CASE ECASE E

HyperthyroidismHyperthyroidism

Poonam ShresthaPoonam Shrestha Veronica NouVeronica Nou Mary TormeyMary Tormey

Ainsley MacdonaldAinsley Macdonald

Mr TF, aged 50 years, has a history of Mr TF, aged 50 years, has a history of asthma and CAL. He has recently asthma and CAL. He has recently been hospitalised for a severe chest been hospitalised for a severe chest infection. He has also lost 5kg in infection. He has also lost 5kg in weight in the last 3 months, has weight in the last 3 months, has tachycardia of 120/min and fine tachycardia of 120/min and fine tremor(hands). He is currently tremor(hands). He is currently receiving prednisolone 25mg daily & receiving prednisolone 25mg daily & ceftriaxone 1g dailyceftriaxone 1g daily

Thyrotoxicosis is Thyrotoxicosis is suspectedsuspected

Effect of prednisolone on Effect of prednisolone on thyroid functionthyroid function

Glucocorticoid groupGlucocorticoid group Decrease TSH secretionDecrease TSH secretion Large dose Large dose decrease serum T3 decrease serum T3

concentrationconcentration Long term glucocorticoid Long term glucocorticoid

therapytherapydecrease in serum thyroid decrease in serum thyroid binding globulin(TBG)binding globulin(TBG)slight slight decrease of T4 concentrationdecrease of T4 concentration

Thyrotoxicosis vs asthma Thyrotoxicosis vs asthma and CALand CAL

Thyrotoxicosis can worsen asthma Thyrotoxicosis can worsen asthma and CALand CAL

Increase frequency and severity of Increase frequency and severity of asthma attackasthma attack

Increase requirement for medicationIncrease requirement for medication Asthma attacks improve in an Asthma attacks improve in an

euthyroid stateeuthyroid state

Possible causePossible cause

Reactive oxygen species due to Reactive oxygen species due to hyperthyroidism may be the hyperthyroidism may be the contributing factor in exacerbating contributing factor in exacerbating asthmaasthma

Reactive oxygen speciesReactive oxygen species Induce an autonomic imbalance between Induce an autonomic imbalance between

muscarinic receptor-mediated contraction muscarinic receptor-mediated contraction and the beta-adrenergic-mediated and the beta-adrenergic-mediated relaxation of the pulmonary smooth relaxation of the pulmonary smooth musclemuscle

Induce bronchoconstrictionInduce bronchoconstriction Elevate mucus secretionElevate mucus secretion Microvascular leakageMicrovascular leakage These conditions worsens the respiratory These conditions worsens the respiratory

conditions.conditions.

WHAT CLINICAL WHAT CLINICAL CHEMISTRY CHEMISTRY

TESTS SHOULD BE TESTS SHOULD BE PERFORMED TO PERFORMED TO

RULE OUT RULE OUT HYPERTHYROIDISHYPERTHYROIDIS

M & WHY?M & WHY?

HYPERTHYROIDISM?HYPERTHYROIDISM?

An elevation of free T4 An elevation of free T4 An elevation of free T3 An elevation of free T3 A very low TSHA very low TSH fine tremor (hands)fine tremor (hands) tachycardiatachycardia weight lossweight loss These are diagnostic signs & classic These are diagnostic signs & classic

symptoms of hyperthyroidismsymptoms of hyperthyroidism

Hyperthyroidism?Hyperthyroidism?

Measurement of serum Thyrotropin - Measurement of serum Thyrotropin - Thyroid Stimulating Thyroid Stimulating Hormone is considered the initial Hormone is considered the initial screening test in distinguishing screening test in distinguishing hyperthyroid and primary hyperthyroid and primary hypothyroid states from euthyroid hypothyroid states from euthyroid statesstates

A suppressed TSH is the cornerstone of diagnosis A suppressed TSH is the cornerstone of diagnosis of hyperthyroidism however, its secretion is of hyperthyroidism however, its secretion is influenced by many factors other than the influenced by many factors other than the negative feed back inhibition by t3 or t4 negative feed back inhibition by t3 or t4 bmj bmj 2000;320:1332-13342000;320:1332-1334

For example TSH can be reduced by fasting, For example TSH can be reduced by fasting, glucocorticoids -exogenous & endogenous, stress, glucocorticoids -exogenous & endogenous, stress, nonthyroidal illness, & false negative resultsnonthyroidal illness, & false negative results

In the presence of the above the specificity of se In the presence of the above the specificity of se TSH as a screening test is greatly reduced.TSH as a screening test is greatly reduced.

