Complete Blood Count (CBC)#

Yes - low hemoglobin defines anemia. The most common causes:

• Bleeding: in women of menstruating age, the most common cause is menstrual blood loss. In adults of any age, slow bleeding from the gut (ulcers, polyps, hemorrhoids) is another common cause.
• Iron deficiency: vegetarian or vegan diet, heavy alcohol use, poor absorption (celiac disease, inflammatory bowel disease), or chronic bleeding.
• B12 or folate deficiency: vegan diet, certain stomach surgeries, autoimmune conditions, some medications (long-term acid-suppressing medications, some first-line oral diabetes medications).
• Chronic disease: kidney disease, inflammation, thyroid disease.
• Inherited: thalassemia trait (common in people of Mediterranean, South Asian, Southeast Asian, and African descent), sickle cell trait or disease.

The MCV helps narrow down the cause:

• Low MCV (small red cells): usually iron deficiency or thalassemia.
• High MCV (large red cells): usually B12 deficiency, folate deficiency, alcohol, hypothyroidism, or some medications.
• Normal MCV: blood loss, chronic disease, kidney disease, mixed deficiency.

Your clinician will often order follow-up tests (ferritin, B12, folate, thyroid) based on the MCV.

Usually no. Clinicians rarely focus on MCHC, MCH, or RDW in isolation. The values that matter most are hemoglobin, hematocrit, and MCV.

• MCHC (Mean Corpuscular Hemoglobin Concentration) and MCH (Mean Corpuscular Hemoglobin) tend to track with hemoglobin and MCV. If those are normal, a minor MCHC or MCH flag is almost always a harmless lab artifact.
• RDW (Red cell Distribution Width) can be elevated in mixed nutritional deficiencies or in early anemia, but an isolated mildly high RDW with normal hemoglobin and MCV usually does not need follow-up.

An isolated MCHC, MCH, or RDW flag typically does not need repeat testing unless your hemoglobin or MCV is also abnormal or you have symptoms.

A high WBC count (leukocytosis) most often reflects:

• Active infection - bacterial infections especially raise neutrophils.
• Recent illness or stress - WBC can remain elevated for 1 to 2 weeks after.
• Steroid pills (prescription corticosteroids) can raise WBC.
• Pregnancy - mild WBC elevation is normal.
• Smoking - chronic smokers often run higher WBC.
• Rarely: blood disorders or blood cancers, especially if WBC is very high (above 30) or the differential shows abnormal cell populations.

A mildly elevated WBC after a recent cold or infection usually returns to normal within a few weeks. If WBC is significantly elevated, persistent, or paired with other abnormalities, your clinician will arrange further testing.

A low WBC (leukopenia) can be caused by:

• Recent viral infection - viruses can suppress WBC for 1 to 4 weeks.
• Some prescription medications - certain blood pressure medications, anti-seizure medications, anti-thyroid medications, chemotherapy.
• Autoimmune conditions - lupus, rheumatoid arthritis.
• B12 or folate deficiency - same nutritional deficiencies that cause anemia can lower WBC.
• Some ethnic backgrounds: people of African descent often have a naturally lower neutrophil count (called "benign ethnic neutropenia") and this is a healthy variation, not a problem.
• Bone marrow problems - rare, but possible with persistent significant leukopenia.

A mildly low WBC after a recent illness or in someone known to have benign ethnic neutropenia usually does not need workup. Persistent or significantly low neutrophils (below 1.0) warrant further investigation - please see a clinician.

Mildly low platelets (130 to 150) often have no specific cause and may simply be your baseline. Possible causes of lower platelets include:

• Recent viral illness
• Pregnancy (mild platelet drop is normal)
• Heavy alcohol use
• Certain medications (some antibiotics, some anti-seizure medications, some prescription heartburn medications)
• Autoimmune conditions (ITP)
• Liver disease
• Vitamin B12 or folate deficiency

Platelets below 100 generally warrant follow-up. Platelets below 50 with bleeding or bruising are a medical urgency - please go to urgent care or the emergency department.

A mildly high platelet count (above 400) is common and most often reflects:

• Recent illness, infection, or inflammation - platelets are also "acute phase reactants" and rise with stress.
• Iron deficiency
• Recovery from blood loss or surgery
• Smoking

Significantly elevated platelets (above 600 to 800) that persist warrant further evaluation. If you have new headaches, numbness, chest pain, or shortness of breath alongside high platelets, please see a clinician in person.

• Screening is testing in someone with no symptoms, looking for problems before they cause trouble. A screening CBC at age 40 is an example.
• Diagnostic testing is ordered to investigate symptoms. Ordering a CBC because someone has fatigue, hair loss, or heavy periods is diagnostic, not screening.

The same blood test can be either, depending on why it is ordered. Provincial health plans cover diagnostic CBC fully; screening CBC may or may not be covered depending on age and risk factors.

Some long-standing health conditions - inflammation, autoimmune disease, kidney disease, certain cancers - cause a low-grade anemia even when iron, B12, and folate stores are normal. The body's inflammatory signals reduce red blood cell production. Treating the underlying condition usually improves the anemia.

Not always. A higher than expected hemoglobin can reflect:

• Dehydration - the blood is concentrated. Re-hydrate and retest.
• Smoking and chronic lung disease - the body produces more red cells to compensate for lower oxygen.
• Living at high altitude.
• Sleep apnea.
• Testosterone or anabolic steroids - one of the most common reasons we see elevated hemoglobin and hematocrit in TRT monitoring.
• Polycythemia vera - a bone-marrow disorder. Less common, but important to rule out when hemoglobin is significantly elevated and the cause is not obvious.

Hematocrit above 54% generally warrants follow-up. Hematocrit above 60% is significant and needs prompt clinical assessment.

Standard cadence for monitoring on TRT:

• Baseline before starting
• 3 to 6 months after starting or changing dose
• Then every 12 months once stable

We are looking for hematocrit (Hct). Rising Hct above 54% is the most common reason we adjust TRT dose or recommend a temporary pause. See the TRT pages for more.

A CBC plus vitamin B12, ferritin (the iron-storage protein), and folate is a reasonable nutritional screening every 1 to 2 years for vegetarians and vegans, especially if you have not been taking a B12 supplement. Plant-based diets are healthy but require either fortified foods or a B12 supplement to avoid long-term deficiency.

• Recent infection - WBC and platelets often elevated; can take 2 to 4 weeks to normalize.
• Dehydration - all cell concentrations falsely elevated.
• Pregnancy - hemoglobin is naturally lower, WBC slightly higher.
• Recent strenuous exercise - WBC briefly elevated.
• Sample handling and timing - small variations are normal between draws.

For screening, we recommend waiting at least 4 weeks after an acute illness and being well-hydrated on the day of the draw.

There is no Canadian guideline that strictly defines screening CBC frequency. Common practice:

• Once at baseline if you are over 40 and have not had bloodwork before
• Every 1 to 2 years from age 40 if you have risk factors
• More often if monitoring a specific condition (TRT, vegan diet, heavy menstrual periods, on a medication that affects blood counts)

If your CBC is normal and you have no risk factors, you do not need yearly testing.

Currently, a stand-alone screening CBC is generally not insured under provincial health plans. If you want a CBC as an insured test, see a clinician in person at a walk-in or family-doctor visit who can document symptoms or risk factors that meet provincial coverage criteria.

TeleTest can arrange a CBC as a self-pay test through our partner labs.

If you are unsure whether a CBC is appropriate for you, please reach out via our contact form. We can help you decide whether a CBC fits your situation, or whether you should see a clinician in person first.