An Oncologist Explains "Routine" Blood Tests Performed in Cancer Patients.
by C.H. Weaver M.D. updated 5/2020
Simple blood tests are used to monitor the blood so doctors can determine the number of blood cells in circulation and the levels of chemicals, enzymes, proteins, and organic waste products that are normally found in the blood. The levels of blood cells, such as red blood cells, white blood cells and platelets, may be low in patients receiving treatment for cancer. Also, the levels of some chemicals normally found in the blood may be either too high or too low as a result of the cancer or its treatment. There are two types of blood tests typically performed during cancer treatment: the complete blood count (CBC) and a blood chemistry panel.
Doctors also perform more advanced tests using blood....
Complete Blood Count (CBC)
The CBC measures the levels of the three basic blood cells: red blood cells, white blood cells, and platelets. In the United States, the CBC is typically reported in the format shown in Table 1 below. It is important to understand not only which blood counts are being tested, but also how those results are reported. You will want to pay careful attention to the results column, which shows any results that are normal and the flag column, which shows any results that are abnormal.
Table 1: CBC with results and reference interval
Result column: The result column shows counts that fall within the normal range.
Flag column: The flag column shows counts that are lower (“L”) or higher (“H”) than the normal range.
Reference interval (or reference range) column: The reference interval shows the normal range for each measurement for the lab performing the test. Different labs may use different reference intervals.
White blood cells: White blood cells help protect individuals from infections. The above CBC report shows that the patient’s total white cell count is 1.5, which is lower than the normal range of 4.0-10.5. The low white cell count increases the risk of infection.
Absolute neutrophil count: Neutrophils are the main white blood cell for fighting or preventing bacterial or fungal infections. In the CBC report, neutrophils may be referred to as polymorphonuclear cells (polys or PMNs) or neutrophils. The absolute neutrophil count (ANC) is a measure of the total number of neutrophils present in the blood. When the ANC is less than 1,000, the risk of infection increases. The ANC can be calculated by multiplying the total WBC by the percent of polymorphonuclear cells. For example, this patient’s ANC is 0.34, which equals (WBC) 1.5 x 23%.
Red blood cells: Red blood cells carry oxygen from the lungs to the rest of the body. The above CBC report indicates that the patient has a red cell count of 3.5, which is lower than the normal range of 4.70-6.10, and therefore, shown in the flag column.
Hemoglobin (Hb or Hgb): Hemoglobin is a protein in the red cell that carries oxygen. The above CBC report indicates that the patient’s Hb count is 10.8, which is below the normal range of 14.0-18.0. The hematocrit (HCT), another way of measuring the amount of Hb, is also low. This means that the patient has mild anemia and may be starting to notice symptoms.
Platelets: Platelets are the cells that form blood clots that stop bleeding. The above CBC report indicates that the platelet count for this patient is normal.
Blood Chemistry Panel
The blood chemistry panel measures the levels of chemicals, enzymes, and organic waste products that are normally found in the blood. The results of a blood chemistry panel are typically reported with the name of the substance, the result, and the reference interval, as shown in Table 2. The reference interval is the normal range for that laboratory. Reference intervals may vary between laboratories. Substances that are typically measured in cancer patients are as follows:
Table 2: Sample blood chemistry panel with results and reference interval
Albumin is the most prevalent protein in the blood. It is synthesized in the liver and removed from circulation by the kidney, which causes it to be excreted in the urine. Albumin is often measured in order to detect liver damage or kidney damage, either of which may be a side effect of cancer or cancer treatment.
Alanine aminotransferase (ALT) is an enzyme in the liver that rearranges the building blocks of proteins. It is released from damaged liver cells. Cancer patients may experience liver damage as a side effect of some cancer treatments or due to spread of cancer to their liver. ALT may also be referred to as SGPT (serum glutamic pyruvic transferase.)
Aspartate aminotransferase (AST) is an enzyme in the liver that rearranges the building blocks of proteins. It is released from damaged liver cells. Cancer patients may experience liver damage as a side effect of some cancer treatments or due to spread of cancer to their liver. AST may also be referred to as SGOT (serum glutamic oxaloacetic transaminase.)
Alkaline phosphatase is an enzyme is that involved in bone growth. It is processed in the liver and excreted into the digestive tract in the bile. A higher than normal amount of alkaline phosphatase indicates bone or liver problems. In cancer patients, elevated alkaline phosphatase may indicate that cancer has spread to the bones or that liver damage, possibly due to some chemotherapy drugs, has caused problems with bile excretion.
