Transcript Interpreting Thyroid Function Tests

Interpretation of laboratory thyroid
function tests
5 % of world
population suffers
from thyroid diseases
Hypothalamic-Pituitary-Thyroid Axis
Thyroid Hormones Affects
Many Organs and General Health
Eyes
Lungs
Brain
Heart
Skin
GI Tract
Liver
Kidney
Uterus
Thyroid Disease – Who Is At Risk ?
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All newborns (neonatal screening)
personal history of thyroid disease
strong family history of thyroid disease
Have an autoimmune disease, such as Type 1 Diabetes
Some genetic conditions (e.g. Down, Turner syndromes)
past history of neck irradiation
drug therapies such as lithium and amiodarone
women over age 35
elderly patients
Pregnant women during the first trimester
women 6 weeks to 6 months post-partum
Have elevated lipid levels
To screen or not to screen for thyroid
dysfunction
• American Association of Clinical
Endocrinologist (AACE), American Academy
of Family Physicians (AAFP), The American
College of Physician (ACP) and the
American Thyroid Association (ATA) vary
greatly in their recommendations.
• ATA recommending routine screening at age
35 then every five years
When the Thyroid Doesn’t Work
• Hyperthyroidism
• Hypothyroidism
Hypothyroidism
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More common than hyperthyroidism
99% is primary (< 1% due to TSH deficiency)
Hashimoto’s:
Most common cause of hypothyroidism
Goiter
Anti TPO antibodies (90%)
• Anti Thyroglobulin antibodies (20-50%)
 Postpartum (silent):
• Silent/painless
• Occurs within 6 weeks6 months postpartum
 Subacute thyroiditis:
• Most common cause of painful thyroiditis
2001; Intenzo CM, et al. Scintigraphic features of autoimmune thyroiditis. 21: 957-964
Common Signs and Symptoms
of Hypothyroidism
Dry skin
Brittle and lustreless hair
Weight gain
Tiredness
Constipation
Muscle aches
Bradycardia
Cold intolerance
Depression
Memory Loss
Heavy periods
Laboratory findings in Hypothyroidism
• Elevated TSH
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Low FT4
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TPO Ab (+)
• Macrocytic anemia due to VIT B12 deficiency
• ↑ CPK-MB
• ↑ LDL,↑ Chol (↓ lipid clearance)
•Hyponatremia
Hypothyroid Algorithm
TSH
Mildly Elevated
4 - 10 mIU/ml
W ithin Normal Limits
Type Title Here
Order FT4
Suppressed
Hypothyroid
Elevated
> 10 mIU/ml
FT4
Suppressed
W ithin Normal Limits
Thyroid Antibodies
Anti-TPO
Elevated
Autoimmune
Disease
Hypothyroid
Hyperthyroidism
• less common than hypothyroidism
• 99% is primary (< 1% due to TSH deficiency)
• Graves’ Disease
• Goiter
• Most common cause of hyperthyroidism
• Anti-TSH antibodies (80%)
• Toxic Nodular Disease
• Single or multiple nodules
• Occurs mostly in older age than graves
• T3 Thyrotoxicosis:
Approximately 5% of clinically hyperthyroid
patients with normal FT4
Common Signs and Symptoms
of Hypothyroidism
Worm moist skin
Hair loss
Weight loss
Nervousness
Increased bowel movements
Muscle weakness
Tachycardia
Heat intolerance
Insomnia
Difficulty in concentrating
Light or Absent periods
Laboratory findings in Hyperthyroidism
• TSH nearly undetectable
• Elevated FT4 or FT3
• Mild leukopenia
• N/N anemia
• ESR elevated
• ↑ LFT’s and alk phosph
• Mild ↑ Ca++
• ↓ Albumin
• ↓ Cholesterol
Hyperthyroid Algorithm
Sensitive TSH
0.1- 0-3 mIU/L
Borderline
Low TSH
0.3- 4.8 mIU/L
Within normal Limits
no further testing
indicated
< 0.1 mIU/L
Low TSH
Order FT4
FT4
If normal FT4
Hyperthyroid
Order FT3
Spectrum of Thyroid Disease
Sever
mild
Subclinical
Subclinical Thyroid Disease
• Asymptomatic
• Among the group with subclinical thyroid
disease, 73.8% are hypothyroid and 26.2% are
hyperthyroid.
• TSH outside the reference interval but normal
serum levels of T3 and T4
• The prevalence of SCH is about 4% to 10% in the
general population and may be as high as 20
percent in women older than 60 years
• Antithyroid antibodies can be detected in 80% of
patients with SCH.
