Questionable Lab Results

At times we receive laboratory results which just don’t seem to reflect what we expect. Some physicians are unconcerned when results are “within normal limits”. But “normal” doesn’t always apply to thyroid cancer patients when we no longer have a thyroid, leaving us to explore possible causes and solutions ourselves

These are some things to review when results seem off base:

  • Lab error – mislabeled or wrong tubes used
  • Different lab or change in lab procedures
  • Taking biotin (multi vitamins, hair/nail vitamins, B-complex, sports/energy drinks or bars)
    • Biotin should be held at least 72 hours, longer if high dose.
  • Different time of day
    • Many hormones have a circadian rhythm.
    • Consistency in checking labs is important: time of day, adequate time since last dose.
  • Recent illness.
    • Inflammation can lower Free T3, causing TSH to rise.
    • Severe illness
    • Flare of other autoimmune conditions
  • Recent vaccination.
    • Most cause some level of inflammation (part of how they work).
  • Recent prescription refill (within past few months even if same brand)
  • Other labs: Chemistry, CBC, Iron panel, vitamins D and B12.
    • Thyroid changes should be viewed in the context of the entire person.
    • Anemia, low vitamin D, selenium deficiency, etc. can affect conversion of T4 to T3.
    • Other conditions may affect absorption or drug metabolism
  • Changes in diet, activity level
    • May increase or decrease energy requirement or intake
  • Pregnancy, peri-menopause or HRT.
    • There is “cross talk” between thyroid hormone and sex hormone receptors.

Keeping a spreadsheet or chart showing historical levels over time, keyed to changes in medication and lifestyle, can help spot trends related to dose or other changes. It’s important that Free T3 (FT3) be tested and tracked, along with Free T4, TSH and Thyroglobulin (Tg). Any of the above factors can affect FT3 levels which, in turn, can affect TSH and Tg levels.

The first thing to do when lab results aren’t as expected based on history and clinical presentation is to repeat the lab work. A life altering care decision should never be made based on a single abnormal finding without confirmation and any sudden  or significant change needs to be investigated further.

It’s usually up to the patient to take a step by step approach to rule out possible triggers for a sudden change or to spot trends and determine the cause. A supportive PCP (or OB/Gyn for women) can be helpful in coordinating lab work, ruling out dietary deficiencies and suggesting other changes which may be affecting thyroid hormone metabolism or limiting T4 to T3 conversion.

If repeat lab work shows both low in range FT4 and FT3 with a higher TSH or Tg than expected this indicates an increase in the T4 (thyroxine) dose is likely needed. 
If it shows a mid to high FT4 level but low in range FT3, the simple addition of some synthetic T3 or change to desiccated thyroid may be helpful in lowering TSH and Tg.
The exact balance needed is very individual and may change over time. There are no “perfect” or “target” levels which will work for everyone. 

But if increased TSH and Tg persist despite the above factors being addressed and FT4/FT3 are at “optimal” or high levels (not necessarily simply “in range”) I would expect additional testing to either rule out pituitary dysfunction or explore the possibility of recurrence of thyroid cancer.

Additional Reading

Helpful Checklists and Trackers

What Blood Tests Should I Request?

Percent through Range

Quick Thyroid Tour

Rethinking Hypothyroidism