|What Is A Blood Test?
A blood test is where a sample of blood is collected to check for certain conditions and diseases. The most common blood test is a blood count to detect anemia. This test can be performed using a small amount of blood from the earlobe or finger. For most blood tests however, a larger sample must be taken by needle from a vein in the arm or hand. Your doctor may perform a blood test as part of a routine checkup, or it may be done to test for something specific.
A blood test can check:
• How organs in your body, such as the liver, kidneys, thyroid gland and heart are working.
• For the presence of sexually transmitted diseases (STDs) such as HIV/AIDS and syphilis.
• For the presence or absence of hundreds of conditions such as pregnancy, diabetes, hypoglycemia, lupus, rheumatoid arthritis, cancer, coronary heart disease, hepatitis and thyroid disorders.
• If medications you are taking are working.
• How well your blood is clotting.
• Your risk of developing heart disease.
• For genetic mutations which increase your risk of developing a disease. For example genetic screening for breast cancer.
• For a hormone imbalance which could for example be a cause of infertility, or indicate the start of menopause.
How Is A Blood Test Done?
Most blood tests do not require special preparation, although some (for example, blood glucose test) may require fasting for several hours beforehand. Your doctor will let you know if this is required. During the test a sample of blood will be removed from your body. This is usually taken from a vein in the arm with a needle. First the skin is wiped with an antiseptic and an elastic band called a tourniquet is placed around the upper arm. This forces pressure to build up in the vein so that it swells with blood. A needle is inserted into the vein and a sample is withdrawn. When the needle is taken out, a cotton swab is applied to the puncture wound for a few minutes until the blood has stopped leaking. There may be some mild bruising but it will disappear after a few days. The sample is sent to a laboratory for analysis. The results can take up to 2 weeks to come back.
Does It Hurt?
It depends on your pain threshold! The most painful bit is when the needle is first pressed through the skin into the vein. As the blood is withdrawn you may feel a bit woozy. It usually helps to avoid looking at the needle, the sight of your own blood may make you feel anxious and worsen the experience. The good news? It's over in 2 minutes!
15 Common Types Of Blood Tests
The blood consists of 2 main elements: (1) a pale yellow liquid called plasma and (2) cells that float in this liquid including red blood cells, white blood cells and platelets. Blood tests that measure the cells that float are called hematologic tests. Tests done to evaluate the plasma are called blood chemistry tests.
Related: What is blood made of?
The following are some of the most common types of blood tests:
1. Complete Blood Count (CBC)
A CBC is an extensive screening done as part of a routine checkup. It evaluates the cells in your blood for signs of ill health.
Red blood cells: These cells carry oxygen around the body. Abnormal levels could indicate anemia, bleeding, dehydration or another disease.
White blood cells: These cells form part of our immune system and help fight infections. Raised levels can indicate infection, blood cancer or an autoimmune disease. A normal value of white blood cells is 3,800 to 10,800 per microliter.
Hemoglobin: This is a protein in red blood cells that carries oxygen. Abnormal levels could indicate many blood disorders including sickle cell anemia, anemia and thalassemia. A normal value is 12 to 15.6 grams per deciliter for women and 13.8 to 17.2 grams for men.
Platelets: These are sticky fragments of blood cells that seal cuts and stop bleeding. Low levels indicate a blood clotting problem and high levels indicate too much clotting (thrombotic disorder). A normal value is 130,000 to 400,000 per microliter.
Hematocrit: This indicates the percentage of red blood cells in a sample. High levels can mean you are dehydrated and low levels indicate anemia. Abnormal levels can also be a sign of a bone marrow or blood disorder. Normal values are 35 to 36 percent in women and 41 to 50 percent in men.
2. Serologic Antibody Test
This tests the serum of the blood, that is the bit of the blood that remains behind after blood has clotted and the clot is removed. It is usually done to detect the presence of antibodies. In many states a serologic test for syphilis (STS) is required to get a marriage license. The test is positive if the person has an antibody called reagin in their blood.
3. Sedimentation Rate (ESR)
The erythrocyte sedimentation rate (ESR or sed rate) is the measurement of how fast red blood cells separate and fall to the bottom of a test tube. A fast rate (15 to 20 in one hour for women and 10 to 13 for men) is associated with a variety of conditions including cancer, inflammatory bowel disease, anemia, arthritis and polymyalgia rheumatica. The ESR is not a very specific test, even if you have a high rate, it does not necessarily mean anything is wrong with you.