• 80% of patients with SCH have a serum TSH of
less than 10 mIU/L.
• To treat or not to treat
Case Study
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A 30-year-old woman presents to gastroenterology clinic with
constipation in last 3 months
Also she developed fatigue and a weight gain of 9.1 kg in the past
6 months in spite of her tight trials for diet control.
She say she become to much depressed , asked psychiatric
advices and started antidepressant therapy which claimed as a
cause for her weight gain. She was planning for pregnancy
before.
She has a sister who is receiving levothyroxine therapy for
hypothyroidism.
On examination, she looked slightly pale, pulse 72/min regular,bl
pr 110/80,chest ,heart and abdomen :clinically free, thyroid is not
palpable.
All Laboratory tests are unremarkable except a serum TSH level
of 7 mIU/L. Thyroperoxidase (TPO) antibodies are detected.
Subclinical hypothyroidism
• The TSH level may be borderline elevated in the
presence of normal levels of fT4.
• Treatment for subclinical hypothyroidism is
recommended when:
 TSH greater than 10mU/L;
 TSH is above the upper reference interval limit,
but ≤10 mU/L and any of the following are
present:
• elevated thyroid peroxidase (TPO) antibodies
• goitre
• strong family history of autoimmune disease
• Pregnancy
• Dyslipidemia
Subclinical hyperthyroidism
 TSH level may be borderline suppressed in the
presence of normal levels of fT4
 Subclinical hyperthyroidism is much less
common than Subclinical hypothyroidism
 Treatment for subclinical hyperthyroidism is
recommended when:
• Any cardiac disease
• Age > 60
• Osteoporosis
Case Study
• 67 year old man admitted to the hospital
with severe decompensated CHF.
Responds to initial therapy in terms of
oxygenation, but does not regain normal
mental status as quickly.
• Lab work was done to rule out reversible
causes of altered mental status. TSH is
elevated at 13. On further testing, free T4
is normal, but T3 is low.
• Is this patient hypothyroid?
Sick Euthyroid Syndrome
• Thyroid related changes that occur during
systemic illness in the absence of intrinsic
thyroid disease
• The syndrome is acute, reversible, and occurs
commonly after surgery, starvation and in
many acute febrile illnesses, These changes
may be observed in up to 75% of hospitalized
patients
• Any abnormality in hormone level is possible,
usually low fT3
Drugs that can lead to alterations in
thyroid function
• Lithium: decreased TH release
• Amiodarone: iodine-rich drug widely used for the
management of arrhythmiaswhich may cause hypo or
hyperthyrodism
• Estrogens: Increase TBG, decrease FT4 level
• Androgens/corticosteroids : Decrease TBG, increase FT4
level
Misleading TSH Results
• TSH in normally released in a pulsatile fashion, peaking
during the night it generally takes 4-6 weeks for TSH levels
to reflect the status of thyroid hormone in the blood
• Acutely ill patients: “sick euthyroid syndrome”
• Following thyroid hormone replacement: “pituitary reset”,
wait 6-8 weeks before measuring TSH
• During treatment phase of hyperthyroid patients: “pituitary
reset”, wait 3 months before measuring TSH
• Patients with severe hypo- or hyperthyroidism may display
an abnormal TSH for several months after clinical
euthyroidism is achieved.
TSH Reference range ?
What the American Association of Clinical Endocrinologists
Said...
Thyroid Disease in Pregnancy
Three factors alter thyroid function in pregnancy
1) Transient ↑ in hCG, during the 1st trimester can
stimulate the TSH-R
- Gestational Transient Thyrotoxicosis (GTT)
- Hyperemesis gravidarum
2) E2-induced ↑ in TBG during the 1st trimester,
which is sustained during pregnancy affecting
TT4 and TT3
3) Alterations in immune function leading to onset,
exacerbation, or improvement of an underlying
autoimmune thyroid disease.
Thyroid Disease in Pregnancy
• Pre-pregnancy and early pregnancy:
 TSH screening for hypothyroidism is indicated in women
who are planning pregnancy or are in early pregnancy if
they have a goiter or strong family history of thyroid
disease.
• Pregnancy:
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TSH may be suppressed as a normal finding within the
first trimester of pregnancy. A normal fT4 generally
excludes hyperthyroidism.
