Investigations of Thyroid Disorders:

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Investigations of Thyroid Disorders:

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Friday, 11 December 2009 08:52

Investigations of Thyroid Disorders:
(A) Sleeping pulse:
Measurement of pulse rate when the patient sleeping i.e. unconscious to avoid psychological stress effect
Normally 70:80 beat/min.
Mild toxicity 80:90 beat/min.
Moderate toxicity 90:100 beat/min.
Severe toxicity >100 beat/min.
It is important for follow up the effect of antithyroid and B blockers given for control of thyrotoxic patient.
(B) Thyroid Function Tests:
(1) Estimation of T4 & free T4,T3 & free T3 and T.S.H by radio immunoassay.
The best test for 1ry hyperthyroid.
Ä Normal levels:
T4 ® (55 : 150 nmol/l). Free T4 ® (8:26 pmol/l).
T3 ® (1.2 : 3.1 nmol/l). Free T3 ® (3:9 pmol/l).
T.S.H ® up to 5 uU/l.
(2) T3 Resin uptake: In a test tube add Pnt. 's blood to ? Known amount of radio-active T3 then add resin.
Part of T3 fixed by plasma patient.
Free part. precipitated by resin.
In thyrotoxicosis all plasma patient is saturated,(cannot fix T3) T3 resin uptake will increase.
As it is in vitro test, there is no hazards of radiation.
(3) Free thyroxin index: As the results of T3 resin uptake is not accurate. This index is the result of correlation between T3 resin uptake and the total T3 & T4.
Free T4 index = Total serum T4 X 100 / T4 resin uptake.
Free T3 index = Total serum T3 X 100 / T3 resin uptake.
(4) TRH test : Injection of TRH in normal individuals will increase the level of TSH above the basal level. In thyrotoxic patients TSH is suppressed and will not increase. In hypotyroid patient TSH release is exaggerated. This test now used infrequently. It is of value if T4 and TSH levels are discrepant, in ophthalmic Graves' disease and to detect the cause of hypothyroidism whether thyroid or hypothalamic or pituitary disease.
(5) Protein bound iodine: "P.B.I"
· Old test, not accurate, depends on the fact that P.B.I with T3 & T4.
· It may give false high results in patients taking drugs containing iodine or after urography, as urograffin containing iodine.
· It may give false low results in patients with hypoproteinemia, as in nephritic syndrome, liver cirrhosis or nutritional hypoproteinemia.
(C) Radioactive Iodine Applications:
(1) Radioactive iodine uptake
Normal 30-70% of the given dose in 24 hs.
> 70% ® hyper function < 30% ® hypofunction
Precautions before the test is done:
For 3 weeks before avoid drugs containing I.
The patient must be free from G.I.T troubles as the I123 is given orally (25 u curies)
Its value now is deteriorating. It may help to differentiate thyrotoxicosis of hyperthyroidism with high iodine uptake from thyrotoxicosis of thyroiditis with low iodine uptake.
(2) Scintillation scan "Thyroid scanning"
Hot nodules = hyper function
Cold nodules = hypo function = suspicion of malignancy.
Worm nodule = normal function (does not appear on scanning and clinically felt)
D) Thyroid autoantibodies: ( To thyroid microsomes and thyroglobulin)
Significant titres are found in patients with autoimmune thyroiditis causing hyperthyroidism or hypothyroidism or an euthyroid goitre.
Ä Thyroid antibodies are:
1.Microsomal antibody ( its antigen present in the thyroid cytoplasm)
2.Thyroglobulin antibody. ( Antigen in the thyroid colloid )
3. Second colloid antibody ( Antigen in the thyroid colloid )
E) Investigations of the biochemical effects of hyperthyroidism:
1. Increase basal metabolic rate.
2. High cholesterol.
3. Glucosoria.
SOURCE: Prof. AYMAN SALEM'S BOOK
Copyright: (Vascular Society of Egypt ) & (Medical Educational web)
Not to be reproduced without permission of Vascular Society of Egypt

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