Common Endocrine Disorders

Gary L. Horowitz, MD Beth Israel Deaconess Medical Center

Boston, MA

Objectives

• Describe the typical laboratory values for TSH and Free T4 in hypo- and hyperthyroidism

• Explain the “cort stim test”

• Explain why “free testosterone” is the exception to the rule regarding the importance of free hormone levels

Assays to be Covered Today

• PTH • Cortisol • Thyroid Function Tests

• Estradiol & Testosterone • Pituitary

Themes

• “Normal” “Appropriate”

• Timing of Tests

• Stimulation/Suppression Tests

• Protein-Binding

Must be Something Wrong Here!

• Patient in OR for parathyroidectomy • Pre-op Dx = Hyperparathyroidism • Baseline PTH = 45 pg/ml, normal: 10-65 (45 ng/L, normal 10-65) • Could it be the correct patient? • Can the value possibly be correct?

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Two Dimensional Reference Intervals

Other PTH Issues

• N-terminal vs. C-terminal vs. Intact

• Rationale for Intra-Operative PTH • Rapid T1/2 (of Intact) • Suppression of Remaining Glands

don’t close until you’ve got the right one! re-operations 20% 5% chemistry trumps Anatomic Pathology??

Cortisol

• Chemical structure

• Diurnal variation

• CBG (Cortisol Binding Globulin) issues • UFC (urinary free cortisol) for cortisol excess states

Burtis CA, Ashwood ER. Tietz Fundamentals of Clinical Chemistry. 4th Edition. 1996.

Steroid Hormone Pathways

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Diurnal Variation of Cortisol

Cortisol Deficiency

• Causes • 10: Addison’s: vascular, infectious • 20: Pituitary (ACTH deficiency): tumor • 30 : Hypothalamic (CRH deficiency): iatrogenic

• Important to distinguish 1o vs 2o/3o

Cortisol Deficiency Laboratory Diagnosis

• Suspect with low peak (8am) cortisol

• Confirm with • ACTH level not practical

Burtis CA, Ashwood ER. Tietz Textbook of Clinical Chemistry. 3rd Edition. 1999.

Cortisol Deficiency Laboratory Diagnosis

• Suspect with low peak (8am) cortisol

• Confirm with • ACTH level not practical • Cosyntropin (ACTH analogue) Stimulation Test

– measure baseline + 30-minute cortisol – “normal” response:

» >7 ug/dL increase over baseline, or » absolute value >18 ug/dL (before or after dose)

(497 nmol/L)

Burtis CA, Ashwood ER. Tietz Textbook of Clinical Chemistry. 3rd Edition. 1999.

Cosyntropin (ACTH analogue) Stimulation Test

Cortisol Excess Semantics

• Cushing’s Syndrome versus Disease

– Syndrome

• excess cortisol, from any cause

– Disease • one specific cause: ACTH-secreting pituitary adenoma

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Breakdown of Causes of Cushing’s Syndrome

Cortisol Excess Laboratory Diagnosis

• Suspect with high nadir (4-8pm) cortisol – many false positives

» Stress » Obesity, especially in women with PCO » Depression

• Confirm with – Dexamethasone Suppression Test

• Potent glucocorticoid (less is used) • Little cross-reactivity with cortisol immunoassays

– vs Urinary Free Cortisol (UFC)

Rationale for UFC

• When serum cortisol exceeds CBG – serum level increases gradually – urine level increases abruptly

• free (unlike bound) cortisol is filtered

• Also, 24o-urine has integrating power – diurnal variation dilemma eliminated

Increased Diagnostic Power of Urine

05

1015202530354045

0 2 4 6

Increasing Incremental Amount of Cortisol

Cortisol Excess Laboratory Diagnosis

• Suspect with high nadir (4-8pm) cortisol – many false positives

» Stress » Obesity, especially in women with PCO » Depression

• Confirm with – Dexamethasone Suppression Test

• Potent glucocorticoid (less is used) • Little cross-reactivity with cortisol immunoassays

– vs Urinary Free Cortisol (UFC) – vs Serum Free Cortisol ??? – vs Midnight Salivary Cortisol ???

Thyroid Hormones (and their precursors)

Burtis CA, Ashwood ER. Tietz Fundamentals of Clinical Chemistry.4th Edition. 1996.

Common Thyroid Disorders

• Hypothyroidism • Subclinical Hypothyroidism

• Hyperthyroidism • Sick Euthyroid Syndrome

Thyroid Function Tests (TFTs)

• Useful • TSH (concept of generation) • FreeT4 (not all FreeT4 assays are good)

• Useless • Total T4 • T-uptake • T3 • Reverse T3

Thyroid Hormone Physiology

• Most T4 is deiodinated peripherally to T3

• T4 serves as reservoir for active hormone, T3

• Acute illness/stress causes T4rT3

Thyroid Hormone Binding Issues

• 99.97% of T4 is protein-bound! • 0.03% is free

• wide variations in binding protein concentrations

• wide variations in Total T4 (but not FreeT4) • e.g., pregnancy

Paradigm for Thyroid Disease

• Check TSH: – Should be high in hypothyroidism (>5.0 mIU/L)

• Has always worked well

– Should be low in hyperthyroidism (<0.3 mIU/L) • Until recently (3rd Gen TSH), has not worked well • So, need to assess T4 (or FreeT4): should be high

Analytic Sensitivity • How low can you measure reliably?

(Is there a little bit there, or is it 0?) • tumor markers & recurrence • TSH, too

• Two major definitions • ± 2 SD of 0-calibrator (or of negative sample)

– “analytic sensitivity” • level at which inter-assay CV rises above 20%

– “functional sensitivity”

What Do Those TSH Generations Mean?