Hyperthyroidism?Hyperthyroidism?

In at least 90% of patients with In at least 90% of patients with hyperthyroidism T4 & T3 are elevatedhyperthyroidism T4 & T3 are elevated

In 5% of hyperthyroid patients T3 is In 5% of hyperthyroid patients T3 is exclusively elevated.exclusively elevated.

In developing hyperthyroidism fT4 & fT3 In developing hyperthyroidism fT4 & fT3 are elevated before tT4 & tT3are elevated before tT4 & tT3

Increased fT4 & decreased TSH is seen in Increased fT4 & decreased TSH is seen in conditions other than hyperthyroidism conditions other than hyperthyroidism therefore need to measure fT3 as well therefore need to measure fT3 as well

changes in TSH, T3 & T4 during systemic changes in TSH, T3 & T4 during systemic illness are poorly understood illness are poorly understood bmj 2000;320:1332-1334bmj 2000;320:1332-1334

In very ill patients both T3 &T4 (free & total) In very ill patients both T3 &T4 (free & total) are suppressedare suppressed

Free hormone assays are preferable to total Free hormone assays are preferable to total levels as there is decreased protein binding levels as there is decreased protein binding of thyroid hormone - relevant to this patient : of thyroid hormone - relevant to this patient :

acute severe illness,acute severe illness, protein malnutrition protein malnutrition with the ingestion of steroidswith the ingestion of steroids

Free T3 index levels can be measured to Free T3 index levels can be measured to compensate for altered binding levels compensate for altered binding levels

These levels are derived from the total These levels are derived from the total hormone levels & measurement of the hormone levels & measurement of the distribution of radiolabelled t3 between distribution of radiolabelled t3 between unoccupied protein binding sites in the sample unoccupied protein binding sites in the sample and an absorbent resin and an absorbent resin

Expect Free Thyroxine Index decreased in NTI Expect Free Thyroxine Index decreased in NTI & steroid administration.& steroid administration.

Expect Reverse T3 normal / increased in NTIExpect Reverse T3 normal / increased in NTI

Very systemically ill Patients with Very systemically ill Patients with low T4 levels have a poor low T4 levels have a poor prognosis/high morbidityprognosis/high morbidity

TFTs cannot be interpreted in TFTs cannot be interpreted in patients with systemic illness patients with systemic illness bmj bmj 2000;320:1332-13342000;320:1332-1334

Doing more indiscriminate Doing more indiscriminate biochemical tests will lead to biochemical tests will lead to confusion not clarity confusion not clarity bmj 2000;320:1332-1334bmj 2000;320:1332-1334

Significant false positive & negative TFT Significant false positive & negative TFT results seen in the presence of NTI as well results seen in the presence of NTI as well as during the administration of glucorticoidsas during the administration of glucorticoids

Repeat TSH, fT3 & fT4 after recovery from Repeat TSH, fT3 & fT4 after recovery from systemic illness.systemic illness.

TSH can remain suppressed for months TSH can remain suppressed for months after starting treatment for hyperthyroidism after starting treatment for hyperthyroidism even when T4 & T3 are normaleven when T4 & T3 are normal

Prolonged Prolonged thyrotoxicosis can thyrotoxicosis can

cause a number of non-cause a number of non-specific biochemical specific biochemical

abnormalitiesabnormalitiesoxford textbook of medicine oxford textbook of medicine

20032003 Abnormal LFTsAbnormal LFTs HypercalcuriaHypercalcuria Elevated levels of serum ferritinElevated levels of serum ferritin less common -less common - se calcium & phosphate raisedse calcium & phosphate raised glucose intolerance glucose intolerance microcytic aneamia or thrombocytopeniamicrocytic aneamia or thrombocytopenia

How to measure How to measure Total and Free Total and Free

T3?T3?

