Diagnostic Biochemistry of Endocrine disorders

Question 1

Endocrine glands - Hormones

Answer 1

Question 2

Thyroid: … marker of choice

Answer 2

Thyroid: TSH marker of choice

• Very sensitive indicator of thyroid activity in target tissue
• TSH better index than FT4 in steady state
• Diagnosing primary hypothyroidism and primary hyperthyroidism - excellent test

Question 3

• 50 y F, tired, lethargy, night sweats, some weight loss
  
  • TSH <0.01 mU/L 0.3- 4.2
  • FT4 32 pmol/L 12- 22
  • FT3 9 pmol/L 3.1- 6.8

Answer 3

• TSH is undetectable
• FT4 is high
• FT3 is high
  
  • Thyrotoxicosis - if free T3 is high, confirm it is endogenous (thyroid gland itself)

Question 4

Signs of hyperthyroidism (CKS NICE)

Answer 4

• Agitation, fine tremor, warm moist skin, palmar erythema.
• Sinus tachycardia, atrial fibrillation, heart failure, peripheral oedema.
• Pruritus, urticaria, vitiligo, diffuse alopecia.
• Muscle wasting, proximal myopathy, hyper-reflexia.
• Splenomegaly, lymphadenopathy.
• Gynaecomastia in men.
• Extrathyroid manifestations of Graves’ (rare): thyroid acropachy, thyroid dermopathy.

Question 5

Signs of hyperthyroidism (CKS NICE)

• Thyroid enlargement (a …).
• …’ disease: diffusely symmetrically enlarged without nodules +/- bruit.
• Toxic … …: non-tender thyroid nodules
• Toxic …: unilateral, non-tender thyroid mass
• Subacute …: tender, firm, irregular, diffuse/asymmetric enlargement.
• …-induced thyroiditis: small goitre usually present.

Answer 5

• Thyroid enlargement (a goitre).
• Graves’ disease: diffusely symmetrically enlarged without nodules +/- bruit.
• Toxic multinodular goitre: non-tender thyroid nodules.
• Toxic adenoma: unilateral, non-tender thyroid mass.
• Subacute thyroiditis: tender, firm, irregular, diffuse/asymmetric enlargement.
• Amiodarone-induced thyroiditis: small goitre usually present.

Question 6

Additional Assessments in Hyperthyroidism

• TRAbs (TSH Receptor antibodies): if … suspected, or ….
• Inflammatory markers e.g. …: if thyroiditis suspected.
• TPOAbs (Thyroid peroxidase antibodies): if postpartum and postpartum thyroiditis is suspected.
• … and ..: if about to start anti-thyroid drugs.
• … of neck: if thyroid is enlarged or nodule identified.

Answer 6

• TRAbs (TSH Receptor antibodies): if Grave’s suspected, or pregnant.
• Inflammatory markers e.g. CRP: if thyroiditis suspected.
• TPOAbs (Thyroid peroxidase antibodies): if postpartum and postpartum thyroiditis is suspected.
• FBC and LFT: if about to start anti-thyroid drugs.
• USS of neck: if thyroid is enlarged or nodule identified.

Question 7

• 70 y, ileus and NSTEMI post Hartman’s
  
  • ​TSH 0.04 mU/L 0.3- 4.2
  • FT4 10 pmol/L 12- 22
  • FT3 1.1 pmol/L 3.1- 6.8

Answer 7

• ​TSH is suppressed but is inappropriately low - because FT4 and FT3 are both low
• FT4 low
• FT3 low
  
  • Could be hypopituitarism - however sick euthyroid more likely

Question 8

Sick euthyroid

• The body tries to avoid unnecessary … … when sick…
• Therefore you ‘switch off’ the … …, then switch on later (get a rebound high TSH trying to bring the T3 and T4 back up to normal).
• Basically any pattern is possible
• Therefore do not measure TFTS in sick people unless you are suspecting thyroidal illness e.g. myxoedema coma, new onset fast AF etc.

