Blood Test for Cancer: Can Blood Tests Detect Cancer?

By Dr. Amit Kumar in Cancer Care

Mar 20, 2025

Blood tests serve as valuable tools in cancer detection, though they cannot independently confirm most cancer diagnoses. These tests form part of a broader diagnostic approach, working alongside other medical examinations to identify potential malignancies.

A groundbreaking 2024 research study reveals that cancer can be detected by blood test with remarkable accuracy, identifying 93% of Stage I cancers in males and 84% in females across 18 different cancer types. This scientific advancement marks a significant milestone in cancer detection capabilities.

Blood testing serves various purposes in cancer diagnosis, from detecting blood cancers like leukaemia and lymphoma to monitoring specific tumour markers such as PSA for prostate cancer and CA-125 for ovarian cancer. Blood work also plays a key role in monitoring cancer treatment effectiveness and detecting potential recurrence. Regular testing helps create a baseline for overall health, enabling doctors to identify concerning changes early 2. This comprehensive guide explores the capabilities and limitations of blood tests for cancer patients, helping readers understand when and how these tests can be most effective.

Types of Blood Tests for Cancer Diagnosis

Doctors employ four distinct categories of blood tests to detect and monitor cancer. Each type serves unique purposes in cancer diagnosis and treatment monitoring.

Complete Blood Count (CBC): This fundamental test measures various blood components. It analyses red blood cells, white blood cells, and platelets, alongside haemoglobin and hematocrit levels. However, CBC helps detect blood cancers like leukaemia and lymphoma, yet it cannot identify solid organ cancers like lung, breast, or colon cancers.

Tumour Marker Blood Tests: These tests identify specific chemicals released into the bloodstream. The CA-125 blood test is a common tumour marker test that aids in planning treatment and checking for the recurrence of ovarian and pancreatic cancers.

PSA Test: The PSA test examines prostate-specific antigen levels, where elevated readings might indicate prostate cancer.

Blood Protein Tests: These tests examine abnormal protein levels that could indicate certain types of cancer, primarily blood cancers like leukaemia, lymphoma, and multiple myeloma. Blood protein tests often form part of a comprehensive metabolic panel, providing crucial information about protein levels.

Circulating Tumour Cell (CTC) Tests: CTC tests are a sophisticated form of liquid biopsy. They detect tiny pieces of tumours that break off and travel through the bloodstream. Doctors use CTC tests to predict outcomes in people with metastatic breast, prostate, or colon cancers. Indeed, a low level of CTCs indicates a favourable outcome, whereas numerous CTCs might suggest the need for additional treatment.

Beyond these primary categories, emerging technologies continue enhancing cancer detection through blood tests:

The Galleri test, a sophisticated screening tool, can detect signals for multiple cancer types through a simple blood draw. This test mainly benefits adults aged 50 and above, who face 13 times higher cancer risk compared to younger individuals 7.
A proteomics-based plasma test has shown remarkable potential in early cancer detection. Research indicates this test successfully identified 93% of Stage I cancers in males and 84% of Stage I cancers in females across 18 different cancer types 3.

Circulating tumour DNA (ctDNA) detection tests detect tiny fragments of tumour DNA in the blood. Research indicates that ctDNA detection rates correlate with cancer stages, showing 47%, 55%, 69% and 82% detection rates for stages I, II, III and IV cancers, respectively.

Dependencies on Other Diagnostic Modalities

Doctors rely on multiple diagnostic methods alongside blood tests for accurate cancer detection. Despite advancements in blood-based screening, no single test definitively confirms cancer presence without additional verification.

For optimal cancer detection, blood tests work in conjunction with:

Biopsies for tissue analysis
Imaging tests, including X-rays, CT scans, MRI scans, ultrasounds, bone scans, and PET scans
Specialised screening tests like mammograms for breast cancer, Pap smears to identify cervical cancer, and colonoscopies to detect colorectal cancer.
Myelograms assist in identifying spinal cord tumours, while bronchoscopies help diagnose lung cancer.

Biopsies remain crucial in cancer diagnosis. These procedures involve extracting tissue samples from organs or bone marrow for laboratory analysis. Standard biopsy types encompass:

Bone marrow biopsies
Endoscopic biopsies
Skin biopsies
Needle biopsies

Laboratory analysis extends beyond blood examination. Chemical processes determine levels of various components in bodily fluids and tissues 1. Doctors assess:

Electrolyte levels
Blood glucose
Enzyme activity
Hormone levels
Protein concentrations

Current research indicates promising developments in blood-based cancer screening. Nevertheless, nearly 60% of cancer-related deaths occur due to cancers lacking established screening tests. Blood tests might eventually replace expensive imaging procedures, reduce radiation exposure from image-based screening, and eliminate certain invasive procedures.

Doctors consider each patient's specific situation for optimal diagnosis. Blood test results require careful interpretation, and implications for further testing must be discussed with qualified doctors.

Conclusion

Blood tests for cancer have proven their worth as essential tools in cancer detection, though they work best alongside other diagnostic methods. Recent developments, particularly the Galleri test and proteomics-based plasma testing, show remarkable promise, with detection rates above 80% for early-stage cancers.

Doctors now effectively use various blood tests, from Complete blood count tests that detect blood cancers to sophisticated Circulating tumour cell tests that track cancer spread. These tests offer significant advantages over traditional methods, requiring only small blood samples while providing valuable insights.

Despite these advancements, doctors still rely on a combination of diagnostic tools for accurate cancer detection. Blood tests work together with imaging techniques, biopsies, and specialised screening methods to create a complete diagnostic picture. This comprehensive approach helps doctors make informed decisions about treatment paths and monitoring strategies.

The future looks promising as blood-based cancer detection continues to advance. These developments could reduce the need for invasive procedures and expensive imaging tests, making cancer screening more accessible and comfortable for patients. Still, patients should remember that blood test results need careful interpretation by qualified doctors who can determine the next steps in their diagnostic journey.

FAQs

Does a normal blood test rule out cancer?

Normal blood test results do not guarantee the absence of cancer. Most types of cancer cannot be detected through blood work alone, except for certain blood cancers like leukaemia, lymphoma, and multiple myeloma

What are common blood tests used for cancer detection?

Tests like tumour markers, complete blood count (CBC), circulating tumour DNA (ctDNA), and liquid biopsy can help detect and monitor cancer.

How accurate are blood tests for diagnosing cancer?

While some blood tests provide useful indicators, they are not always definitive. Additional tests, such as biopsies and scans, are often needed for cancer confirmation.

Can blood tests detect cancer in the early stages?

Some tests, like ctDNA and tumour markers, can indicate cancer in its early stages, but they are not always conclusive and require further diagnostic procedures.