OverviewOverview

Over 99% of Triiodothyronine (T3) circulates Over 99% of Triiodothyronine (T3) circulates in blood bound to carrier proteins: in blood bound to carrier proteins: thyroxine- binding globulins (TGB)thyroxine- binding globulins (TGB)

Only the free (unbound) portion of T3 is Only the free (unbound) portion of T3 is responsible for its biological action. responsible for its biological action.

The concentration of the carrier proteins The concentration of the carrier proteins may be altered but the total concentration of may be altered but the total concentration of T3 will change so that the concentration of T3 will change so that the concentration of free T3 wil stay relatively constant.free T3 wil stay relatively constant.

Overview (2)Overview (2)

Thus, the concentration of free T3 Thus, the concentration of free T3 correlates more reliabily than total correlates more reliabily than total T3 levels. T3 levels.

Serum T3 measurement has little Serum T3 measurement has little specificity or sensitivity for specificity or sensitivity for diagnosing hypothyroidism, since diagnosing hypothyroidism, since enhanced T4 to T3 conversion enhanced T4 to T3 conversion maintains normal T3 concentrations maintains normal T3 concentrations until hypothyroidism becomes severe. until hypothyroidism becomes severe.

Approaches to the Approaches to the measurement of total measurement of total

and free T3.and free T3. Physical techniques:Physical techniques: Equilibrium Equilibrium

Dialysis, Ultrafiltration and Gel Dialysis, Ultrafiltration and Gel FiltrationFiltration OROR

Assay or Index ApproachesAssay or Index Approaches:: EstimateEstimate the free hormone the free hormone concentration in the presence of concentration in the presence of protein-bound hormone. protein-bound hormone.

Equilibrium DialysisEquilibrium Dialysis

Separates bound from free hormone. Separates bound from free hormone. Time-consuming, expensive, technically Time-consuming, expensive, technically

demanding and unavailable in most commercial demanding and unavailable in most commercial laboratories. laboratories.

Measuring serum free TMeasuring serum free T3 3 using overnight using overnight equilibrium dialysis of serum containing equilibrium dialysis of serum containing 125125I-TI-T33

The percentage of free TThe percentage of free T33 is calculated by is calculated by determining the total counts in the dialysate determining the total counts in the dialysate divided by the total divided by the total 125125I-TI-T33 added to the serum added to the serum multiplied by the total Tmultiplied by the total T3 3 concentration.concentration.

Index / ImmunoassaysIndex / Immunoassays

The free hormone methods used by most The free hormone methods used by most clinical laboratories (indexes and clinical laboratories (indexes and immunoassays) do not employ physical immunoassays) do not employ physical separation of bound from free hormone and separation of bound from free hormone and do not measure free hormone concentrations do not measure free hormone concentrations directly! directly!

These tests are typically binding protein These tests are typically binding protein dependent to some extent and should more dependent to some extent and should more appropriately be called appropriately be called "Free Hormone "Free Hormone Estimate"Estimate" tests, abbreviated FT4E and tests, abbreviated FT4E and FT3E.FT3E.

Index Methods: FT4I and Index Methods: FT4I and FT3IFT3I

Require two separate measurements:Require two separate measurements:1. One test is a total hormone 1. One test is a total hormone

measurement (TT4 or TT3) the othermeasurement (TT4 or TT3) the other 2. Is an assessment of the thyroid 2. Is an assessment of the thyroid

hormone binding protein hormone binding protein concentration using either an concentration using either an immunoassay for TBG or a T4 or T3 immunoassay for TBG or a T4 or T3 "uptake" test called a Thyroid "uptake" test called a Thyroid Hormone Binding Ratio (THBR).Hormone Binding Ratio (THBR).

