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Pitfalls in the interpretation of thyroid function tests - how to avoid being caught out…
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Mark Gurnell
BG
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University of Cambridge
Wellcome Trust-MRC Institute of Metabolic Science
ADDENBROOKE’S HOSPITAL Cambridge University Hospitals NHS Foundation Trust
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Potential pitfalls in TFT interpretation When to tread carefully…
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1. TFTs discordant with the clinical picture
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2. TFTs discordant with each other
‘Anomalous TFTs’ ‘Discordant TFTs’ ‘Funny TFTs’ ‘Perplexing TFTs’ ‘Puzzling TFTs’ ‘Weird TFTs’
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Required knowledge for resolving discordant TFTs 1. Physiology of the HPT axis and factors that govern thyroid hormone action at a tissue and cellular level
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2. Principles underpinning laboratory measurement of T4, T3 and TSH; potential mechanisms of assay interference
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3. Conditions associated with ‘discordant TFTs’ ‘Anomalous TFTs’ ‘Discordant TFTs’ ‘Funny TFTs’ ‘Perplexing TFTs’ ‘Puzzling TFTs’ ‘Weird TFTs’
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Thyroid hormone action and regulation
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TRH SA
-
+ - T3←T4
BG
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TSH
TBG/ Albumin/ Prealbumin
-
T3 T4
T3←T4
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Thyroid hormone action and regulation TRH SA
T3 MCT8
CoA T3
RXR TR
DNA
-
+ - T3←T4
TSH
+++
S
TRE
+ve
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T4
BG
T4
T3
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Deiodinase
TBG/ Albumin/ Prealbumin
-
T3 T4
T3←T4
Koulouri et al, 2013. Best Pract & Res Clin Endo Metab, 27: 745-62. Koulouri & Gurnell, 2013. Clin Med, 13: 282-86. Gurnell et al 2011. Clin Endocrinol, 74: 673-78.
• subclinical hyperthyroidism • recent Rx for hyperthyroidism • drugs (e.g. steroids, dopamine) • assay interference • NTI
• NTI • central hypothyroidism • isolated TSH deficiency • assay interference
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TFT pattern recognition
Thyrotoxic FT4/FT3
↔ TSH ↓*
TSH ↓
↓ TSH ↔ or ↓* FT4/FT3
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FT4/FT3
↑
‘Normal’
↔ TSH ↔ FT4/FT3 ↓ TSH ↑
FT4/FT3
↔ TSH ↑
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FT4/FT3
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• subclinical hypothyroidism • poor compliance with thyroxine • malabsorption of thyroxine • drugs (e.g. amiodarone) • assay interference • NTI recovery phase • TSH resistance
↑ TSH ↔ or ↑ FT4/FT3
• assay interference; FDH • thyroxine replacement therapy Hypothyroid (including poor compliance) • drugs (e.g. amiodarone, heparin) • NTI (incl acute disorders); neonatal period • TSH-secreting pituitary adenoma • Resistance to thyroid hormone (RTH) • Disorders of thyroid hormone transport or metabolism
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Illustrative cases
47-yr-old woman Increasing tiredness and fatigue
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PC
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Case 1 – clinical vignette
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HPC 6 month history of: - general deterioration - marked tiredness and fatigue - excessive sleepiness Stable weight, no constipation
DH
BG
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PMH Radioactive iodine therapy for hyperthyroidism (1991) Thyroxine 275 mcg/day Morphine sulphate, gabapentin, citalopram, diazepam
kg/m2
BMI 33.1 (Wt 88 kg) normal secondary sexual features no palpable thyroid gland myxoedematous facies slow-relaxing reflexes
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O/E -
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Case 1 – examination & initial investigations
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- ankle oedema - bibasal lung crepitations
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- visual fields full to confrontation
TSH
(0.4–4.0)
FT4
(9.0–20.0)
FT3 (3.0–7.5)
TPO TRAb
>100 mU/L 0.3 pmol/L 1.9 pmol/L negative negative
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Case 1 – question Which is the most likely explanation for this lady’s failure to respond to supraphysiologic thyroxine therapy? Elevated T4 & T3 binding capacity
B
Enhanced metabolism of thyroxine
C
Increased deiodination of T4 to rT3 (reverse T3)
D
Malabsorption
E
Non-concordance with thyroxine therapy
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A
kg/m2
BMI 33.1 (Wt 88 kg) normal secondary sexual features no palpable thyroid gland myxoedematous facies slow-relaxing reflexes
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O/E -
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Case 1 – examination & initial investigations
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- ankle oedema - bibasal lung crepitations
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- visual fields full to confrontation Clinical D: Poor (non!) concordance
TSH
(0.4–4.0)
FT4
(9.0–20.0)
FT3 (3.0–7.5)
TPO TRAb
>100 mU/L 0.3 pmol/L 1.9 pmol/L negative negative
Coeliac serology
negative
Faecal elastase
normal
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Case 1 – review of historical TFTs TSH
Free T4
Thyroxine
(0.5–4.2 mU/L)
(9.7–25.7 pmol/L)
(mcg/day)
05/06
100
1.7
250
06/10
>100
1.9
300
BG
07/09
S
06/09
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‘Lost to follow up’
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Anomalous TFTs in patients receiving L-T4 therapy Consider Assay Interference
Drugs
Dietary factors Fibre Espresso Coffee
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Consider TH malabsorption GI Disorders
Binding capacity
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Oral E2 therapy SERMs Mitotane
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Coeliac disease Lactose intolerance Achlorhydria
Consider increased metabolism/excretion/ binding capacity
Investigations
Prescription history L-T4 absorption test Supervised dosing
Consider Compliance
Cholestyramine FeSO4 Sucralfate Aluminium hydroxide Calcium carbonate Sevelamer HCl PPIs Orlistat
Metabolism Carbamazepine Phenytoin Phenobarbitone Rifampicin Imatanib
Weekly Dosing may be a treatment option
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Case 1 – supervised thyroxine administration
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CASE A: L-T4 800g p.o. tablets
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12 10 8 6
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4 2 0
100
BG
0
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Free T4 (pmol/L)
14
200
300
CASE 1: L-T4 800g p.o. liquid
CASE 1: L-T4 800g p.o. tablets
400
Time (mins)
Do not underestimate the ingenuity of your patients!