Answer: Better Precision at Lower Concentrations 27

Historical Perspective

• Measure Total T4 (easy) • Correct Total T4 for Binding Proteins

• Measure T-uptake (original assay=“Resin T3-Uptake”) • Or Measure TBG by immunoassay • correct T4 by this amount

• Estimating the FreeT4 this way is: “like counting the number of cows on a field by

counting the number of feet and dividing by 4” James D. Faix, MD

• Why not just measure the FreeT4?

Free T4 “Measurements”

• Difficult to measure 0.03% of anything! • Estimated

• Resin T3-Uptake (RIA) • Automated T-Uptake • Measured TBG

• Measured • Equilibrium Dialysis (the gold standard) • Automated Analogue Tests

– 1-step – 2-step

(1o) Hypothyroidism [By Definition, Elevated TSH]

• Often, FreeT4 is low (as expected) • Sometimes, FreeT4 is normal!

• “subclinical hypothyroidism” • clinical significance:

– Should we wait until people are frankly hypothyroid? – Should we screen asymptomatic people?

» prevalence is high (women older than 40) » hypercholesterolemia, lack of energy, etc.

– Recent data: screening probably not indicated (but we do 350 TSHs/day on outpatients!)

(1o) Hyperthyroidism [By Definition, Low TSH]

• in true hyperthyroidism, TSH should be “undetectable” <0.05 (shades of “normal” PTH)

• sometimes, it’s low but “detectable” (>0.05 mIU/L) • “Sick Euthyroid Syndrome” • TSH is low, but detectable because FreeT4 is normal (not high)

• Solution: Measure FreeT4 (well) • Other lessons:

– don’t do TFTs on sick patients (unless thyroid is thought to be central issue)

Common Thyroid Disorders Laboratory Diagnosis

• Elevated TSH Check FreeT4

• Low FT4 Hypothyroidism [TSH >10.0] • Normal FT4 Subclinical Hypothyroidism [TSH 5.0-10.0]

• Low TSH Check FreeT4

• High FT4 Hyperthyroidism [TSH<0.05] • Normal FT4 Sick Euthyroid Syndrome [TSH 0.05-0.3] vs Subclinical Hyperthyroidism

A Few Slides on Androgens/Estrogens

(Time Permitting)

Testosterone Terminology

• Testosterone • Total = Free + SHBG-bound + Albumin-Associated • In contrast to cortisol and T4,

Free Testosterone is not the best indicator

• Rather, “Bioavailable Testosterone” =Total – SHBG-bound

= Albumin-Associated + Free ~ Albumin-Associated >> Free)

• Appears that Free T is 10% of total and 50% of bioavailable T

• In fact, it’s just 1% of total and 5% of bioavailable T

• To extent that Free T is in equilibrium with bioavailable T, Free T may be acceptable to use in place of bioavailable T

1488 ng/dL (51.6 nmol/L)

15 ng/dL ( 1% of total) 312 ng/dL (30% of total)

Testosterone Fractions (and misleading lab reports)

35

Proper Ordering of Free Testosterone

• Expert recommendations: – For men: nmol/L

• Total T <100: No further testing needed <3.47 • Total T 100 - 300: Free T or Bioavailable T 3.47-10.4 • Total T 300-1000: Normal 10.4 -34.7 • Total T >1000: No further testing needed >34.7

– For women: • Total T < 80: No further testing needed <2.78 • Total T > 80: Free or Bioavailable T >2.78

36

Free Testosterone • Several methods in use:

– Analogue immunoassay – Mass spectrometry – Calculated from Total T, SHBG, and albumin:

De Ronde W et al Clin Chem 2006;52:1777-1784

• NB: Testosterone is exception to the rule: – “free hormone” is not really the most important parameter – rather, “bioavailable” (= Free T + Albumin-T = Total T – SHBG-T)

37

Hirsutism in Women

• Two sources of androgens in women – Ovaries: testosterone + DHEA-SO4 – Adrenals: DHEA-SO4

• Don’t forget about DHEA-SO4!

Hormones Associated with the Menstrual Cycle

Menopause: Laboratory Diagnosis?

• When ovaries stop functioning, – Estradiol (E2) levels fall

• How low is “undetectable”? • analytic sensitivity (again)

– FSH/LH levels rise

• Does low E2 + high FSH/LH = menopause? • No! Menopause is a clinical diagnosis

Pituitary Hormones

• Posterior • Oxytocin • ADH

• Anterior • ACTH Cortisol • TSH T4 ( T3) • FSH/LH Estradiol & Testosterone • PRL

– macroprolactin: a “big” issue in PRL testing

• GH

Self-Assessment Question 1

Which of the following represents typical hypothyroidism? A) High TSH, High Free T4 B) High TSH, Low Free T4 C) Low TSH, High Free T4 D) Low TSH, Low Free T4

Self-Assessment Question 2

Which of the following is a reasonable screening test for Cushing’s syndrome? A) A low serum cortisol at night B) A low serum cortisol in the morning C) A high serum cortisol at night D) A high serum cortisol in the morning

Self-Assessment Question 3

When screening men for hypogonadism, which one of the following results is ambiguous and requires an additional chemistry test (e.g., SHBG)? A) A total serum testosterone 90 ng/dL (3.12 nmol/L) B) A total serum testosterone of 250 ng/dL (8.68 nmol/L) C) A total serum testosterone of 500 ng/dL (17.4 nmol/L) D) A total serum testosterone of 800 ng/dL (27.8 nmol/L)

Answers

1 (B) High TSH, Low Free T4 2 (C) A high serum cortisol at night 3 (B) A total serum testosterone of 250 ng/dL (8.68 nmol/L)