Blood Test

Last Reviewed: 25th April 2017.

What Is A Blood Test?

A blood test is the analysis of a blood sample from a patient to find naturally-occurring or foreign chemical or cellular components. 

A blood test can be done to analyze your blood for signs of problems, such as abnormal electrolyte balance, abnormal kidney function, abnormal liver functions, anaemia (lack of oxygen carrying red blood cells), low platelets, high amount of white blood cells, your blood type, the presence of drugs, and levels of different medications.

Today, blood tests can do many things, because doctors and scientists have identified many substances in the blood that can tell you if you have an infection, an autoimmune disease, a marker for cancer, inherited diseases, and even blood clots or heart failure. Blood tests are also used to tell your doctor if you are having a heart attack.

Blood is withdrawn from a vein in the arm, or by means of a prick to the finger.

Common Reasons For Blood Tests

If during the course of an examination your doctor uncovers an issue which may be indicative of a problem, your doctor may be able to find further information about your condition by taking a blood sample and testing it for certain substances. Symptoms that may prompt a blood test include:

  • Allergies
  • Fever
  • Weight loss
  • Jaundice (yellow color to skin and whites of the eyes)
  • Localized pain
  • Shortness of breath
  • Fatigue
  • Chest pain
  • Skin rash

Common things that your doctor or your healthcare practitioner would want to check for in your blood include:

  • Blood count for anemia (CBC)
  • White blood cell count
  • Platelet level
  • Stickiness of your blood or how thin your blood is
  • How well your blood clots
  • Your Kidney function
  • Liver Function
  • Bone profile
  • Crude evidence of infection or inflammation
  • How your immune cells are doing
  • Thyroid function
  • Blood sugar level (e.g to check for diabetes)
  • Normal bowel function e.g to check for pancreatitis or abnormal absorption of food like in celiac disease
  • Evidence of infection in your blood
  • Blood test for pregnancy
  • Test for evidence of cancer
  • Prostate test
  • Presence of abnormal levels of drugs or chemicals
  • Check for overdose
  • Check for inherited disease
  • Heart attack 
  • Blood group
  • Hormone level - e.g to confirm menopause or whether you are ovulating
  • For evidence of allergy
  • To unravel unexplained weight loss
  • Confirm or exclude heart failure
  • Look for  and identify bugs or parasites in the body or blood.

Common Blood Tests And What They Mean

The following are the common blood tests and what they mean:

Full Blood Count (FBC) or Complete Blood Count (CBC)

This is a blood test to check your blood count. This is perhaps one of the most commonly-used blood tests in the world.

In the UK and many part of the English-speaking world, it is referred to as Full Blood Count or FBC. In North America, it is referred to as the Complete Blood count.

This test checks for:

Haemoglobin Level

Haemoglobin (Hb) is the substance in the blood that gives it the red colour. It is what carries oxygen in the blood to the body tissue and it is made from iron and protein. Normal hemoglobin level is about 12 to 16 in women and 14 to 18 in men. Low levels below 10 in anybody is referred to as anaemia, or shortage of red blood cells.

White Blood Count or WBC

White blood cells, if they are increased, can be an indicator of infection, or even types of leukemia. They are the cells your body normally produces in your bone marrow to protect you against infection. Normal levels of white blood cells in an adult Caucasian is 4000 to 11000 per dl and 2,500 to 8,500 in people of Afro-Caribbean descent.

Platelet Count

Platelets are the cells that form clots and help your body heal bleeding wounds by sticking together and forming a plug. However, platelets can also clog your blood vessels if they are narrowed by atherosclerotic heart disease, for example. A big clot will obstruct the blood vessels.

For this blood test, blood will be drawn from the vein in your arm and siphoned into a special tube for laboratory testing. The blood is tested for hemoglobin levels in the red blood cells, which can help your doctor if you have anaemia caused by iron deficiency. Iron produces the molecule heme, which carries oxygen in the red blood cells throughout your body to your tissues. 

