What Can a Blood Test Tell You?
What Blood Tests Show
Blood tests can show a lot of information about what’s going on in your body, including general health facts and clues about possible issues.
Blood tests help your doctor know the following:
How well organs are functioning
The presence of certain diseases or conditions, such as cancer, diabetes, or anemia
The risk of heart disease
Whether certain medications are working
How well your blood is clotting
Most Common Blood Tests
When you go for a yearly physical checkup, your doctor will likely order a set of routine blood tests. According to the Cleveland Clinic Martin Health Organization, the most common blood tests are the following: 3
Complete Blood Count (CBC)
This blood test is probably the most common one. It counts the number of cells in the blood and their type, including red and white blood cells plus platelets. This test will usually include the RDW blood test and the MCV blood test. The CBC will also test your MCH levels.
Prothrombin Time (PT)
Measures the time it takes for your blood to clot. It looks for the activity of five different items in the blood that affect clotting.
Basic Metabolic Panel
Looks at your body’s amounts of glucose, sodium, potassium, and other materials that keep you healthy.
Comprehensive Metabolic Panel
Adds six more tests to the basic panel to look more closely at how your organs are working.
Helps assess your risk for cardiac diseases.
Thyroid Stimulating Hormone (TSH)
Measures how your thyroid is functioning.
Can be used to detect and keep track of diabetes issues.
Things To Know About a Complete Blood Count
A CBC helps doctors know more about your general state of health. It also can assist in detecting any possible disorders and outline current nutritional status.
When symptoms such as tiredness, weakness, and bruising exist, a CBC can help in diagnosing conditions such as anemia, leukemia, malaria, or infection.
Here are the specific things measured in a CBC lab test. 4
Red Blood Cells
These cells carry oxygen from the lungs and into the rest of the body. If your CBC shows that the red blood count is lower than normal, this could be a sign of anemia, dehydration, blood loss, or some other disorder.
Normal Ranges for Red Blood Cell Count
The normal ranges for red cells are different for males and females. For males, 4.7-6.1 million cells per microliter count is normal, while for females, 4.2-5.4 million is normal. A low red blood cell count can indicate anemia, a condition that causes fatigue, dizziness, heart palpitations and feelings of weakness. Abnormally high red blood cells counts can be due to a heart condition, bone marrow disease, cigarette smoking, kidney issues, or dehydration. 5
White Blood Cells
As part the body’s immune system, white blood cells work to fight off infection and disease. If this blood count is too low, it may mean there is an infection in the body, cancer of the blood, or an immune system disorder. If your doctor orders a CBC with differential lab test, the amounts of different kinds of white blood cells are then examined.
Normal Ranges for White Blood Cell Counts
White blood cells are called leukocytes. There are five main types of these infection-fighting cells in the blood:
The normal levels of white blood cells range from 4,500 to 11,000 per microliter (e.g. 4.5 to 11.0 x 109/L). If your numbers are between 4.5 and 11, this is considered normal. When there is a low WBC count below 4.5, this can be caused by several things, including:
When the WBC is too high (above 11.0), it can be due to smoking cigarettes, a bacterial infection, an inflammatory disease, certain cancers, or drugs being taken that can increase white blood cells, such as: 6
Parts of blood cells that help with blood clotting are called platelets. When a cut on the skin occurs, platelets eventually stick together to stop the bleeding if platelets levels are normal. Platelet levels that are too low can be signs of a bleeding disorder. If the levels are too high, it may mean there is too much clotting going on.
Normal Ranges for Platelet Count
A healthy platelet count ranges from 150,000 to 450,000 per microliter of blood. If your count is too high, it may mean you have thrombocytosis, a condition possibly caused by anemia, cancer or infection.7 If the count is too low, it’s called thrombocytopenia. This may be due to medications you’re taking, a genetic condition, certain cancers, chemotherapy treatments, kidney infection, or drinking too much alcohol.
The hemoglobin in blood is a protein that is full of iron. It helps the cells transport oxygen. If hemoglobin levels are too low, it may be a sign of anemia, sickle cell anemia, or another blood disorder.
