Can a blood test diagnose melanoma?

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While blood tests can help guide treatment, doctors do not use them to diagnose melanoma.

Circulating tumor cell (CTC) tests can identify some cancers, but inconsistent results and low sensitivity make this test unsuitable for diagnosing melanoma.

Melanoma diagnostic tests include:

• Medical history: Doctors ask for information, such as whether a person has had risk factors, which may include tanning bed exposure or whether anyone in their family has had skin cancer.
• Physical exam: Doctors check for lymph node swelling and the appearance and locations of skin cancer lesions.
• Dermoscopy: Doctors use a dermatoscope to obtain a close-up view of skin lesions and take digital images to track skin changes.
• Reflectance confocal microscopy (RCM): Doctors use a laser and microscope to create detailed 3D images of skin lesions.
• Spectroscopic devices: These assess skin by analyzing energy and wavelengths of light.
• Adhesive patch testing: Doctors use a sticky patch to remove surface skin cells for testing.
• Skin biopsy: A biopsy involves removing a tissue sample for lab testing. There are several types, including deep shave, punch, fine needle, incisional, and excisional. Doctors take samples from cancerous lesions, as well as from lymph nodes if a doctor suspects the melanoma may have spread.
• Lab testing: Pathologists examine biopsy samples using microscopes. If they cannot visually diagnose cancer, they may conduct lab tests on the samples.
• Imaging tests: These tests allow doctors to see inside the body for spreading cancer. Types of imaging tests include:
  • X-rays
  • ultrasound
  • CT scans
  • MRI scans
  • PET scans

Blood tests help doctors in several ways when they treat people with cancer.

The blood sample information helps doctors monitor cancer progression and guides their treatment decisions.

Blood tests can also indicate how well a person’s organs are functioning and whether they can undergo certain tests and procedures.

Test results provide doctors with important information.

Blood serum markers

Doctors test a person’s lactate dehydrogenase (LDH) blood levels to monitor their melanoma if the doctor suspects it is advanced. High blood levels of LDH can mean a melanoma is more advanced and may be harder to treat.

LDH is an enzyme found in most body tissues. It is a marker of tissue turnover, which is a normal metabolic process. However, LDH levels should not be high.

Other blood serum markers to monitor melanoma treatment include S100 and melanoma-inhibitory activity (MIA).

The type of treatment a patient receives may determine the markers a doctor tests. For example, older research from 2017 suggests that MIA may be a useful marker to monitor the efficacy of immunotherapy in people with metastatic melanoma.

Learn more about LDH testing.

Complete blood count (CBC)

A CBC totals the number of blood cells a person has in a blood draw.

There are three types of cells included in a CBC:

• White blood cells (WBC): Also known as leukocytes, white blood cells are immune system cells that fight infection. They are in lymphatic tissue and blood.
• Red blood cells (RBC): Also called erythrocytes, red blood cells transport oxygen and carbon dioxide between the lungs and the rest of the body.
• Platelets: Also called thrombocytes, platelets enable the blood to clot.

CBC results can reveal the following:

• the state of a person’s general health
• the functioning of the spleen and bone marrow
• the presence of issues, such as:
  • anemia
  • infection
  • leukemia
  • blood disorders

For example, when monitoring melanoma, white blood cell counts can act as prognostic markers that help doctors estimate a person’s overall chance of survival. Ratios between different types of white blood cells can indicate a person’s level of immune response and act as biomarkers for treatment toxicity.

Blood chemistry tests

Doctors use a wide range of chemistry tests to assess different aspects of a person’s health.

They can test blood for:

• enzymes
• electrolytes
• lipids
• sugars
• proteins
• hormones
• vitamins
• minerals

Blood chemistry tests can provide doctors with information, such as a person’s metabolic and organ function.

For example, a normal creatinine test means a person’s kidneys function well enough to withstand a CT scan with contrast dye.

The following is a simplified version of the system the American Cancer Society uses to stage melanoma:

• Stage 0: The cancer exists only in the outermost layer of skin.
• Stage 1: The cancer is less than 2 millimeters (mm) thick with no signs of spreading.
• Stage 2: The cancer is 1–4 mm or larger with no signs of spreading.
• Stage 3: The cancer has spread locally but not to distant sites.
• Stage 4: The cancer has spread to distant sites, such as other organs.

Read about the survival rate by stage of melanoma.

Doctors diagnose melanoma using tools, such as biopsies and imaging.

Blood tests provide other information that can monitor a person’s health and influence treatment decisions.

Blood tests can also help doctors monitor cancer progression.