When your blood goes through the centrifuge, a spinner, the blood cells spin to the bottom to make a sediment, and the clear liquid on top is called plasma. The laboratory technicians will put the sediment under a microscope and will examine it and count how many red blood cells, white blood cells, and platelets are in the sediment per square millimeter.


  • MCV
  • MCHC
  • WBC

Normal Range in Health

  • 137 - 180 (Females 120 - 150)
  • 0.40 - 0.54
  • 82 - 100
  • 320 - 360
  • 150 - 400
  • 4.0 - 11.0 Whites (2 - 8.5 Blacks)
  • 2.0 - 8.0
  • 0.7 - 3.5
  • 0.0 - 1.0
  • 0.0 - 0.7
  • 0.0 - 0.2

Electrolytes And Urea Levels

Your body’s cells need certain molecules called electrolytes, to function. These are also referred to as blood salts. They include:

  • Sodium (Na)
  • Chloride (Cl-)
  • Potassium (K) 
  • Bicarbonate molecules (HCO3)
  • Calcium
  • Magnesium
  • Phosphate
  • Urea
  • Urate or uric acid

These are also referred to DAX or blood urea nitrogen and electrolytes. They are required for the maintenance of electrical balance in your body, transmission of nerve impulses, blood pressure control, water balance and more.

Depletion of your blood salts or electrolytes could lead to:

  • Confusion
  • Low blood pressure
  • Vomiting
  • Swollen legs and ankles
  • Abdominal distension
  • Gout

Any abnormality in the natural level and balance of these chemicals could lead to illness. Illnesses like diarrhoea and vomiting can also lead to excessive loss of these chemicals. 

There are many reasons that your body has been unable to keep your electrolytes balanced, and one reason may be problems with your kidneys, which help control the excretion and balance of these elements. Kidney disease may keep you from having the right amounts of electrolytes for your cells to function.

Some drugs can also cause imbalances of electrolytes, which can be more dangerous than we think. As an example, executions in the United States call for a "lethal injection" that contains excess potassium because large amounts of potassium can stop the heart.   



Normal Range in Health

  • 133-145 mmol/L
  • 3.3-5.1 mmol/L
  • 98-111 mmol/L
  • 2.10-2.55 mmol/L

Kidney Functions

Whether abdominal pain or another condition, an imbalance of fluids and electrolytes, can lead to kidney problems. Kidney problems are diagnosed using a kidney function test, which is among the top blood tests administered to diagnose conditions.


  • UREA

Normal Range in Health

  •  50-120 umol/L
  •  3.0-9.0 mmol/L
  • 210-490 umol/L
  • >=60 mL/min/1.73m2

Liver Function test

Your liver is the site of many activities:

  • It stores carbohydrates to be made into sugar later, when you are not eating.
  • It produces bile, which helps you digest your food. 
  • Liver enzymes break down chemicals and drugs.

Testing for liver function is a frequently requested blood test for abdominal pain amongst other conditions.



Normal Range in Health

  • 1-60 U/L
  • 33-48 g/L
  • 30-145 U/L
  • 11-63

Fatty liver disease, excessive alcohol intake, metabolic syndrome, drugs like statins are all common causes of elevated liver function test, especially the GGT.

Indicators of Inflammation

There are some chemicals in your blood that are released by damaged or injured cells. Such injury could be from infection, trauma, problems with the immune system, or even cancer. In many conditions that causes abdominal pain, important inflammatory markers or indicators of inflammation often tested in the blood include:

CRP (Cryo-Reactive Protein)

CRP is a protein produced by the liver in response to inflammation - be it from infection or any other causes of inflammation. A normal level of CRP is between zero (0) to Eight (8). Levels higher than 10 indicate an ongoing acute inflammation.

ESR (Erythrocyte Sedimentation Rate)

ESR is another marker of inflammation often checked in the blood. ESR could be raised in chronic inflammation too as in acute inflammation. 

Tumor Markers

Cancer cells sometimes release special chemicals into the bloodstream, like prostate-specific-antigen (PSA), which can be used to help your doctor make a cancer diagnosis. Tumour markers are substances found in abnormal quantity, usually when there is the presence of a type of tumor or cancer in the body.

