Blood Testing

Blood is integral to every major system of your body.  Because of that, much information can be learned about your general health and diet.  This is why blood testing is often performed as it can contain markers for a variety of different diseases and illnesses.  There are a variety of tests involving your blood–I have only uncovered the tip of the iceberg.  

Blood Pressure

Blood pressure is a handy test that does not involve needles.  Blood pressure is measured using a cuff over your upper arm, called a sphygmomanometer.  The measurement involves two numbers.  120/80 mm Hg (pronounced 120 over 80 millimeters of mercury but usually people just say 120 over 80) is considered normal.  The first number, called the systolic pressure, is the measure of the pressure of your blood against the walls of your arteries when your heart is pumping.  The second number, diastolic pressure, is the pressure when your heart is not pumping.  

A sphygmomanometer / Photo available via CC0

Blood pressure fluctuates in response to many factors–emotional state, level of activity, current situation, and relative health.  Blood pressure varies minute to minute but is higher in the early morning and evenings and lower during the night.  Blood pressure drops after eating a meal.  The elderly population tends to have a higher systolic pressure which is due to increased stiffness of the arterial walls.  Children typically have a lower blood pressure than adults.  Normal readings for children are dependent on their height.  

If your blood pressure is too low, called hypotension, you may experience symptoms that include dizziness, fainting, and shock.  This is caused by a lack of blood flow to the brain.  Orthostatic hypotension, also known as postural hypotension, occurs when a person stands up from sitting.  The blood suddenly rushes down to the legs due to gravity, reducing the amount of blood the heart is pumping to the brain.  When the person is healthy, the effects (dizziness, beginning to faint) subside within a few seconds.  Pilots and acrobats may create orthostatic hypotension when doing unusual stunts which pull blood to their feet.  In any case, orthostatic hypotension can be reduced by putting the body in a horizontal position.  

Other things can have hypotension as a side effect–sepsis, hemorrhage, eating disorders, hormonal abnormalities, and toxins (including toxic doses of high blood pressure medicine).  All of these will likely require medical intervention to treat either the root cause or to manage the symptoms.  

Pilots may experience orthostatic hypertension when doing stunts that pull blood to their feet / Photo available via CC0

High blood pressure, called hypertension, is often not diagnosed as the symptoms are not obvious.  Symptoms include a morning headache, tinnitus, lightheadedness, vertigo, and altered vision.  Chronic hypertension can put you at an increased risk for kidney failure, stroke, heart attacks, heart disease, and aneurysm of the artery.  Risk factors for developing hypertension include excessive weight, excessive salt intake, chronic kidney disease, narrowing of the kidney arteries, and as a side effect of some birth control medication.  

Hypertension can be a side effect of pregnancy and some diseases.   Cushing’s disease, thyroid issues, obesity, and sleep apnea all can cause hypertension.  As can excessive consumption of alcohol, excessive consumption of licorice, and illegal drug use.

To manage hypertension, lifestyle changes are usually recommended.  Eating a healthy diet filled with fruits and vegetables helps along with reducing salt intake.  Weight loss and increased physical activity can also help to manage hypertension.    

White coat hypertension is a specific case of high blood pressure that is only present in a clinical setting.  The patient is likely agitated, stressed, and nervous about the clinical setting, causing a higher than normal blood pressure reading.  I know I have this–everything about a doctor’s office makes me nervous.  The doctor sometimes takes two or three different readings throughout the course of my visit.  The opposite of white coat hypertension is called “masked hypertension.”  Masked hypertension occurs when the reading at the doctor’s office is lower than the normal day-to-day blood pressure of the patient. 

A doctor’s white coat / Photo available via CC SA 3.0 by Samir at the English language Wikipedia

Blood Typing

Before donating or receiving blood, your blood type will need to be determined.  There are currently 33 identified blood types for humans.  The most important blood types are A, B, and O in addition to the Rhesus system, which you will usually see as Rh- and Rh+.  These designations differentiate which antigens are present on the surface of the red blood cell.  If you have type O blood, it means you have none of the antigens on the surface of your blood cell.  If you are A, you have A antigens.  If you are B, you have B antigens.  If you are AB, you have both A and B antigens.  The + and – designations are whether or not the red blood cell surface has a specific antigen from the Rhesus system, the D antigen.  If your blood is Rh-, you do not have the D antigen.  AB+ blood (pronounced “A B positive”) has all of the important antigens and is able to receive a blood transfusion from any group.  O- blood (pronounced “Oh negative”) is able to be transfused into any blood, as it has no antigens on its surface.  However, a person with O- blood is only able to receive O- blood.

