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Complete blood count (CBC)

Updated 2026-10-14Written for education by the Zenlo Health editorial teamHow we review
Quick answerA complete blood count (CBC) counts your red blood cells, white blood cells, and platelets and measures hemoglobin. It helps screen for anemia, infection, and clotting or bone marrow problems.
Fasting and prepNo fasting needed.
Typical turnaroundUsually 1 day.
Also calledcbc, cbc with differential

What it measures

Low hemoglobin points to anemia, and the red cell size (MCV) hints at the cause, such as iron or B12 deficiency. A high white cell count often reflects infection or inflammation. Platelets help blood clot.

Who should consider it

  • Anyone feeling unusually tired or weak
  • People with heavy periods or a history of anemia
  • Adults wanting a routine baseline

How to read your result

  • Reference ranges differ by lab, age, and sex. Use the range printed on your report.
  • Low hemoglobin with a low MCV often points toward iron deficiency. Ferritin helps confirm.
  • Mild changes can be normal for you. Trends matter more than one number.

Reference ranges differ between labs. Use the range printed on your own report.

What to do next

If hemoglobin is low, ferritin and B12 are the usual next tests.

Where to order Complete blood count

These sellers include an independent physician order. You pay online and visit a partner lab. Availability, price, and lab network vary, so confirm at checkout.

Private MD Labs

Online lab seller
  • Says 4,500+ Quest and Labcorp locations
  • Every order reviewed by a physician. Says you pay $1 to start and the rest after results.
  • Secure online portal with plain-English explanations. Says many results arrive overnight.
Visit site Read review

HealthLabs

Online lab seller
  • Says 4,500+ labs, including Quest and Labcorp
  • Online or by phone. No doctor referral or insurance needed.
  • Secure HealthLabs account. Says 1 to 3 business days.
Visit site Read review

Walk-In Lab

Online lab seller
  • Lab network not named on its homepage
  • Online, no insurance or doctor order needed. Shows a $6 physician fee per order on popular tests.
  • Online account. Turnaround not stated on its homepage.
Visit site Read review

Quest Health

Lab-run
  • Quest, 2,000+ locations
  • Buy online and book a Quest appointment. An independent provider is involved.
  • Online as soon as ready, with an email alert. Provider discussion included at no extra cost.
Visit site Read review

Seller details come from each seller's own site and can change. Confirm price, lab location, and state availability at checkout.

Questions people ask

Do I need to fast for a CBC?

No. You can eat and drink normally unless you are combining it with a fasting test.

What does a high white blood cell count mean?

Infection, stress, steroid use, and inflammation are common causes. Persistent or very high counts need a clinician.

Related guides

Ferritin

Shows your body's iron stores.

Read

Vitamin B12

Checks B12 for fatigue, tingling, and anemia questions.

Read

Annual physical blood work

A solid baseline: CBC, CMP, lipids, A1C, and thyroid.

Read

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