Bilirubin is a substance that is formed from broken down red blood cells. It becomes part of bile, which is produced by the liver. A build-up of bilirubin can cause jaundice and may be measured to test for liver or bile duct function, which may be compromised if there is cancer in the liver or if there is liver damage. Some chemotherapy drugs may cause liver damage.
BUN (blood urea nitrogen) is a part of urea, the waste product that is left over from the breakdown of protein. Urea circulates in the blood until it is filtered out by the kidneys and excreted in the urine. If the kidneys are not functioning properly, there will be excess urea in the bloodstream, resulting in higher than normal BUN levels. Cancer patients may have elevated BUN if they have been treated with certain chemotherapy drugs that may cause kidney damage.
Calcium is a chemical that is necessary for muscle contraction, nerve function, blood clotting, cell division, healthy bones and teeth. An increased level of calcium in the bloodstream is a possible complication of cancer and is referred to as hypercalcemia. In its severe form, hypercalcemia may be a life-threatening emergency.
Chloride is a chemical that helps maintain fluid balance in the body. Low chloride levels may be caused by vomiting or diarrhea.
Creatinine is a compound that is produced by the body and excreted in the urine. Compounds that leave the body in the urine are processed by the kidney, therefore creatinine may be used to monitor for kidney function. Some cancer treatments may cause kidney damage.
Glucose is the simplest form of sugar that the body uses for energy. The body requires insulin to move sugar from the bloodstream into the cells for energy production. An abnormal glucose reading may signify a problem with insulin production, which occurs in the pancreas.
Lactate dehydrogenase (LDH) is involved in producing energy and is released from damaged cells in many areas of the body, including the heart and liver. Cancer patients may have an elevated LDH due to spread of cancer to their liver or damage to their liver from certain cancer treatments. For more information, go to Liver Damage. LDH is also considered a tumor marker, which is a substance that occurs at higher than normal amounts in the presence of cancer.
Magnesium is a chemical that is necessary for muscle contraction, nerve function, heart rhythm, bone strength, generating energy, and building protein.
Potassium is a chemical that regulates heart contraction and helps maintain fluid balance. Low sodium levels may be caused by vomiting or diarrhea.
Sodium is a chemical that helps maintain fluid balance and is necessary for muscle contraction and nerve function. Low sodium levels may be caused by vomiting or diarrhea.
Uric Acid is the end product of the digestion of certain proteins and is normally eliminated through the urine. Excess uric acid may be a side effect of some cancer treatments, and may lead to a condition called tumor lysis syndrome. When excess uric acid is present, it is converted to crystal. These crystals may be deposited in the tiny tubes that are part of the kidney and cause acute kidney damage, which can ultimately lead to kidney failure.
Additional results that are sometimes included in the blood chemistry panel are measures of the blood’s clotting capacity. Some cancer treatments reduce the number of platelets in circulation, which can cause the blood to clot more slowly so that the patient is more susceptible to excessive bleeding.
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Table 3: Measures of the blood’s clotting capacity
Activated Partial Thromboplastin Time (aPTT) is a measure of bleeding and clotting and is used to evaluate unexplained bleeding or monitor heparin treatment. Heparin is a drug that is administered to increase the clotting capacity of a patient’s blood. Some cancer patients may receive heparin as treatment for a low platelet count, or thrombocytopenia, which is a side effect of some cancer treatments. This condition can lead to more easy bruising and bleeding.
Prothrombin time (PT) is the most common way to express the clotting capacity of blood. PT results are reported as the number of seconds the blood takes to clot when mixed with a thromboplastin reagent. The International Normalized Ratio (INR) was created by the World Health Organization because PT results can vary depending on the thromboplastin reagent used. The INR is a conversion unit that takes into account the different sensitivities of thromboplastins. The INR is widely accepted as the standard unit for reporting PT results. Cancer patients may have an abnormally low PT/INR due to a lower than normal platelet count. Platelets are the components of blood that stop bleeding by clotting the blood. A low platelet count, also called thrombocytopenia, and a low PT may lead to more frequent bruising and bleeding.
More Specialized Blood Tests:
Ferritin is a protein that contains iron and is the primary form of iron stored inside of cells. The small amount of ferritin that is released and circulates in the blood is a reflection of the total amount of iron stored in the body. Ferritin can be measured in the blood and A ferritin test helps your doctor understand how much iron your body stores. If a ferritin test reveals that your blood ferritin level is lower than normal, it indicates your body's iron stores are low and you may have iron deficiency. High levels of ferritin can indicate an iron storage disorder, such as hemochromatosis, or a chronic disease process. Low levels of ferritin are indicative of iron deficiency, which causes anemia (a reduction in the number of oxygen-carrying red blood cells).