test, whether it be an X-ray, scan or blood test. Is this test going to help me manage this patient better? If so, get the test done.
Having a blood test or venepuncture is quite simple. An elasticized tourniquet is wrapped around the upper arm to make the veins in front of the elbow stand out. The area is wiped with an alcohol swab and a single-use, sterile needle with attached syringe is inserted into one of the veins. Blood is drawn back into the syringe and the tourniquet is released. After the needle is withdrawn, bruising is prevented by applying pressure with a cottonwool swab. The blood is emptied from the syringe into one or more tubes. It is a very minor procedure and is usually done by a trained nurse at the pathology centre.
Some of the more common blood tests are...
FBE. Full blood examination The haemoglobin level is checked and the different blood cells are looked at in detail under the microscope. Various forms of anaemia are picked up as are viral infections like glandular fever. People on some medications require regular FBE's.
U and E's. Urea and electrolytes. This test is a measure of kidney function. We see an elevated serum urea with dehydration or if the kidney function is impaired. The electrolytes are the various salts in the bloodstream... things like sodium, potassium, chloride and bicarbonate. The potassium level is of particular importance in people on diuretics or fluid tablets. Frequently the level falls in these patients and oral potassium supplements are required.
LFT's. Liver function tests. The levels of several liver enzymes rise markedly when the liver is damaged by infections like hepatitis, or by toxins like alcohol and certain drugs. Likewise, in a jaundiced patient where bile secretion from the liver is blocked, an elevated bilirubin level is seen. We also measure the protein and albumin levels; with chronic illnesses the albumin tends to gradually fall to quite low levels.
Cholesterol, triglyceride and other blood lipid levels. There is now no doubt at all that a high blood cholesterol level is an important risk factor for coronary artery disease. HDL-cholesterol seems to be protective and we like to see a higher level of this lipid. LDL-cholesterol appears a major factor in the development of coronary artery disease and we like to see a low level. Various ratios of HDL, LDL and total cholesterol are also used and may be more accurate predictors of coronary artery disease. Recent research suggests that an elevated triglyceride level is also significant and has to be taken into account.
We regularly do tests for blood sugar levels when we suspect diabetes. We do coagulation tests to investigate bleeding or bruising tendencies. Cardiac enzyme levels are done in patients with suspected heart attack. We also test for the levels of various prescribed medications, like digoxin for heart patients, and the various anticonvulsants in patients with epilepsy. In fact, there is a large number of blood tests to help in the diagnosis and treatment of most conditions. Frequently blood tests come back as normal. This does not mean that the tests were of no use. By excluding certain medical conditions we can more confidently reassure our patients. Often that reassurance can be so important.