Answer 8

• The body tries to avoid unnecessary energy expenditure when sick…
• Therefore you ‘switch off’ the thyroid axis, then switch on later (get a rebound high TSH trying to bring the T3 and T4 back up to normal).
• Basically any pattern is possible
• Therefore do not measure TFTS in sick people unless you are suspecting thyroidal illness e.g. myxoedema coma, new onset fast AF etc.

Question 9

Other causes of abnormal TFTs (NICE CKS)

• Age : mild TSH … (4.0–7.0 mU/L) may be normal.
• Population: ranges should really be specific to … population.
• Pregnancy: physiological TSH suppression in the late … trimester.
• Hyperemesis gravidarum.
• Drugs: multiple e.g. TSH suppression with …, high-dose glucocorticoids, amphetamines, octreotide, and bromocriptine. A.. typically causes low TSH, high FT4 with high/normal FT3.
• Excess exogenous levothyroxine = … not hyperthyroidism.
• … interference: antibodies; biotin ingestion, and macroTSH.

Answer 9

• Age : mild TSH elevation (4.0–7.0 mU/L) may be normal.
• Population: ranges should really be specific to local population.
• Pregnancy: physiological TSH suppression in the late first trimester.
• Hyperemesis gravidarum.
• Drugs: multiple e.g. TSH suppression with dopamine, high-dose glucocorticoids, amphetamines, octreotide, and bromocriptine. Amiodarone typically causes low TSH, high FT4 with high/normal FT3.
• Excess exogenous levothyroxine = thyrotoxicosis not hyperthyroidism.
• Assay interference: antibodies; biotin ingestion, and macroTSH.

Question 10

… typically causes low TSH, high FT4 with high/normal FT3.

Answer 10

Amiodarone typically causes low TSH, high FT4 with high/normal FT3.

Question 11

• 31 F, rapid weight loss post gastric bypass​
  
  • TSH 3.2 mU/l 0.47-3.41
  • FT3 <0.5 pmol/L 3.6-5.7
  • FT4 7.6 pmol/L 9-19

Answer 11

• TSH 3.2 normal
• FT3 <0.5 very low
• FT4 7.6 low
  
  • Differentials:
  • Interference
  • Sick euthyroid/starvation (80-90% T3 is made by peripheral conversion which is stopped during starvation)

Question 12

• Pt tired, lethargy
  
  • ​TSH 86 mU/L 0.3 - 4.2
  • FT4 7 pmol/L 12 - 22
  • Diagnosis?
• Years later - well controlled, annual review:
  
  • TSH 86 mU/L 0.3 - 4.2
  • FT4 16 pmol/L 12 - 22
  • Diagnosis?

Answer 12

• TSH high
• FT4 low
  
  • Primary hypothyroidism
• TSH high
• FT4 normal
  
  • Non-concordance (taken on morning of blood test - so free T4 normal but TSH takes 6 weeks to bring down - not taken normally, could also be malabsorption, drug interference is less likely due to FT4 conc, analytical interference)

Question 13

• Pt tired, lethargy, weight gain​
  
  • TSH 9.0 mU/L 0.3 - 4.2
  • FT4 14 pmol/L 12 - 22

Answer 13

• TSH elevated, free T4 normal
• Symptoms will make the difference (or fertility/pregnancy)
• Equivocal or Borderline results
• Request TPO Ab – marker of chronic autoimmune thyroiditis – to confirm chronic autoimmune hypothyroidism

Question 14

• Pt tired, lethargy, weight gain
  
  • TSH 9.0 mU/L 0.3 - 4.2
  • FT4 12 pmol/L 12 - 22
  • TPO Ab 365 U/mL <35

Answer 14

• Currently those with subclinical hypothyroidism are recommended to be followed up (based on TPO result). This study suggests they don’t (only 2% of those with subclinical hypothyroidism became hypothyroid at 5 years, 64% remained the same, 40% reverted to normal). Br J Gen Pract. 2018;68(675):e718-26.

