What Blood Tests Should I Request?

As thyroid cancer patients, when things are not going well the first place we tend to look is to our thyroid hormone replacement (THR) meds. Just as our thyroid interacted with every aspect of our physical and mental health, metabolism and daily activity, we need to remain aware of how our overall health works withn our meds but may find it challenging to figure out how to do this. We need to know what blood tests we shouold ask our doctors to order and which doctor is responsible for what.

Who should order my blood test?

Usually, at least in the beginning, an endocrinologist will order labs to check thyroid levels and cancer markers. Everything else that isn’t directly related to our thyroid cancer falls under the socpe of primary care. These relationships may vary from doctor to doctor and also change and evolve over time.

Cancer survivorship care at some point can transition from the intensity of the oncologist or other cancer specialist to the primary care provider for long term management. The PCP can easily take over basic monitoring of thyroid levels and make this part of the thyroid patient’s overall health planning. The PCP is in a postion to look at the whole picture rather than seeing us as isolated body systems.

Some test results are actionable by themselves, such as a low vitamin D3 result which would suggest supplementing with vitamin D. 

Most test results should be viewed in context with other tests, history and symptoms. For example, a low red blood cell count (RBC) might trigger looking at B12 and folate levels, iron tests and kidney function, or a high calcium level might warrant checking a PTH level.

General Health Basics

Blood tests usually start with the “basic” CBC and CMP most of us are familiar with. Someone in perfect health with no complaints may agree with their doctor that additional basic tests really aren’t needed. A patient having difficulty optimizing their thyroid levels or having symptoms would want to look at more in depth testing.

  • CBC – Complete Blood Count. Looks at red and white blood cells which can indicate anemia, infection/inflammation
  • CMP – Comprehensive Metabolic Panel plus magnesium and phosphorus. Looks at liver and kidney function, electrolytes and protein. Magnesium and phosphorus are not normally included in a CMP but are important in bone and cardiac metabolism.
  • Vitamin D3 – essential to maintenance of bone health
  • Vitamin B12 and Folate – play an important role in forming red blood cells
  • Iron Panel – 
    • Ferritin – reflects iron stores
    • Iron  – circulating levels of iron
    • Transferrin – protein that transports iron 
    • TIBC – indirectly reflects available transferrin
    • UIBC – unsaturated iron-binding capacity, transferring reserve

Thyroid Levels

These are the essential thyroid level tests which support our interpretation of how we are responding to our THR therapy. It’s possible to maintain TSH suppression to lower risk of recurrence with symptom-free THR dosing – this requires more than just looking at TSH. Additionally while thyroid hormone dosing is done in very small increments, — micrograms — the laboratory reference ranges for TSH, Free T4 and Free T3 are quite broad.

While we definitely want to ward off a return of our thyroid cancer we also have a life to live; we want our doctor to “Treat the patient, not the numbers.”

  • TSH – measures hypothalamus–pituitary response to circulating thyroid hormones
  • Free T4 – measures unbound circulating thyroxine (T4)
  • Free T3 – measures unbound circulating triiodothyronine (T3), the biologically active hormone
  • Reverse T3 – measures the amount of T4 converted to an inactive isomer of T3* (While reverse triiodothyronine has no demonstrated biological activity it can help clarify the cause of poor response.)

Thyroid Cancer Markers

These are the primary markers which are assessed periodically to monitor for recurrence. The frequency depends on the patient’s risk factors.

  • Thyroglobulin (Tg) and Tg Antibodies (TgAb) – see Tg Testing with Antibodies
  • Calcitonin – cancer marker for medullary thyroid cancer
  • CEA – used together with calcitonin.

Additional In Depth Testing

These are additional tests which some thyroid cancer survivors have found helpful.

  • Homocysteine – concentration may be elevated before B12 and folate tests are abnormal. 
  • RBC Folate – red blood cell folate measurement more closely reflects tissue stores
  • MMA – methylmalonic acid helps detect early or mild vitamin B12 deficiency.
  • PTH – parathyroid hormone, if calcium high or low or DEXA scan positive for bone changes 
  • Cortisol – morning blood level and/or diurnal saliva testing.
  • MTHFR Mutation – to evaluate the cause of elevated homocysteine levels (Methylenetetrahydrofolate Reductase Mutations, C677T and A1298C)

Further information and in depth test detail

https://labtestsonline.org/tests-index
https://www.labcorp.com/test-menu/search
https://www.lucatraining.org
https://www.nps.org.au/australian-prescriber/articles/treat-the-numbers-or-treat-the-patient