4. Blood Sugar Levels
Blood glucose tests measure the amount of sugar in your blood. Abnormally high levels can indicate diabetes, and very low levels indicate hypoglycemia. As spikes in blood sugar levels can occur in healthy people (due to stress and vitamin B1 deficiency for example), this test may need to be repeated several times.
What is a normal blood sugar count?
Are there any home tests for diabetes?
Hemoglobin A1C test
5. Blood Clotting Tests
Also called coagulation tests, this test checks how well your blood clots. It is done to detect the presence of liver disorders, blood clotting problems and to monitor the progress of medications taken to lower the risk of blood clots forming (anticoagulants such as warfarin and heparin).
How blood clots
6. Heart Disease Risk Tests
A lipoprotein panel looks at your risk for heart disease. It assesses your LDL (bad) cholesterol levels and HDL (good) cholesterol levels. High levels of LDL can block arteries and lead to heart attacks and strokes. Whereas HDL helps reduce the risk of blockages. Triglycerides are another type of fat molecule found in blood serum. High levels are also associated with heart disease and atherosclerosis - although the link is less clear than it is with LDL. You will usually need to fast 9 to 12 hours before this test.
7. Heart Attack Tests
A heart attack causes certain enzymes to slowly leak into your blood stream, and emergency room doctors will take a sample of your blood to check for these enzymes. These tests are referred to as CK (creatine kinase), CKMB, Troponins and C-reactive protein test. Read more about heart attack tests.
8. Blood Enzyme Tests
Enzymes are proteins that act as catalysts for chemical reactions. When organs like the liver, pancreas or heart are damaged, some of their enzymes can leak into the blood. If these enzymes are detected in a blood test it can signal disease of one of these organs. For example, raised levels of the enzyme alkaline phosphatase can indicate disease of the liver or bile ducts.
9. Kidney Tests
Blood urea nitrogen (BUN) is a product produced when proteins are broken down in the body. Normally it is excreted by the kidneys. If levels of BUN are high in the blood it can indicate a problem with the kidneys. It may also be a sign of dehydration. Another sign of kidney problems is elevated levels of creatinine in the blood. This is a product produced by the breakdown of phosphate. High levels in the blood could indicate the kidneys are not able to function normally.
10. Bilirubin Test
Bilirubin is a yellow liquid that forms when the liver breaks down old red blood cells. If the blood contains too much bilirubin it could indicate that too many red blood cells are being broken down (hemolytic anemia). Or it may be a problem with the liver (a blockage in the bile duct for example) which interferes with the normal disposal process of bilirubin and causes it to accumulate in the blood (instead of being directed to the intestines for dumping).
11. Female Cancer Test
A blood test that checks for a tumor marker called CA 125 may be used to detect female cancers. This marker is present in about 85 percent of gynecological cancers including ovarian cancer and endometrial cancer. Although an abnormally elevated level will point to cancer, it does not prove it. Other factors can cause elevated levels such as uterine fibroids, PID and pregnancy.
Electrolytes are charged molecules in the body and include chloride, potassium and sodium. People with liver disease or those taking diuretics (water pills) can have abnormal levels of electrolytes. High levels of potassium can indicate kidney disease or an underactive adrenal gland. It the levels are very low it may be a sign of liver cirrhosis, over use of diuretics, vomiting or malnutrition. An eating disorder like bulimia can lead to an electrolyte imbalances.
13. Calcium and Phosphorus Test
Abnormal levels of these minerals can indicate a problem in the body. For example high levels of calcium could be a sign of cancer, hyperthyroidism, overactive parathyroid gland or sensitivity to vitamin D.
14. Uric Acid Test
Uric acid is the final product resulting from the breakdown of DNA and RNA. Although high levels in the blood are not dangerous, they often occur in people with high risk factors for heart disease, such as hypertension, obesity and high cholesterol levels. Additionally high levels of uric acid can lead to gout or kidney stones.
15. Thyroid Tests
If a thyroid problem is suspected, your doctor will order a blood serum test. This can test for levels of the various hormones secreted by the thyroid. Usually it is done to test levels of thyroid stimulating hormone (TSH). Low levels indicate hypothyroidism and high levels are a sign of hyperthyroidism.
How thyroid disorders are diagnosed: Thyroid tests.
Tests In Pregnancy
As part of any good prenatal care program, a pregnant woman will be offered a number of blood tests. These may be done to test for the presence of STDs and rubella (both of which could be harmful to the unborn). Some doctors also recommend an AFP test at about 16 weeks to check for signs of birth defects, and a blood glucose test at 28 weeks to check for signs of gestational diabetes in the mom.