How does having cancer change patients’ routine laboratory test results?
A: Cancer develops and grows through a complex process involving genetic mutations, tumorigenesis, tumor biology, and pathobiology. This process not only causes disease-specific biological and pathological changes in cancer patients, but also triggers general biochemical changes either in systemic response to the cancer itself or to anti-cancer therapy. These changes are usually reflected in abnormal routine laboratory test results.
What routine lab tests are used to manage cancer?
These tests include clinical chemistry tests, immunoassays, and hematological tests, many of which provide information about a patient’s general health condition. Certain routine lab tests also indicate the pathological status of a patient’s malignancy. For example, calcium and lactate dehydrogenase (LDH) aid in cancer diagnosis and also help to monitor the course of disease in conjunction with other tests such as sodium, potassium, magnesium, phosphorus, glucose, iron, C-reactive protein (CRP), and uric acid. Results from these routine tests help guide treatment decisions for cancer patients as well. A number of studies have even shown that routine tests such as albumin, bilirubin, CRP, and LDH predict clinical outcome and overall patient survival.
Which routine lab tests are most likely to be altered by cancer?
The numerous biochemical test results that cancer affects include, but are not limited to: albumin, protein, electrolytes (sodium, potassium), calcium, magnesium, phosphorus, liver function tests (aspartate aminotransferase, alanine transaminase, alkaline phosphatase, gamma-glutamyl transpeptidase, bilirubin), renal function tests (blood urea nitrogen, creatinine), glucose, iron, lipids (total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol), CRP, uric acid, vitamin D, and LDH. The abnormal results from these tests can be either factual or factitious. In other words, they might be real high or low results, but they also sometimes represent false elevations or decreases.
What are examples of cases that result in routine biochemical abnormalities?
The abnormal blood test results caused by hematologic malignancies are among the most striking occurrences of this phenomenon. In multiple myeloma patients, elevated levels of monoclonal immunoglobulin lead to both false and real high calcium and phosphorus results, as well as false low readings for albumin, lipids, sodium, phosphorus, chloride, glucose, urea, creatinine, uric acid, and thyroxine. In leukemia patients, increased blood cell counts cause falsely high serum potassium (pseudohyperkalemia) and real high phosphorus due to hemolysis and the release of electrolytes from the excess blood cells. Furthermore, increased blood cell counts cause pseudohypoglycemia due to increased consumption and metabolism of glucose by leukocytes.
Beyond hematologic malignancies, increased calcium levels occur in cases of excessive parathyroid hormone secretion due to parathyroid adenoma, multiple endocrine neoplasia type 1, multiple endocrine neoplasia type 2A, carcinomas, and cancer with bone metastases. Chemotherapy and monoclonal antibody therapy also cause abnormal results for electrolytes such as sodium, magnesium, and phosphorus as well as other assays.
How should labs interpret routine test results in cancer patients?
Labs may find it helpful to develop investigation algorithms for abnormal results. When designing these algorithms, labs should keep in mind that factual changes to routine laboratory results largely reflect the pathobiology and biochemistry of cancer or the body’s response to therapy. Factitious lab results, on the other hand, tend to be caused by preanalytical and analytical factors associated with medical conditions in cancer patients. One example of this is pseudohyperkalemia in leukemia patients with increased blood cell counts, as mentioned earlier.
Above all, abnormal results need to be interpreted with caution and a thorough understanding of cancer biology, since misinterpretation could lead to inappropriate medical intervention and negative consequences for patients.
Qing H. Meng, MD, PhD, DABCC, is a professor and director of the clinical chemistry laboratories in the department of laboratory medicine at The University of Texas MD Anderson Cancer Center in Houston. +Email: [email protected]