Indexes Using a Thyroid Indexes Using a Thyroid Hormone Binding Ratio Hormone Binding Ratio (THBR) or "Uptake" Test(THBR) or "Uptake" Test

"Classical" uptake tests add a "Classical" uptake tests add a tracetrace amount of radiolabeled T3 or T4 to the amount of radiolabeled T3 or T4 to the specimen and allow the labeled specimen and allow the labeled hormone to distribute across the thyroid hormone to distribute across the thyroid hormone binding proteins in exactly the hormone binding proteins in exactly the same way as endogenous hormone.same way as endogenous hormone.

The distribution of the tracer is The distribution of the tracer is dependent upon the saturation of the dependent upon the saturation of the binding proteins. binding proteins.

Indexes ctd.Indexes ctd.

The free TThe free T33 index is then calculated index is then calculated using the total Tusing the total T33 and the TBG level. and the TBG level.

The index is directly proportional to The index is directly proportional to the free Tthe free T33 level. level.

ImmunoassaysImmunoassays

The two most commonly used The two most commonly used methods are a two-step and a one-methods are a two-step and a one-step immunoassay method. step immunoassay method.

These assays are not completely free These assays are not completely free of the influence of binding proteins of the influence of binding proteins or substances in serum that may or substances in serum that may result in false increases or decreases result in false increases or decreases in the free Tin the free T4 / 34 / 3 levels levels

Two Step ImmunoassayTwo Step Immunoassay

Two-step assays use a physical Two-step assays use a physical separation of free from protein-separation of free from protein-bound hormone before free hormone bound hormone before free hormone is measured by a sensitive is measured by a sensitive immunoassay, or alternatively, an immunoassay, or alternatively, an antibody is used to immunoextract a antibody is used to immunoextract a proportion of ligand out of the proportion of ligand out of the specimen before quantitation.specimen before quantitation.

One Step ImmunoassayOne Step Immunoassay

One-step ligand assays attempt to One-step ligand assays attempt to quantify free hormone in the quantify free hormone in the presence of binding proteins.presence of binding proteins.

Important to maintain free to Important to maintain free to protein- bound equilibrium.protein- bound equilibrium.

Solid Phase competitive Solid Phase competitive ELISA.ELISA.

The samples, assay buffer and T3 enzyme The samples, assay buffer and T3 enzyme conjugate are added to the wells coated with conjugate are added to the wells coated with anti- T3 monoclonal antibody. anti- T3 monoclonal antibody.

FT3 in the patients serum competes with a T3 FT3 in the patients serum competes with a T3 enzyme conjugate for the binding sites.enzyme conjugate for the binding sites.

Unbound enzyme conjugate is washed off by Unbound enzyme conjugate is washed off by washing with buffer. washing with buffer.

Upon the addition of the substrate, the intensity Upon the addition of the substrate, the intensity of the colour is inversely proportional to the of the colour is inversely proportional to the concentration to the FT3concentration to the FT3

The Application Of The Application Of Total And Free T3 Total And Free T3

Levels In Levels In Evaluation Of Evaluation Of Patient StatusPatient Status

Total And Free T3Total And Free T3

Only 0.3% of the total T3 is freely available. Only 0.3% of the total T3 is freely available.

Most of the T3 in circulation is bound to and Most of the T3 in circulation is bound to and transported by TBGtransported by TBG (thyroxine binding globulin). (thyroxine binding globulin). Therefore abnormalities in levels of TBG can cause Therefore abnormalities in levels of TBG can cause

erroneous results in total and free T3. erroneous results in total and free T3. Excess or lower TBG levels can be passed down as a Excess or lower TBG levels can be passed down as a

hereditary trait. It causes no problems aside from causing hereditary trait. It causes no problems aside from causing false test increases or decreases in thyroid hormones. false test increases or decreases in thyroid hormones.

People with this trait are often diagnosed as having a People with this trait are often diagnosed as having a thyroid dysfunction in the absence of any real problem or thyroid dysfunction in the absence of any real problem or need for treatment.need for treatment.

Serum free T3 levels are generally considered Serum free T3 levels are generally considered more reliable more reliable as they are less affected by as they are less affected by

carrier proteins (as the free T3 concentration is carrier proteins (as the free T3 concentration is preserved by equilibrium.)preserved by equilibrium.)

Smaller amounts of Smaller amounts of T3 T3 are bound to albumin and are bound to albumin and prealbumin. prealbumin.

