Order Guide: Complete Blood Count (CBC)
If you are experiencing new-onset symptoms (symptoms lasting less than 3 months) or are unwell, we recommend seeking follow-up at an urgent care centre or walk-in clinic for assessment by a physician as your symptoms may be part of an acute illness that requires immediate intervention by a physician and may represent a life-threatening disease.

What is a Complete Blood Count (CBC)?

A complete blood count is the most commonly ordered blood test. It looks at three common cell types: red blood cells (carry oxygen), white blood cells (fight infections) and platelets (help the blood clot and prevent bleeding).

What does a CBC test include?

  • Hemoglobin: the amount of hemoglobin which is a protein that carries oxygen in your blood
  • Hematocrit: the amount of blood volume made up by red blood cells
  • RBC Count: the total count of red blood cells
  • MCV: the size of the red blood cell
  • MCHC: the average hemoglobin concentration inside a red blood cell
  • RDW: the average size differences between the smallest and largest red blood cells
  • WBC: the total number of white blood cells which includes: neutrophils, lymphocytes, monocytes, eosinophils, basophils
  • Platelets: the total number of platelets in the blood
  • MPV: the average size of platelets
  • Neutrophils: the total number of neutrophils (a type of white blood cell)
  • Monocytes: the total number of monocytes (a type of white blood cell)
  • Eosinophils: the total number of eosinophils (a type of white blood cell)
  • Basophils: the total number of basophils (a type of white blood cell)

What parts of the CBC are the most useful?

The most important parts of the CBC are:
  • Hemoglobin, Hematocrit, Total WBC and associated cell lines (i.e. Neutrophils, etc), Platelets and MCV. Doctors don’t often pay as much attention to the MPV, MCHC and RDW as they don’t guide medical decision-making as often as the other values do.

What’s the difference between diagnosis and screening?

Medical professionals arrange screening testing when they are looking to find problems in someone without symptoms. An example of a screening test would be a mammogram (breast x-ray), which is recommended for all women at age 50, even if they don’t have any breast symptoms. An example of a diagnostic test is a mammogram ordered for a woman who has felt a new breast lump, regardless of her age.

How often should I have a screening CBC?

There are no guidelines that recommend the frequency of a screening CBC. The standard of care practiced in Ontario is generally a CBC with annual or biennial (every 2 years) bloodwork starting at age 40. In many situations, for example, a doctor may order a CBC to investigate symptoms (i.e. fatigue, hair loss, heavy bleeding in women, vegan diet to assess nutritional status etc). Most physicians will order a CBC when they are investigating a patient with symptoms, as an abnormal CBC can quickly provide necessary information to guide further testing.

What can a CBC diagnose?

A CBC can be used to diagnose anemia, problems with your immune system, and identify liver disease, blood disorders and blood cancer.

What are the most common causes of anemia (low hemoglobin)?

  • Bleeding - the most commonly found cause of anemia is women of menstrual age who lose blood during their menstrual cycle
  • Iron deficiency - vegetarians, individuals with poor diet and heavy alcohol consumption can result in low iron stores which means the body doesn’t have enough building blocks to make hemoglobin
When should I NOT use TeleTest to order a CBC?
We advise consultation with a medical professional before ordering testing if you are having symptoms, to ensure your symptoms are not part of a life-threatening illness. Health care providers can quickly determine if your symptoms are part of a condition that requires immediate medical care that someone without medical training might not understand. Rarely, your symptoms can be part of a life-threatening illness best determined by a health care provider. Examples of when not to order a CBC include:
  • I am unwell, short of breath, experiencing chest pain or pressure, jaw pain, left arm pressure, palpitations, lightheaded, dizziness
  • I have a new-onset headache, dizziness, numbness or muscle weakness
  • I have difficulties swallowing, ringing in my ears
  • I have a new-onset rash
  • I am experiencing vomiting, diarrhea, or abdominal pain
  • I have a new respiratory infection (cough, runny nose, sore throat)
  • I have fevers or have experienced unintentional weight loss
  • I have rectal bleeding, have vomited up blood, or have black tarry stools
  • I have unexplained bruising, blood in my urine, or bleeding from my gums

What would be examples of when it would be appropriate to order a CBC?

  • I am screening as I am over the age of 40 and do not have a family doctor.
  • I am monitoring my hematocrit on Testosterone Replacement Therapy (TRT) or testosterone derivatives.
  • I have symptoms of fatigue that have lasted more than 3 months.
  • I am experiencing hair loss.
  • I am a vegetarian/vegan and want to ensure I don’t have anemia.
  • I am on a medication that requires regular monitoring of my CBC.

What affects CBC measurement?

If you have had a recent infection, are currently pregnant or dehydrated you can have abnormal cell counts. We recommend waiting 4 weeks after recovering from a recent infection before ordering a CBC. If you are currently pregnant, we do not recommend using TeleTest.

I have questions before ordering a test. Can TeleTest guide me?

If you require clarity before ordering testing, please reach out to us at [email protected] to discuss whether this is an appropriate test for you. You will be given the option to book an appointment with a doctor to book an assessment. If you cannot obtain an appointment with us in a timely fashion, please go to a local walk-in clinic or urgent care centre for assessment.

Is a CBC currently available as an insured test?

Currently, CBC is an uninsured test through TeleTest and is not covered by OHIP. If you would like to obtain a CBC as an insured test, you can head to a walk-in clinic for an assessment by a physician.