Normal Ranges for Hemoglobin Count
Normal hemoglobin counts are 14-17 grams per deciliter for males and 12-15 for women. A count that’s too high may indicate conditions related to bone marrow, lung, heart, or kidney conditions. A lower than normal count can be due to anemia.
Red blood cells take up a certain amount of space within the blood. Hematocrit levels are measured to decide how much space is taken up. If hematocrit levels are too high, it is a sign of dehydration. If the levels are low, it can signify anemia. There is also a chance that abnormal hematocrit levels point to a blood or bone marrow issue.
Normal Ranges for Hematocrit Count
These results are shown as a percentage of the number of red blood cells in 100 milliliters of blood. A normal range is 45-52% for males and 37-48% for females. A low hematocrit count indicates anemia. A high count can usually be seen in people who live at high altitudes, who smoke cigarettes, with rare cases due to lung disease and bone marrow disorders.
Mean Corpuscular Volume (MCV)
The average size of red blood cells is measured with this test. If MCV levels are abnormal, it may point to anemia or a blood disorder.
Normal Ranges For MCV
This number represents the size of your red blood cells as they travel through the bloodstream. A high number means the cells are larger than average, while a low number means the opposite. A high MCV can be due to certain anemia such as a Vitamin B12 deficiency. A low MCV may mean there is an iron deficiency.
Basic and Comprehensive Metabolic Panel
You have to fast from eating and drinking for about 12 hours before your blood is drawn for this test.
The basic metabolic panel (BMP) looks at the body’s:
Glucose (sugar) levels
Your body uses glucose for energy. Electrolytes keep body fluids balanced. They also regulate heart rhythm, the ways your muscles contract, and brain functioning. Your kidneys maintain the correct balance of water, sodium, and minerals in the blood. This organ also cleans waste and unwanted substances from the blood.
Knowing that your blood sugar, electrolytes, and kidneys are working normally at the correct levels is important. If you are on any kind of medication, your doctor may order a basic metabolic panel to ensure your kidneys and electrolytes aren’t being negatively affected. This test is also commonly used to detect medical conditions.
The basic panel measures glucose and blood urea nitrogen (BUN) levels in the blood. It also checks the levels of:
A comprehensive metabolic panel (CMP) also measures levels of:
These extra tests help indicate problems with the liver or kidneys.
Other Important Blood Tests
Prothrombin Time Blood Test
This test, also known as a PT/INR blood test, measures how long it takes for the liquid part of your blood (plasma) to clot. The liver releases a protein called prothrombin, which is one of the means by which the blood clots properly.
PT stands for pro time test. If you take a blood-thinning drug, the test results will be shown as a number ratio known as the international normalized ratio (INR). Most people are recommended to take a prothrombin blood test in order to see if their blood thinners are working correctly, to diagnose liver problems, or to see if blood is clotting normally prior to surgery.
The American Heart Association advises adults over the age of 20 to have their cholesterol levels taken. 8 A lipid panel is basically a test to show how much of the different types of cholesterol you have in your blood.
A lipid panel shows the blood’s amounts of:
This information is important, as abnormal cholesterol levels can be signs of heart disease.
If your doctor orders a comprehensive metabolic panel, a liver panel test measures the same six substances in the blood. When ordered on its own, it’s called a liver panel or liver function test.
This test may be necessary if symptoms of liver disease appear, such as:
You may also need a liver panel if you’ve been exposed to hepatitis. The test also checks liver function if you are taking a medication that is known to cause liver damage.
The thyroid helps regulate the way our bodily cells change nutrients into energy. It manages our body temperature, heart rate, and brain function.
Low levels of the thyroid hormone can cause the following symptoms:
These symptoms may point to hypothyroidism. Women are more likely to have low thyroid levels in their blood than men. It’s a recommended test to have, especially if you are a woman over the age of 60 or if your LDL cholesterol levels are getting higher. 9
Hemoglobin A1c Test
Hemoglobin is a protein. It’s found in red blood cells, and it’s what gives your blood its red color when it’s exposed to oxygen. The job of hemoglobin is to carry oxygen through the body. This test measures how much of your hemoglobin is coated with sugar. It’s a necessary test for people with diabetes. It’s also a blood test used to diagnose diabetes. The results show if you’re at risk for prediabetes or type 2 diabetes.
