CBC Tests and Cancer: What Doctors Look For In Your Results

November 18, 2024

Medically reviewed by Dr. Doug Blayney on November 18, 2024.

Introduction

A complete blood count (CBC) is a common blood test that provides insight into aspects of your overall health. Doctors often recommend CBC tests as part of routine health screenings or during the initial stages of cancer diagnosis and treatment..

While a CBC test alone can't confirm cancer, it can reveal important clues that prompt further investigation. By understanding what a CBC measures and how those markers can indicate potential cancer, you can be a more informed patient and work closely with your doctor.

Want more information about cancer testing? Want to connect with support to help you through the cancer experience? Click here to learn more about Your Cancer GPS™, our step-by-step guide to help you navigate the cancer experience and find the support your need from diagnosis to living with “the new normal” after treatment. Learn more here.

What Does a CBC Test Measure?

A standard CBC test checks the levels of the following components in your blood:

Red Blood Cells (RBCs): These cells carry oxygen throughout your body. Low RBC counts can signal anemia.
White Blood Cells (WBCs): These cells help fight infection. High or low WBC levels may indicate an underlying condition. There are several types of WBCs including leukocytes, lymphocytes, monocytes, eosinophils, and others.
Hemoglobin: This iron-rich protein in RBCs transports oxygen. Low hemoglobin levels can also point to anemia.
Hematocrit: This measures the percentage of RBCs in your blood. It's tested alongside hemoglobin.
Platelets: These cells help your blood clot. Abnormal platelet counts can signal a problem.

Doctors use these measurements to get a broad picture of your overall health. Significant imbalances in any of these areas can provide important clues during cancer screening and diagnosis.

How Can a CBC Test Indicate Cancer?

While a CBC test can't definitively diagnose cancer, abnormal results may prompt further investigation. Here are some ways CBC irregularities can signal potential cancer:

High White Blood Cell Count: An elevated WBC count could indicate an infection, inflammatory condition, or rarely, blood cancer like leukemia.
Low Red Blood Cell/Hemoglobin Count: Anemia, or low RBC/hemoglobin levels, is common in many types of cancer that affect blood cell production, like lymphoma or multiple myeloma, but are much more common when people are deficient in iron, or have a disease other than cancer.
Platelet Abnormalities: Both high and low platelet counts have been linked to certain cancers that impact the bone marrow, such as leukemia or metastatic solid tumors.

The key is that these CBC irregularities don't automatically mean cancer. They simply raise a flag that something unusual is occurring in the body and warrants further investigation.

Markers Doctors Focus On In CBC Tests for Cancer

When reviewing your CBC results, doctors pay close attention to the following markers that may indicate cancer:

High White Blood Cell (WBC) Count: This could signal an infection, inflammation, or a blood cancer like leukemia.
Low Red Blood Cell (RBC) Count or Hemoglobin Levels: Anemia is common in lymphoma, multiple myeloma, and other cancers that affect blood cell production.
Abnormal Platelet Counts: Both high and low platelet levels have been linked to bone marrow disorders and certain solid tumor cancers.

These CBC irregularities don't confirm cancer on their own. But they provide important clues that prompt additional testing.

Conditions Often Detected or Indicated by CBC in Cancer Patients

Certain cancer types are more likely to show up in abnormal CBC results compared to others:

Blood Cancers: Conditions like leukemia, lymphoma, and multiple myeloma often cause noticeable changes in WBC, RBC, and platelet counts.
Solid Tumors: While less common, some solid cancers that spread to the bone marrow or affect blood cell production can also impact CBC markers.
During chemotherapy: CBC levels are rapidly changing, and may signal the need to adjust the chemotherapy doses or schedule, add supportive care medications, or rarely, to administer blood or platelet transfusions. Again, ask your treatment team.

For example, low RBC and hemoglobin levels may signal anemia, which can occur in many types of cancer. Conversely, high WBC counts are a hallmark sign of leukemia.

Interpreting Your CBC Test Results: What Patients Should Know

Reviewing your CBC report can feel overwhelming, but there are a few key things to focus on:

Look for any measurements outside the normal range, whether high or low.
Don't panic if one or two components are slightly off - minor imbalances are common.
Pay close attention to significant abnormalities, as these are more likely to signal an underlying issue.
Measurements of red blood cell size (MCV – mean corpuscular volume and RDW – red cell distribution width), hemoglobin levels (MHC – mean hemoglobin concentration and MCHC – mean corpuscular hemoglobin concentration) are very often slightly abnormal and are of almost no significance.

It's important to discuss your CBC results with your doctor. They can provide a full interpretation and determine if follow-up tests or monitoring are needed. Don't try to diagnose yourself based on the CBC alone.

