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Blood Tests: Why, When, and What to Expect

Learn all about Blood Test, What they are, When do you need, Common Blood Tests, and more.

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BodyBrainAI Team03 Mar 2023
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Overview


Blood tests are common medical procedures used to check for signs of illness, disease, infection, and other health conditions. By analyzing a sample of your blood, doctors can gain valuable insights into what's going on inside your body. Read on to learn more about why blood tests are performed, when you may need one, and what to expect during the process.

What are blood tests?


Blood tests involve taking a blood sample, usually from a vein in your arm, and sending it to a lab for analysis. The lab can measure levels of different components in your blood, such as:

  • Red blood cells, which carry oxygen

  • White blood cells, which fight infection

  • Platelets, which help blood clot

  • Plasma, the liquid portion of blood

  • Hemoglobin, which gives blood its red color

  • Electrolytes like sodium, potassium, chloride

  • Proteins like albumin and globulin

  • Hormones like insulin and cortisol

  • Vitamins and minerals like iron, folate, magnesium

  • Enzymes that indicate organ function

  • Metabolic waste products like creatinine

  • Genetic material like DNA

By looking at any abnormalities in these components, blood tests can reveal problems with circulation, immunity, metabolism, hormones, kidneys, liver and more. They are a vital diagnostic tool for doctors.

When would I need to have a blood test?


There are many reasons your doctor may order a blood test, including:

  • Part of a routine physical exam to evaluate overall health

  • Screening for diseases you may be at risk for

  • Investigating the cause of symptoms you're experiencing

  • Monitoring an existing health condition

  • Checking organ function and electrolyte levels

  • Evaluating treatment effectiveness

  • Looking for genetic mutations linked to disease

  • Required for certain jobs, insurance applications, travel visas

Blood contains a wealth of information and can point to issues before symptoms even develop. That's why regular blood screening is recommended based on your age, health status and risk factors.

What are the most common blood tests?


Some of the most common blood tests include:

  • Complete Blood Count (CBC): Measures levels of blood cells and checks for anemia, infection, blood cancers.

  • Basic Metabolic Panel (BMP): Checks electrolyte and fluid balance, kidney function, blood sugar

  • Comprehensive Metabolic Panel (CMP): Measures kidney and liver function, electrolyte levels, blood proteins.

  • Lipid Panel: Measures cholesterol levels and heart disease risk.

  • Thyroid Panel: Evaluates thyroid gland function and hormone levels.

  • Liver Function Tests: Assess liver enzymes to check for liver injury or disease.

  • Blood cultures: Check for bacterial infection in bloodstream.

  • HA1bc: Reflects average blood sugar levels over a 3-month period.

  • PSA: Screens for prostate cancer risk.

What do I need to do to prepare for a blood test?


  • Follow any instructions from your doctor about fasting or avoiding certain foods/medications before the test.

  • Drink extra water the day before to ensure good hydration.

  • Get a good night's sleep.

  • Consider applying a warm, moist towel to the arm where blood will be drawn to help dilate the veins.

  • Wear a short-sleeve shirt or something with sleeves that can be easily rolled up.

  • Avoid caffeinated beverages right before the test as they can dehydrate you.

  • Do light exercise like walking right before the test to increase blood flow.

What happens during the blood draw?


  1. You'll sit in a chair with your arm resting on an armrest or cushioned surface.

  2. The site where blood will be collected, usually the crease of your elbow, is cleaned with an antiseptic.

  3. An elastic band is wrapped around your upper arm to temporarily restrict blood flow and plump the vein.

  4. When the vein is visible, the phlebotomist (person drawing blood) inserts the needle and blood starts flowing into attached vials.

  5. When all needed samples are collected, the needle is removed and a cotton ball or gauze is placed over the site.

  6. You'll be asked to apply pressure on the site for a few minutes as the phlebotomist puts a bandage over it.

Does it hurt?


Some slight discomfort or a pinch may be felt when the needle goes in. Any pain typically lasts just seconds. Let the phlebotomist know if you feel significant pain so they can adjust the needle. Staying relaxed, looking away, and distracting yourself with conversation can help.

What happens after the blood test?


  • Rest for a few minutes before resuming normal activity. Keep the bandage on for the directed time.

  • Drink plenty of fluids and have a light snack to aid recovery.

  • Bruising, minor bleeding, or swelling may occur. Apply ice packs as needed.

  • Test results from routine blood work are usually available within a day or two. More complex tests require longer.

  • Your doctor will explain what the results mean, recommend any needed follow-up tests or treatment.

Blood tests provide valuable information about your health and enable early detection of many conditions when treatment is most effective. Understanding the process and preparing accordingly can help ease anxiety. Communicate any concerns with your healthcare provider so that getting blood drawn is as comfortable as possible.


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