ABO and Rh blood types / Photo available via CC0

In order for blood to be typed, a sample of blood is mixed separately with A blood and B blood.  If your blood clumps when mixed with A blood, you are type B.  If the blood clumps when mixed B blood, you are type A.  If the blood clumps when mixed with both, you have O.  If the blood doesn’t clump during mixing with the other blood types, it means your blood is type AB.  The Rh testing is similar.  Rh+ blood is mixed with the blood to be tested.  If it clumps, then your blood is Rh- and if it doesn’t, then the blood is Rh+.  This testing takes a few minutes to complete.  In a trauma situation when time is critical, O- blood is typically used as it won’t be rejected by the body.  This practice creates a chronic demand for O- blood donations.  

Rh testing is done similarly to ABO typing.  Rh- and Rh+ blood can create an issue between a mother and a fetus.  If the mother is Rh- and the father is Rh+, the fetus has Rh+ blood.  The mother’s body can then create an immune response attacking the Rh+ blood if the blood mixes, for example during a miscarriage or delivery.  This can then create a fetal disease called hemolytic disease of the newborn (abbreviated HDN), and the effects can range from mild to severe and can include death of the newborn.  In order to prevent this from happening, the mother is given a shot to prevent the immune response.  

Blood Tests

Blood is often drawn for analysis to help the doctor to diagnose an illness and a specific test can be performed on the blood looking for those indicators.  Other times, blood is drawn for analysis in conjunction with your yearly physical.  In this instance the doctor will often order a CBC, which is a complete blood count and maybe a BMP, a basic metabolic panel. Sometimes, fasting for 8-12 hours before the blood draw is required and your doctor should notify you of the fasting requirements as needed.  The results of the blood are typically listed as within the normal range, high, or and also, positive or negative.  Positive or negative are typically when a blood test is for a specific disease, such as HIV.  In a case similar to this, a positive result means that HIV is seen in the blood.  Interestingly, the “normal” ranges are set by that specific laboratory dependent on a number of recent blood tests performed at that lab.  This means that you could be marked as high or low if your blood is tested at one lab, but if that same blood was tested at another lab, your result could be normal.

Vials for blood draws / Photo available in the public domain

The CBC test will tell you how many red blood cells, white blood cells, and platelets that you have (more about blood and blood cells here).  A hematocrit will be also be analyzed, which is the measure of the percentage of the red blood cells versus total blood volume.  The CBC will also measure the amount of hemoglobin.  Another number on this test that you may see is the MCV, which stands for mean corpuscular volume.  This measures the size of your red blood cells.  A CBC can help detect disorders such as anemia, infections, immune system disorders, and clotting disorders.  

This diagram shows a hematocrit of 45 (red blood cells are also known as erythrocytes). / Diagram available via CC 3.0 Unported and is by KnuteKnudsen at English Wikipedia

For a BMP, the doctor will sometimes require fasting.  After the blood is drawn, the plasma is analyzed for amounts of blood glucose, calcium, and electrolytes.  The blood can be analyzed for urea nitrogen and creatinine content which is indicative of kidney function.  A BMP can detect disorders like kidney disease, diabetes, bone disease, cancer, thyroid disease, dehydration, and heart failure.  

Some more specific tests only look for one marker in the blood.  This marker could be a protein, an enzyme, an electrolyte, an antibody, or a memory cell.  Elevated levels of specific proteins in the blood are indicative of a recent heart attack.  Blood tests for a specific disease look for that specific antibody or the cell with the memory of that antibody.  When the body is fighting a disease, the body creates antibodies to fight it off.  Antibodies disappear after the threat has passed, but memories of the antibodies remain in the blood for the remainder of your life and the memory cells can manufacture the antibodies quickly if the threat comes up again.  This is also an overview of how vaccines work without you actually contracting the disease. Vaccines promote the formation of the antibodies and memories of the antibodies enabling you to fight the disease threat quickly and efficiently.  Disease specific blood tests include, but are definitely not limited to (there are many many many blood tests which can look at a specific disease), mononucleosis, celiac disease, sexually transmitted infections, and chickenpox.  

Another specific test that may be ordered is a ferritin test if you have symptoms of high or low iron.  Ferritin is different than circulating iron, as it stores the iron for your body and releases the iron when needed to make more red blood cells.  A large percentage of ferritin is stored in the liver, and when needed it bonds to transferrin.  The transferrin then transports the ferritin to the red blood cells which are being made.  Ferritin tests can be ordered if you have symptoms of low or high ferritin.  Low ferritin symptoms share many symptoms with chronic fatigue–fatigue, weakness, headaches, shortness of breath, leg pain, tinnitus, and irritability.  High ferritin symptoms include stomach pain, heart palpitations, chest pain, joint pain, weakness, and fatigue.  

Blood is often drawn for laboratory analysis during yearly physicals and to check for specific markers. / Photo available via CC0

My Conclusions

Blood testing can be a beneficial diagnostic tool, as it is affected by many different organ systems and diseases.  It shows a current profile of your general health and can indicate potential issues in a variety of body systems.

This website and information contained herein is meant for informational purposes only. You assume full responsibility and risk for the appropriate use of this information.



  1. excellent article and annual blood work is a most important screening tool for good health

Leave a Reply

Your email address will not be published. Required fields are marked *