Red blood cells live for about 12 weeks, so the Hemoglobin A1c tests shows your glucose levels for the past three months. The Center for Disease Control advises the Hemoglobin A1c test for managing diabetes and as a baseline test for someone who is over the age of 45 and has risk factors for diabetes or has had gestational diabetes. If you are prediabetic, it’s good to have this test performed every 1 or 2 years.10
How Blood Testing Works
For most common blood tests, no special preparation is needed. Some tests do require that you not eat or drink for 9-12 hours before your blood is drawn. You also may not be allowed to take certain medications prior to the blood test. Your doctor or the testing lab will inform you of any preparation that might be necessary.
Where Do They Take the Blood From?
Having a blood test done takes only a few minutes. The blood is usually taken from a vein in your arm, typically not from your dominant arm. For instance, if you are right-handed, the blood will be drawn from your left arm. With some blood tests, the fluid can be taken from the tip of a finger with a quick prick.
Before the lab worker takes your blood, he or she will tie an elastic band around the upper part of your arm and ask you to make a tight fist with that hand. This is done so your veins become more visible, making it easier to see where the needle should go in.
A small test tube is attached to a needle for collecting the blood. It’s very possible that more than one test tube will be needed to collect the amount of blood needed for all of the blood tests required. The person inserts the needle into the vein and removes the tube when enough blood has been collected. A second or third tube can quickly be replaced to draw more blood. The entire procedure takes no more than three minutes to complete.
When the needle is withdrawn, the technician will press a gauze pad on the arm site to be sure the bleeding stops. You may be asked to apply pressure there for a moment. A bandage will then be placed over the gauze, which you can leave on for a few hours if desired.
Blood Tests That Require Fasting
A number of blood tests typically require fasting for a number of hours before blood is drawn. Most allow a few sips of water, especially if you need to take a pill, though some medications should not be taken prior to blood work tests. A normal MCV is 80-96 femtoliters (cubic micrometers) per cell.
The tests that will usually require fasting are:
Blood Glucose Tests
Renal Function Panel
If you need to fast before a blood test, it’s a good idea to schedule your test early morning. That way, the fasting is mostly done overnight while you sleep. It’s important that you don’t eat breakfast or even drink coffee on the morning of the test. The caffeine in coffee can interfere with blood test results. Coffee also tends to dehydrate, making it more difficult for the lab technician to find your vein.
When being tested for liver health or to check on triglyceride levels, you may be asked not to drink any alcohol for 24 hours beforehand. You should also ask whether you can smoke cigarettes during any fasting for blood testing.
Questions To Ask About Blood Test Results
Even if you get a phone call from your doctor’s office telling you that your blood tests came back normal, you may want to ask to speak with your physician about the results. Some questions to consider are:
“Was there anything abnormal in my results?” If something is borderline or out of range at all, you should know it and ask what you can do about it.
“Do the results explain any of the symptoms I’ve been having?” If you’ve been feeling sluggish, your blood work results may show a clue as to why you’ve been experiencing fatigue.
“Should I be making any lifestyle changes based on these results?” You’ll want to know if your doctor has any suggestions on how to prevent potential disease or disorders. Perhaps you should be adding specific vitamins or exercise to your lifestyle.
“How do my results line up with my family medical history?” You’ll want to know this to find out if you’re at risk for certain diseases that run in your family.
Blood Tests Support Wellness
Blood tests are some of the many tools that doctors use to help diagnose their patients and prevent future issues that may interfere with their overall health. Although the lab results that come back to your doctor may indicate that everything is fine, it’s always a good idea to have a conversation if you are in doubt about a specific symptom or issue.
Blood tests are just one of many ways to oversee a person’s wellness. Physical exams and good communication with your health provider are also important in diagnosing physical and emotional wellbeing.