Though a high amount of any of these chemicals is likely to indicate the presence of a tumour,  they generally tend to have low level of accuracy in predicting the presence of cancers.

Tumor markers are best used to track recovery or recurrence in patients already diagnosed with a known cancer.

Common tumour markers requested in blood test include:

  • Prostate Specific Antigen (PSA)
  • Alpha Feto-Protein
  • Cancer Antigen 125 (Ca 125)
  • Carbohydrate Antigen 19-9 (Ca 19-9)
  • Carcinoembryonic Antigen (CEA)
empty blood vial

Other Blood Tests

Every month, researchers are finding more chemicals in the blood to analyze to help your doctor make a diagnosis. Because a blood test is pretty simple to do, it is useful to be able to understand the purpose of all the chemicals in the blood.

Common and important blood tests that may be helpful in the diagnosis of abdominal pain and other related conditions include:

  • Albumin Level
  • Aldolase
  • Aldosterone Levels(Serum)
  • Alkaline Phosphatase
  • Alpha-1 Antitrypsin
  • ALT (SGPT)
  • Ammonia Blood Test
  • Amylase
  • Antinuclear Antibody Test (ANA)
  • Antistreptolysin O Antibody (ASO)
  • Ascaris Antibodies, IgE
  • AST (SGOT)
  • Babesia PCR
  • Blood Group (Blood Type) Test
  • BUN and Creatinine
  • CA 19-9 Pancreas Carbohydrate Antigen
  • Calcium Blood Test
  • Candida Albicans Antigen Test
  • Carcinoembryonic Antigen
  • Celiac screen - TTG
  • Ceruloplasmin (CER)
  • Cholesterol Panel
  • Cholinesterase Test
  • Chromogranin A
  • Clostridium difficile Toxins A & B
  • Coccidioides Antibodies
  • Complement C1 Esterase Inhibitor
  • Complement, Total (CH50)
  • Complete Blood Count (CBC) + Differential + Platelets
  • Comprehensive Digestive Stool Analysis 2.0 (CDSA)
  • Cortisol Level (Diurnal)
  • Creatine Kinase (CK)
  • Cytomegalovirus (CMV) Test
  • DNA Stool Test
  • Endomysial Antibody
  • Erythrocyte Sedimentation Rate (ESR)
  • Estradiol (E2)
  • Ferritin
  • Folate (Folic Acid) Levels
  • Follicle Stimulating Hormone (FSH)
  • Food Allergy Test
  • Glucose Blood Test
  • GGT Test
  • Glutathione Test
  • Growth Hormone, RIA
  • H. Pylori Blood Test
  • Hemochromatosis Genetic DNA Test
  • Hepatitis A Test
  • Hepatitis B Test
  • Hepatitis C Test
  • Hepatitis C Virus (HCV) Real Time PCR (Viral Load)
  • Herpes Varicella Zoster, IgG (Chicken Pox)
  • Homocysteine Test
  • Immunoglobulins
  • Iron Level
  • Kidney Function Test
  • Lactate Dehydrogenase
  • LH (Luteinizing Hormone)
  • Liver Function Test
  • Lupus Anticoagulant (PTT-LA)
  • Lyme Disease Test (Serology)
  • Magnesium Level
  • Mercury Level (Serum)
  • Mitochondrial (M2) Antibody
  • Mold Test
  • Phosphorus (Serum)
  • Potassium
  • Progesterone Test
  • Protein Electrophoresis (Serum)
  • Rheumatoid Arthritis Factor
  • Reticulocyte Count
  • Reverse T3 Test
  • Rocky Mountain Spotted Fever Screen
  • Testosterone Levels
  • Total Iron Binding Capacity (TIBC)
  • Transferritin
  • Thyroid Function Test
  • Toxic Heavy Metals
  • Troponin I
  • Zinc

Most people don’t know you can order most blood tests online yourself, without a medical degree and without a prescription. Go to the True Health Labs (affiliate links) and see what tests they currently have available and order your test. Yes, you can be in control of what you want tested. 


  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.