From the Guidelines
The primary blood test for medullary thyroid cancer is the calcitonin test, often accompanied by carcinoembryonic antigen (CEA) measurement. These tests are essential for diagnosis, monitoring treatment response, and detecting recurrence. Calcitonin is a hormone produced by C-cells in the thyroid, which are the cells that become cancerous in medullary thyroid cancer. Elevated calcitonin levels strongly suggest medullary thyroid cancer, with levels typically above 100 pg/mL being concerning. CEA is a complementary tumor marker that helps assess disease burden and progression.
According to the most recent and highest quality study 1, measurement of serum calcitonin is a reliable tool for the diagnosis of medullary thyroid cancer, with higher sensitivity compared to fine needle aspiration cytology (FNAC). The study also highlights the importance of incorporating calcitonin measurement into the diagnostic evaluation of thyroid nodules.
Some key points to consider when using the calcitonin test include:
- For screening high-risk individuals with genetic predisposition (MEN2 syndrome or RET gene mutations), calcitonin testing should begin in early childhood and continue regularly 1.
- After treatment, these blood tests are typically performed every 3-6 months for several years, then annually if stable.
- Sometimes doctors may order a calcium-stimulated calcitonin test, which can detect smaller amounts of disease by measuring calcitonin response after calcium administration.
- These blood tests are valuable because medullary thyroid cancer doesn't concentrate radioactive iodine like other thyroid cancers, making biochemical monitoring particularly important for management.
It's worth noting that other studies, such as 1 and 1, also support the use of calcitonin testing for medullary thyroid cancer diagnosis and management. However, the most recent and highest quality study 1 provides the strongest evidence for this recommendation.
From the Research
Blood Test for Medullary Thyroid Cancer
- The blood test for medullary thyroid cancer typically involves measuring the levels of calcitonin and carcinoembryonic antigen (CEA) in the blood 2, 3, 4, 5, 6.
- Calcitonin is a sensitive tumor marker for the detection of medullary thyroid carcinoma (MTC), and its levels can be used to assess tumor burden and progression status 2, 5, 6.
- The doubling times of calcitonin and CEA are also useful in assessing tumor progression, with shorter doubling times indicating more aggressive disease 2, 5.
- However, there are cases where serum calcitonin levels are not elevated, despite the presence of MTC, making diagnosis and surveillance challenging 3, 4.
- In such cases, other biomarkers like procalcitonin, chromogranin A, and carcinoembryonic antigen may be useful in diagnosis and follow-up 4.
- The European Thyroid Association's guideline advocates calcitonin determination in people with thyroid nodules, but the role of routine calcitonin testing is still questionable due to the low prevalence of MTC 6.
- Studies have shown that basal and stimulated calcitonin testing have high sensitivity and specificity for detecting MTC, but the positive predictive value is low due to the low prevalence of the disease 6.
Diagnostic Accuracy of Calcitonin Testing
- The sensitivity of basal calcitonin testing ranges from 83% to 100%, and specificity ranges from 94% to 100% 6.
- The estimated sensitivity and specificity of basal calcitonin testing at a threshold of 10 pg/mL are 100% and 97.2%, respectively 6.
- Combined basal and stimulated calcitonin testing also has high sensitivity and specificity, ranging from 82% to 100% and 99% to 100%, respectively 6.
Limitations and Future Directions
- The current evidence is limited by the absence of adequate reference standards and follow-up in calcitonin-negative participants, resulting in a high risk of bias 6.
- Further studies are needed to define options for management of non-secretory MTC and to identify new and reliable biomarkers associated with diagnosis and relapse of this disease 4.