Question 15

Adrenals Cortisol: Cushing’s syndrome

• 23y F bends to tie a shoelace, intense low back pain, goes to A&E
• O/E:
  
  • Severe back pain in lumber region
  • Abdominal striae, G2P2
  • Pigmentation in palmer creases & gums
  • Proximal weakness

Answer 15

• High sodium, low potassium, metabolic alkalosis with high bicarb, slightly dehydrated? (high urea), hyperglycaemia
• X ray - crush fracture - L4 (only in her 20’s, usually osteoporosis)

Question 16

Actions of cortisol – mineralo-corticoid

• High cortisol mimics actions of aldosterone on kidney distal convoluted tubules
• Reabsorption Na+ + water
• Hypertension, raised Na
• Loss K+ + H+( increased HCO3-)
  
  • …kalaemic a…

Answer 16

• High cortisol mimics actions of aldosterone on kidney distal convoluted tubules
• Reabsorption Na+ + water
• Hypertension, raised Na
• Loss K+ + H+( increased HCO3-)
• Hypokalaemic alkalosis

Question 17

Once you identify Cushing’s syndrome, you need to identify if it is … dependent or … independent

Answer 17

Once you identify Cushing’s syndrome, you need to identify if it is ACTH dependent or ACTH independent

Question 18

Causes of Cushing’s Syndrome

• ACTH dependent:
  
  • ​Cushing’s .. (p…)
  • … ACTH-secreting tumour
• ACTH independent:
  
  • A..
  • C…
  • Nodular adrenal …
  • A… rest tumour
    *

Answer 18

• ACTH dependent:
  
  • ​Cushing’s disease (pituitary)
  • Ectopic ACTH-secreting tumour
• ACTH independent:
  
  • Adenoma
  • Carcinoma
  • Nodular adrenal hyperplasia
  • Adrenocortical rest tumour

Question 19

Cushing’s syndrome is caused by cushing’s disease (pituitary) what % of the time?

Answer 19

68%

Question 20

Problems with diagnosing Cushing’s Syndrome

• Biological:
  
  • … variation and s…
  • CVw 20.9%,CVg 45.6%
• Analytical:
  
  • Analyte homology, lower limit of …
• Pathological:
  
  • Cyclical … tumours
  • No … cut-off’s- false +ives/-ives
  • Mild vs p..

Answer 20

• Biological:
  
  • Diurnal variation and stress
  • CVw 20.9%,CVg 45.6%
• Analytical:
  
  • Analyte homology, lower limit of detection
• Pathological:
  
  • Cyclical adrenal tumours
  • No discreet cut-off’s- false +ives/-ives
  • Mild vs pseudo

Question 21

Diagnostic Tests for Cushing’s Syndrome: Aim

1. Identify spontaneous …
   * Mild vs pseudo-Cushing’s
2. Determine whether … dependent or independent
3. If … dependent localise source
   * It is essential to follow this order.

Answer 21

1. Identify spontaneous hypercortisolism
   * Mild vs pseudo-Cushing’s
2. Determine whether ACTH dependent or independent
3. If ACTH dependent localise source
   * It is essential to follow this order.

Question 22

Difficulties Diagnosing Cushings: J Clin Endocrinol Metab 2008;93:1526

Answer 22

Question 23

Tests for Cushing’s: 24 Hour Urine Free Cortisol

• Free – normally
• Free – not affected by drugs that affect .. .. .. (CBG), good sensitivity in … (89%)
• False +ive – obesity, depression, stress, alcoholism, drugs e.g. diuretics, high salt intake, high fluid intake
• False negatives in … (salivary better)

Answer 23

• Free – normally <2% of total secreted cortisol appears in urine. Diagnose Cushing’s if 4* ULN
• Free – not affected by drugs that affect cortisol binding globulin (CBG), good sensitivity in children (89%)
• False +ive – obesity, depression, stress, alcoholism, drugs e.g. diuretics, high salt intake, high fluid intake
• False negatives in cyclical (salivary better)

Question 24

Tests for Cushings: 1mg Dexamethasone Suppression Test

• 1mg dexamethasone 22:00-24:00 and blood test at…
• If
• Easy, out-patient, cheap.
• Compliance, absorption, metabolism of dexamethasone
• CBG
• False … – normal people, plus stress, obesity, infection, illness, alcohol, depression.