SUPERVISED THYROXINE ABSORPTION TEST
Koulouri et al, 2013. Best Pract Res Clin Endo Metab 27:745-762
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Pre-test: • Exclude: confounding dietary factors/medications conditions associated with thyroxine malabsorption (e.g. coeliac disease, achlorhydria, lactose intolerance) overt non-compliance (e.g. failure to collect regular thyroxine prescription) assay interference • Check no contraindications to high-dose thyroxine therapy (consider performing ECG)
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On day of the test: • Ensure patient: has fasted from midnight empties bladder immediately prior to dosing (to allow continuous observation for 60 min post-dosing) • Under direct supervision, administer the equivalent of one week’s cumulative thyroxine dose [e.g. 1.6 body weight (kg) 7 mcg] in liquid (preferred option) or tablet form (with dose rounded to nearest 50 mcg) • Follow immediately with 200mL water orally, and observe patient for 60 min (keep fasted during this time) • Collect blood samples for measurement of FT4, FT3 and TSH at 0, 30, 45, 60, 90, 120, 240 and 360 min
SUPERVISED THYROXINE ABSORPTION TEST
Koulouri et al, 2013. Best Pract Res Clin Endo Metab 27:745-762
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Post-test: • Continue weekly supervised (observed for 60 min) administration of the same dose of thyroxine for a further 5 weeks • Collect blood samples for measurement of FT4, FT3 and TSH at 0 and 120 min at weeks 2, 3, 4, 5 and 6
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Interpretation and follow-up: •TSH normalization non-compliance; explore patient perspective; consider continued weekly dosing •Inadequate FT4 rise post-thyroxine administration institute further investigations for malabsorption •Consistent rises in FT4 post-thyroxine, but no change in TSH levels consider dose adjustment and/or further investigations into disorders of TH metabolism/excretion
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Case 2 – a near miss…! Pituitary MRI:
+ 5 months
+ 5 years
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Presentation
D: Correction of poor-compliance with L-T4 therapy → reversible thyrotroph hyperplasia
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Case 3 – clinical vignette & investigations 77-yr-old female
Fall → left fractured neck of femur
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PC
TSH
PMH Hypertension (amlodipine 10mg/day)
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Euthyroid; no goitre AF 110 bpm; no cardiac failure Nil else of note
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O/E
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Post-operatively: developed AF
(0.4–4.0)
FT4
(9.0–20.0)
TPO TSH (0.4–4.0)
TT4 (53–135)
3.2 35.0 negative
3.1 118
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Case 3 – question Which is the most likely explanation for this pattern of TFTs?
Drug effect
B
Non-thyroidal illness (sick euthyroid syndrome)
C
Radiographic contrast agent-induced thyrotoxicosis
D
Subclinical hyperthyroidism
E
TSH-secreting pituitary adenoma (TSHoma)
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A
Heparin
LPL
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Tg
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Heparin-induced elevation in free thyroid hormone levels
T4
Tg FFA Tg
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T4
T4
T4
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T4
Stevenson et al, 2002. Clin. Chem. 44; 1002-7.
Heparin
LPL
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Tg
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Heparin-induced elevation in free thyroid hormone levels
T4
Tg FFA Tg
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T4
T4
T4
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T4
Stevenson et al, 2002. Clin. Chem. 44; 1002-7.