Additional Insights on CBC and Cancer Detection

While the CBC test is a valuable screening tool, it's not the only way doctors detect and monitor cancer. Here are some additional insights to keep in mind:

Specialized Cancer Blood Tests: In addition to the standard CBC, doctors may order more targeted blood tests that look for specific cancer biomarkers or tumor markers. These can provide more definitive indications of certain cancer types. (Read more about biomarker testing here.)
Imaging Tests: Techniques like CT scans, MRIs, and PET scans allow doctors to visualize tumors and other abnormalities that may not be detected through blood work alone.
Biopsy: When cancer is suspected, a small sample of tissue is often taken and examined under a microscope to confirm the diagnosis.
Ongoing Monitoring: For those diagnosed with cancer, regular CBC tests and other blood work are crucial for tracking the disease's progression and response to treatment.

While the CBC is a helpful starting point, it's just one piece of the cancer detection and management puzzle. Working closely with your medical team is key to fully understanding your results and next steps.

Join a community of people who “get it”

The Manta Cares team is composed of cancer survivors, caregivers, oncologists and nurses - so we truly understand the challenges that come with a cancer diagnosis because we’ve been there. We are here to walk with you as you go through your own cancer experience. Please don’t hesitate to reach out with any questions. We have even developed Your Cancer GPS™, a platform with disease-specific step-by-step maps to show you all the paths you might face during your cancer experience, future treatment options and connect you with relevant support and resources. Sign up for access to the Your Cancer GPS™ platform here.

Be sure to subscribe to our newsletter and check out our free resources like our Chemotherapy Checklist for Caregivers, Financial Checklist for Cancer Treatment and more. We also put out a bi-weekly podcast called the Patient from Hell to educate, empower and hopefully inspire you as you go through this crappy experience. You can listen on Spotify, Apple Podcasts, YouTube or anywhere you listen to podcasts. Dealing with cancer as a patient or caregiver can feel really lonely. Just know that you are not alone in this experience.

Conclusion

A CBC test is a valuable screening tool that can reveal important clues about your overall health, including potential signs of cancer. While abnormal results don't automatically mean cancer, they do warrant further investigation.

By understanding what a CBC measures and how those markers can indicate cancer, you can work closely with your doctor to stay on top of your health. Remember, a CBC alone can't confirm or rule out cancer - it's just one piece of the puzzle. Rely on your medical team to guide you through the process and provide a comprehensive evaluation.

Staying informed and advocating for your care are important, but try not to worry excessively about every minor fluctuation in your CBC (easier said than done, we know!). Focus on communicating openly with your doctor and following their recommendations for any additional testing or monitoring. With their expertise and your active participation, you can ensure your health concerns are thoroughly addressed.

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FAQs About CBC Tests

Q: Can CBC detect any disease?

Ans - A CBC (Complete Blood Count) can show changes in your blood that may suggest infections, anemia, or some cancers, but it doesn’t detect every disease.

Q: What cancers don't show up in blood work?

Ans - Some cancers, like early-stage breast, lung, or skin cancers, may not show up in blood tests.

Q: What is the biggest indicator of cancer?

Ans - The biggest sign of cancer is usually a lump, unusual bleeding, or changes in your body that don’t go away.

Q: How to confirm skin cancer?

Ans - Doctors confirm skin cancer by looking at the skin and doing a biopsy, which means testing a small piece of the skin.

Q: How to detect cancer early?

Ans - Cancer can be detected early through regular checkups, screenings, and paying attention to unusual symptoms.

Q: How do doctors confirm cancer?

Ans - Doctors confirm cancer by doing tests like biopsies, imaging scans (like MRIs), and blood tests.

Q: What are 20 warning signs of cancer?

Ans - Some warning signs include lumps, weight loss, fatigue, pain, unusual bleeding, skin changes, and persistent cough, but there are many more.

Q: What is the signature test for cancer?

Ans - There isn’t one single test; the test depends on the type of cancer, like mammograms for breast cancer or colonoscopies for colon cancer.

Q: What do doctors look for in a CBC?

Ans - In a CBC, doctors check for unusual blood cell counts or sizes that could suggest problems like anemia or leukemia.

Q: Can a CBC blood test detect skin cancer?

Ans - A CBC cannot detect skin cancer, but it might show changes if the cancer has spread.

Q: Which test detects cancer?

Ans - Tests like biopsies, imaging scans, and specific screenings (like Pap smears or colonoscopies) are used to detect cancer.

Disclaimer: All content and information provided in connection with Manta Cares is solely intended for informational and educational purposes only. This content and information is not intended to be a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

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