Download Investigation of Thyroid Disease

Investigation of
Thyroid Disease
Two Hormones ‐ T3 & T4
T4‐Only thyroidal source
Thyroid Physiology
T3‐20% from thyroid secretion
80% from T4 in other tissues
> 99% protein – bound hormones
FT4‐0.05%
FT3‐0.5%
Reverse T3
Thyroid Regulation
Stimulation by TSH
Negative feed‐back.
TSH under TRH control
Thyroid Hormone Estimation
(1)T3, T4, FT3, FT4 & TSH.
Radio‐immunoassay
ELISA
Chemiluminiscence
(2)Binding ratio (Resin uptake)
(3)TBG level
Why Free hormone levels?
Metabolically active forms
Not affected by binding protein disorders.
TBG excess ‐ Estrogen therapy, pregnancy, hepatitis, congenital.
Low TBG ‐ Androgen therapy, chronic liver disease.
Thyroid Stimulating Hormone
Single best test for thyroid disease.
When T3 & T4 are high‐TSH is low.
When t3 & T4 are low ‐ TSH is high
Use of TSH level ‐ Diagnosis & follow ‐ up of thyroid dysfunction.
TRH Stimulation Test.
Best Assays To Order
TSH
FT4
T3 if T3 toxicosis is suspected.
TFT Patterns
T3
T4
TSH
Diagnosis
Low low
high Primary hypothyroidism
Low low
low
Pituitary hypothyroidism
High high
low Hyperthyroidism
High high
high
TSH secreting tumour
Resistance to Thyroid hormones
Antithyroid Antibodies
Inhibiting antibodies:
TMA or TPO antibody
Anti‐thyroglobulin antibody
In Hashimotos Thyroiditis ‐
TMA + ve in 95%
TGA + ve in 55%
TPO + ve ‐ future hypothyroidism
Stimulating Antibodies
Thyroid Stimulating Immunoglobulins
Positive in Graves disease
Measured by c‐AMP production by Graves serum In thyroid cells
Useful in predicting neo ‐ natal thyrotoxicosis
Thyroglobulin
Found in colloid
Site of T3 & T4 synthesis.
High TG – Hyperthyroidism
Thyroiditis
Smoking
Low TG‐Athyreosis
Use of TG estimation – Follow ‐ up of thyroid cancers
Radioactive Iodine Uptake
Thyroid gland concentrates Iodine
Normal – 25 % after 24 hours
Use ‐ in thyrotoxicosis only ‐
High in Graves disease,toxic MNG, toxic solitary nodule.
Low in factitious thyrotoxicosis, sub ‐ acute & post ‐ partum thyroiditis
Iodine induced thyrotoxicosis
Thyroid Scan
I 123 or Technitium ‐ 99m
Use ‐ to assess function in thyroid nodules
Hot ‐ hyperfunctioning
Cold – non ‐ functioning
20 % malignant
Ultrasonography
1. Diagnostic‐For thyroid nodules
Benign‐anechoic,floating debris+‐ or hyperechoic
with eggshell calcification
Malignant ‐ Hypoechoic
Irregular margins
Microcalcification
2. Follow‐up Fine Needle Aspiration Cytology
Safe OP procedure.
90 – 95 % accurate
Useful in solitary nodule
Dominant nodule in MNG
Thyroiditis
? US guided
Calcitonin
From para ‐ follicular C cells
? physiological role
High in Medullary carcinoma,
MEN II
Use‐in families with MTC, MEN II
For early diagnosis & Follow ‐ up
Genetic studies