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Non-thyroidal illness (NTI; ‘sick euthyroid syndrome’) Definition:
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Any condition, not directly affecting the HPT axis, that is accompanied by abnormal thyroid function tests Patterns of thyroid function tests in NTI:
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• Thyroxine: total T4 (TT4) free T4 (FT4)
– depressed or normal
– normal / reduced / (elevated) – normal / reduced / (elevated)
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• Thyrotropin (TSH)
• Triiodothyronine (T3) total T3 (TT3) free T3 (FT3)
– reduced / (normal) – reduced / (normal)
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Non-thyroidal illness (NTI; ‘sick euthyroid syndrome’) Aetiology/Pathogenesis:
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Contentious but may include: • alterations in serum thyroid hormone binding capacity • reduced cellular uptake of T4 • decreased peripheral conversion of T4 to T3 • reduced hypothalamic (TRH) pituitary (TSH) secretion (role of IL-1, IL-6, leptin, glucose and O2 availability) Other factors: • cortisol / exogenous glucocorticoids / dopamine
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Adaptive vs Maladaptive?
• Induced hypothyroidism – a ‘beneficial’ response or • Central hypothyroidism – a potentially ‘disadvantageous’ response?
Koulouri et al, 2013. Best Pract Res Clin Endo Metab 27:745-762.
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Algorithm for discordant TFTs Step 1: re-evaluate clinical history Pregnancy changes Consider: ↓ TSH (first trimester; secondary to ↑ hCG) ↑ TT4 and ↑ TT3 (from first trimester; secondary to ↑ TBG) Changes in FT4 and FT3 Pregnancy RR
Consider: Confounding dietary factors or medications Malabsorption syndromes Altered TH metabolism Non-compliance Other factors
Confounding medications
Non-thyroidal illness
Consider: Amiodarone Furosemide Heparin Corticosteroids Dopamine Others
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Consider: Neonatal period Elderly
Thyroxine therapy
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Age
hCG, human chorionic gonadotropin; RR, reference range; TBG, thyroxine-binding globulin; TFT, thyroid function test; TH, thyroid hormone; TT3, total triiodothyronine; TT4, total thyroxine
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Case 4 – clinical vignette 78-yr-old male
O/E
Tiredness
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HPC 6 month history of: • tiredness • cold intolerance • dry skin
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PC
Bicalutamide
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DH
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PMH Prostate carcinoma
Clinical impression: Hypothyroidism
P=60 bpm SR No goitre
(11.0–22.0)
TSH (0.35–5.5)
TPO
16.3 mU/L
2551 U/L
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(0–100)
51.0 pmol/L
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FT4
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Case 4 – initial investigations
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Case 4 – question Which is the most likely underlying diagnosis?
Factitious hyperthyroidism (covert thyroxine administration)
B
Hashitoxicosis (thyrotoxic phase of Hashimoto’s disease)
C
Primary autoimmune hypothyroidism
D
Resistance to thyroid hormone (THRB)
E
TSH-secreting pituitary adenoma (TSHoma)
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A
(11.0–22.0)
TSH (0.35–5.5)
TPO
16.3 mU/L
2551 U/L
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(0–100)
51.0 pmol/L
TRH test
Time
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FT4
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Case 4 – further investigations
TSH (mU/L)
0 20’
16.3 32.0
60’
58.0
FT3 (3.0–7.5)
2.9 pmol/L
FT4
2.0
5.0
(pmol/L)
(7.5–21.1)
(8.0–21.0)
TSH
25.0
22.0
(mU/L)
(0.3-5.6)
PerkinElmer (Wallac) DELFIA
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(0.2-4.5)
Roche E170
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Abbott AxSYM
Immulite 2500
Bayer Centaur
3.3
19.5
21.6
44.7
(9.0–20.0)
(12.0–22.0)
(10.0–24.0)
(11.0–22.0)
25.0
30.0
(0.4–4.0)
(0.3-4.5)
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Beckman Access
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Case 4 – further investigations
24.5 (0.35–5.5)
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FT4/FT3: ‘1-step’ competition assays
T3/T4
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T3/T4
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Enhancement Solution
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= endogenous T3/T4 = competing labelled T3/T4
variant albumin T3/T4 binding Ab
Fluorescence Measurement
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FT4/FT3: ‘2-step’ assays Wash
Enhancement Solution
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T3/T4
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Wash
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T3/T4
Fluorescence Measurement
(7.5–21.1)
(8.0–21.0)
25.0
22.0
(0.3-5.6)
(0.2-4.5)
Roche E170
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(mU/L)
5.0
PerkinElmer DELFIA
TWO STEP FT4 assays
Immulite 2500
Bayer Centaur
3.3
19.5
21.6
44.7
(9.0–20.0)
(12.0–22.0)
(10.0–24.0)
(11.0–22.0)
25.0
30.0
(0.4–4.0)
(0.3-4.5)
Au
TSH
2.0
S
(pmol/L)
Abbott AxSYM
BG
FT4
Beckman Access
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Case 4 – further investigations
24.5 (0.35–5.5)
ONE STEP FT4 assays
Choose your ‘friends’ carefully (laboratory!)
Equilibrium Dialysis
Radiolabelled T4 binding
Dialysate
T3/T4 binding antibodies
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Free T4/T3
Equilibrium dialysis
FT4
0.4
(ng/dL)
(0.8-2.7)
BG
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binding proteins
Control serum: Patient serum:
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Serum
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Case 4 – further investigations