Normal LevelsNormal Levels Total T3: 80-180 ng/dl (nanograms/decilitre)Total T3: 80-180 ng/dl (nanograms/decilitre) Free T3: 230-619 pg/dl (picograms/decilitre)Free T3: 230-619 pg/dl (picograms/decilitre)

Measurement of Serum Thyroid HormonesMeasurement of Serum Thyroid Hormones

an indicator of thyroid function. an indicator of thyroid function. The most frequently used test is T4 by radioimmunoassay. The most frequently used test is T4 by radioimmunoassay.

This is referred to as a T7 This is referred to as a T7 meaning that a resin T3 uptake or RT3u has been done to meaning that a resin T3 uptake or RT3u has been done to

correct for certain medications such as birth control pills, correct for certain medications such as birth control pills, other hormones, seizure medication, cardiac drugs, or even other hormones, seizure medication, cardiac drugs, or even aspirin that may alter the routine T4 test. aspirin that may alter the routine T4 test.

The T4 reflects the amount of thyroxine in the blood. The T4 reflects the amount of thyroxine in the blood. If the patient does not take any type of thyroid If the patient does not take any type of thyroid medication, this test is usually a good measure of medication, this test is usually a good measure of thyroid function. thyroid function.

However thyroxine (T4) only represents 80% of However thyroxine (T4) only represents 80% of thyroid hormone produced. thyroid hormone produced.

The other 20% is tri-iodothyronine or T3. T3 The other 20% is tri-iodothyronine or T3. T3 levels are levels are elevated in most patients with thyroid dysfunction and are elevated in most patients with thyroid dysfunction and are therefore unreliable as an exclusive screen. therefore unreliable as an exclusive screen.

T3 may be measured in T3 may be measured in cases where there is some doubt cases where there is some doubt about whether the patient has hyperthyroidism or about whether the patient has hyperthyroidism or hypothyroidism after measuring T4 and RT3u.hypothyroidism after measuring T4 and RT3u. where symptoms of hyperthyroidism are apparent but the where symptoms of hyperthyroidism are apparent but the

thyroid gland is still producing normal levels of T4. thyroid gland is still producing normal levels of T4.

They are also used to monitor response to therapy.They are also used to monitor response to therapy.

Therefore T3 is measured as part of a thyroid function Therefore T3 is measured as part of a thyroid function evaluation to provide a more accurate picture.evaluation to provide a more accurate picture.

T3 ElevationT3 Elevation

Greater-than-normal levels may indicate:Greater-than-normal levels may indicate: Hyperthyroidism (e.g., Graves’ disease) Hyperthyroidism (e.g., Graves’ disease)

Serum T3 elevation parallels serum T4 in 90-95% Serum T3 elevation parallels serum T4 in 90-95% of casesof cases

Isolated serum T3 elevation in ~ 5% of casesIsolated serum T3 elevation in ~ 5% of cases T3 thyrotoxicosis (rare)T3 thyrotoxicosis (rare)

Isolated T3 elevationIsolated T3 elevation Thyroid Cancer (rare)Thyroid Cancer (rare) ThyroiditisThyroiditis

T3 ReductionT3 Reduction

Lower-than-normal levels may indicate: Lower-than-normal levels may indicate: - Chronic illness- Chronic illness- Hypothyroidism (e.g., Hashimoto’s disease)- Hypothyroidism (e.g., Hashimoto’s disease)

- Starvation- Starvation

Other Factors That May Affect T3 MeasurementOther Factors That May Affect T3 Measurement

Drugs that can increase T3 measurements include:Drugs that can increase T3 measurements include:- clofibrate, estrogens, methadone, and oral - clofibrate, estrogens, methadone, and oral contraceptives.contraceptives.

Drugs that can decrease T3 measurements include:Drugs that can decrease T3 measurements include:- anabolic steroids, androgens, antithyroid drugs (for - anabolic steroids, androgens, antithyroid drugs (for example, propylthiouracil), lithium, phenytoin, and example, propylthiouracil), lithium, phenytoin, and propranolol.propranolol.