Answer 24

• 1mg dexamethasone 22:00-24:00 and blood test 8am
• If <40 nmol/L rule out Cushing’s; specific less sensitive
• Easy, out-patient, cheap.
• Compliance, absorption, metabolism of dexamethasone
• CBG
• False positives – normal people, plus stress, obesity, infection, illness, alcohol, depression.

Question 25

Tests for Cushings: Late Night Salivary Cortisol

• Related to free, easy to collect, analytically stable, avoids venepuncture-induced rises, out patient
• False … – poor DM control, obesity depression, stress, cigarettes, chewing tobacco, licorice
• … … disturbances (illness shifts) may also affect

Answer 25

• Related to free, easy to collect, analytically stable, avoids venepuncture-induced rises, out patient
• False positives – poor DM control, obesity depression, stress, cigarettes, chewing tobacco, licorice
• Circadian rhythm disturbances (illness shifts) may also affect

Question 26

Suspected Cushing’s Syndrome

Answer 26

Question 27

Confirmed Cushing’s Syndrome

Answer 27

Question 28

Basal ACTH concentrations in patients with spontaneous Cushing’s syndrome

• Normal/increased in …
• Low in …

Answer 28

• Normal/increased in ACTH dependent forms
• Low in adrenal

Question 29

Case: UGI bleed

• Background: month of tiredness, pins and needles, bad sleep, sore mouth, breathless and swelling
• MRI of her abdomen to look for terminal ileum disease (had a low B12)
• Liver lesions and lymph nodes, a CT showed no obvious primary
• Results shown - Venous gas:
  
  • pH was 7.56 on arrival (alkalosis)
  • Bicarb 29 (raised)
  • Lactate 3.3 mmol/L (really high)
  • thoughts?

Answer 29

• hypercortisolism or Primary aldosteronism (also called Conn’s syndrome)????
• Cushings?
• lactate high - due to…
• Lactic acid causes a metabolic acidosis however…*
• Phosphofructokinase is switched on by alkalosis and will double lactate production for a 0.3 rise in pH.*
• The liver has an ability to cope with increases in lactic acid by 10 fold so usually this production doesn’t cause lactate to accumulate….. This lady is known to have liver lesions*
• unable to metabolise lactate produced by alkalosis - suggests alkolosis is worse than pH suggests
• Further results:
• Na 141, K 2.4 and Cl 90 (Contraction alkalosis vs Cushings/Conn’s)*
• ALT 119*
• Urine potassium 30 mmol/L (<10 in hypokalaemia) - inappropriately high - so, dd is cushing’s or conn’s, or renal tubule damage?*
• Cortisol 1257, 1336, 1485, 1559 (23:15 – the others taken throughout the afternoon) high levels*
• ACTH received too late*
• Diagnosis shown

Question 30

What is a superior vena cava obstruction (SVCO)?

Answer 30

• The superior vena cava (SVC) is a large vein in the middle of the chest, behind the breast bone (sternum). It carries blood from the upper half of the body straight to the heart.
• Superior vena cava obstruction (SVCO) happens when something blocks the blood from flowing along the SVC. The walls of the SVC are thin. This means they easily become squashed (compressed).
• Most cases of SVCO are caused by an underlying lung cancer. The cancer itself may be pressing directly on the SVC, or it may have spread to the lymph nodes (glands) nearby, which become swollen.

Question 31

What is Metyrapone?