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US Endocrine Society recommends thyroid function
screening for all pregnant women
• Post pregnancy:
 Post-partum thyroiditis (PPT) may occur in 5-10% of
women
Subclinical hypothyroidism with pregnancy
• Undetected SCH during pregnancy may
adversely affect the neuropsychological
development ,survival of the fetus
• Associated with hypertension and
toxaemia
• Subclinical hypothyroidism is associated
with ovulatory dysfunction and infertility..
Congenital Hypothyroidism
Because newborns are
asymptomatic at birth,
screening programs
developed worldwide
Incidence 1 in 3,000
One of the commonest
treatable causes of mental
retardation
Treating Thyroid Disorders
Hypothyroidism
Indications for LT4 replacement
 Asymptomatic: TSH > 10
 Asymptomatic and TPO Ab (+): TSH > 5
 Symptomatic: TSH > 5
 Pregnant female: TSH > 5
 Goitrous: TSH > 5
• Annual Monitoring only with TSH every 6 to 8 weeks
until the TSH level reaches 0.5mIU/L to 2.0 mIU/L
• After the TSH level has normalized, maintenance
dosage is continued and the TSH test repeated
annually or whenever the patient becomes
symptomatic
Treating Thyroid Disorders
Hyperthyroidism
• Radioiodine Therapy
• Stop Thyroid Hormone Production
• Anti-thyroid Drugs Often Helpful
• Surgery Maybe Necessary
• Once treatment begins, FT4 is recommended to
monitor therapy during early transition phase (
usually not more than 3 months )
• TSH is not recommended for following treatment of
hyperthyroidism unless FT4 drops to low-normal
levels, the thyroid gland enlarges and symptoms of
hypothyroidism present
Possible explanations for various result
combinations
High
TSH
Normal
TSH
Low
TSH
High T4
Normal T4
Low T4
Irregular use of thyroxine
Amiodarone
Pituitary hyperthyroidism
(TSH-producing pituitary
tumour - rare)
Thyroid hormone resistance
(very rare)
Subclinical hypothyroidism
T4 under replacement
Primary hypothyroidism
As above
Some drugs (steroids, betablockers, NSAIDS)
Non-thyroidal illness
T4 replacement (sometimes
stablises with normal
TSH and FT4)
Normal
Some drugs
(anticonvulsants,anti
-T3, anti-T4)
Pituitary or hypothalamic
hypothyroidism,
Severe non-thyroidal
illness
Primary hyperthyroidism
Subclinical hyperthyroidism
Subtle T4 over replacement
Non-thyroidal illness
Pituitary or hypothalamic
hypothyroidism,
Severe non-thyroidal
illness
Thyroid Scale Diagram
 Optimal zone is an approximation and that it is meant to be
used as a rough guide.
Test
Lab Low
Optimal Range
Lab High
TSH
0.5
1.3-1.8
5.0
Free T4
0.8
1.2-1.3
1.8
Free T3
2.3
3.2-3.3
4.2
Cancer thyroid
• Thyroid carcinoma occurs relatively infrequently compared
to the common occurrence of benign thyroid disease
• Thyroglobulin Assays:
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Determines the amount of thyroid tissue after a thyroidectomy ie
there should be no thyroglobulin after complete thyroid gland
removal.
Used to monitor the recurrence of the common thyroid cancers
(follicular cell–derived tumors)
Tg measurements should always be interpreted in the context of
simultaneous measurement of Tg autoantibodies (TgAB). TgAB
occur in about 20% of thyroid cancer patients and can lead to
falsely low Tg measurements
• Calcitonin Assay:
Used to detect and monitor the recurrence of medullary thyroid
cancer
Patients Responsibilities
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Tell Your Doctor if You Have Symptoms
Ask Your Doctor for a TSH Test and Free T4 -- Make These
Tests as Part of Your Medical Routine if You Are a Woman
Over 35 or a man over 60 years
Take Your Medication as Directed
• Take Your Thyroid Medication Separately
from
Iron, Calcium and Multivitamins
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Do Not Change Brand or Dose of Your Thyroid Medication
Without Consulting Your Doctor
If Symptoms Persist or Return, Tell Your Doctor
Conclusion
• TSH is a good screening test to assess
thyroid function in an outpatient
setting. If TSH is abnormal, the
diagnosis is confirmed with thyroid
hormone levels.
• Screening for thyroid diseases
especially those at high risk is cost
effective as up to 20% of those with
subclinical thyroid disease may turn to
clinical thyroid disease
• Timing and choosing the right thyroid
test is the best approach in
understanding the meaning of the
results.