Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
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Discordant thyroid test panel chart

Mis-leading Test

Result

Likely Causes Action
TSH FT4

free T4

incr

N

  1. untreated - mostly biochemical sublinical & intermittent hypothyroidism is a borderline status wherein the body cycles in and out of the thyroid being able to keep up with life demands1.

  2. untreated-mild hypothyroidism which is worse than #1, thyroid-underserved episodes becoming longer & maybe a little clinically positive1.
  3. Treated - inadequate Synthroid dose or non-compliance
  1. Measure TPO Ab. Confirm TSH after 6 weeks of medication.
  2. Increase dose/counsel compliance.
decr  N or decr
  1. Mild (subclinical) hyperthyroidism
  2. Over treatment with T3-containing prep., factitial or not.
  1. ? Autonomous functioning goiter.
  2. Measure FT3 to rule out T3-toxicosis.
N incr
  1. Common during L-T4 treatment.
  2. Abnormally tenacious binding proteins (i.e. FDH*)
  3. Antibody interferences (T4 antibody, HAMA** or rheumatoid factor)
  1. Expect higher FT4 in L-T4 Rx. hypo.
  2. Check FT4 by alternate FT4 method ideally one using physical separation i.e. equilibrium dialysis or ultrafiltration
N decr
  1. Binding-protein competitor drugs
  2. Pregnancy
  1. Check FT4 by method using minimal dilution.
  2. Check FT4 by albumin insensitive method.  Use method and trimester-specific reference ranges.

TSH

incr

N

  1. Dysequilibrium (first 6-8 weeks of L-T4 Rx for 1 hypothyroidism)
  2. HAMA** & other interferences
  1. Recheck TSH before adjusting L-T4 dose.  High TSH persists for months after Rx. severe hypo.
  2. Check TSH (new specimen) by alternate method.
decr

N

  1. Dysequilibrium (first 2-3 months post Rx. for hyperthyroidism)
  2. Medications, i.e., glucocorticoids, dopamine
  3. surreptitious intake of thyroid replacement (SynthToid or even internet purchased t4 or T3 or mixed)...factitial thyrotoxicosis.
  4. borderline hypopituitarism in a relatively inactive patient
  1. Use FT4 and FT3 during early Rx. of hyper to monitor thyroid status.  TSH may take months to normalize after starting Rx. for severe hyperthyroidism.
  2. ask about meds
  3. ask carefully about use of Synthroid or other replacements or suppliments to boost energy and/or lose weight
  4. free T4 & free T3 might still show up in normal range

N or incr

incr
  1. TSH-secreting pituitary adenoma
  1. Check TSH (new specimen) by alternate method.
  2. TRH-stim or thyroid hormone suppression test.
  3. TSH alpha subunit.
  4. Pituitary imaging.

N

decr
  1. Central hypothyroidism
  1. Reduced bioactivity of immunoreactive TSH
  2. ? other signs of pituitary deficiency.
  3. ? blunted (< 2 fold) TRH response.

familial dysalbuminemic hyperthyroxinemia (FDH) Journal of Clinical Endocrinology & Metabolism, Vol 61, 783-786, Copyright © 1985

Common conditions that decrease the diagnostic accuracy of current free hormone tests in ambulatory patients include: 

  • severe congenital TBG abnormalities (TBG excess or deficiency); 
  • Familial Dysalbuminemic Hyperthyroxinemia (FDH); 
  • T4 and T3 autoantibodies and 
  • interfering substances such as Rheumatoid Factor and Heterophile antibodies (HAMA)

Excellent web source: Thyroid Disease Manager...click to area about strange test results.

thyroid tests Practice Guidelines, National Academy of Clinical Biochemistry (NACB), USA.

References:

  1. Fatourechi V, "Subclinical Hypothyroidism: An Update for Primary Care Physicians", Mayo Clinic Proceedings 84(1):65-70, January 2009.

  (posted 4 August 2003; latest addition 17 January 2009)

 
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