Answer 31

• Drug used to inhibit cortisol synthesis
• (Metyrapone is a competitive inhibitor of 11β-hydroxylation in the adrenal cortex; the resulting inhibition of cortisol (and to a lesser extent aldosterone) production leads to an increase in ACTH production which, in turn, leads to increased synthesis and release of cortisol precursors. - BNF)

Question 32

16 year old: 2-3 days of vomiting, nausea, lethargy

• PMH: well controlled IDDM
• Alert, orientated. Tanned
• Pulse 110, BP 110/56
• HS 1+2+nil
• Chest clear
• Abdo NAD
• Impression severe dehydration – not DKA
• DIAGNOSIS?

Answer 32

Diagnosis: Adrenal Insufficiency

Question 33

Primary Adrenal Insufficiency

Answer 33

Question 34

Secondary Adrenal Insufficiency

Answer 34

Question 35

Adrenal Insufficiency Investigation

Answer 35

Question 36

Random Cortisol – poor test:

• … variation (peak on awakening 8:00-10:00) – caution … workers, (nadir bedtime 00:00).
• … binding … – HRT and OCP (stop 6 weeks before)
• Analytical interference
• No clear … …
• … increases but … affect levels

Answer 36

• Diurnal variation (peak on awakening 8:00-10:00) – caution shift workers, (nadir bedtime 00:00).
• Cortisol binding globulin – HRT and OCP (stop 6 weeks before)
• Analytical interference
• No clear cut offs
• Stress increases but sickness affect levels

Question 37

Short Synacthen Test

• Patient preparation
  
  • Not in 1st 2 weeks after … surgery
  • Not on … (cross react in assay)
• How is it done?
  
  • 250 mcg IM or IV Synthetic … (…)
  • Take blood at … mins and … mins

Answer 37

• Patient preparation
  
  • Not in 1st 2 weeks after pituitary surgery
  • Not on steroids (cross react in assay)
• How is it done?
  
  • 250 mcg IM or IV Synthetic ACTH (synACTHen)
  • Take blood at 0 mins and 60 mins

Question 38

Short Synacthen Test - What do the Results mean?

• Normal test is a rise of cortisol over … nmol/l (assay dependent)
• Controversies currently
  
  • Dose to use in …
  • … of day of test
  • … … for a pass
  • … of synacthen is supraphysiological
  • False … if recent onset of secondary hypoaldosteronism (no adrenal atrophy)

Answer 38

• Normal test is a rise of cortisol over 550 nmol/l (assay dependent)
• Controversies currently
  
  • Dose to use in children
  • Time of day of test
  • Cut off for a pass
  • Dose of synacthen is supraphysiological
  • False positive if recent onset of secondary hypoaldosteronism (no adrenal atrophy)

Question 39

Other Dynamic Function Tests (DFTs), non-exhaustive

• Common:
  
  • Short … test
  • Overnight … suppression test
  • … deprivation test
• Rare:
  
  • … stress test
• Others:
  
  • Glucose tolerance test for …
  • Combined … function tests (GnRH/TRH/SST)
  • … fludrocortisone test
  • Prolonged …
  • Hypertonic … infusion
  • Oral … tolerance

Answer 39

• Common:
  
  • Short synacthen test
  • Overnight dexamethasone suppression test
  • Water deprivation test
• Rare:
  
  • Insulin stress test
• Others:
  
  • Glucose tolerance test for acromegaly
  • Combined pituitary function tests (GnRH/TRH/SST)
  • Furosemide fludrocortisone test
  • Prolonged fast
  • Hypertonic saline infusion
  • Oral glucose tolerance

Question 40

57 F yo, snoring - Diagnosis?

• GH 29.4 ug/l
• IgF1 164 nmol/l (6-36)
• FSH 60 u/l
• LH 14 u/l
• TSH 1.1 miu/l
• FT4 11.4 pmol/l
• Cortisol 298 nmol/l

Answer 40

GH and IgF1 in acromegaly:

• Secretion of GH is episodic the level of GH may fluctuate between undetectable to 30 µg/l
• IgF1 levels are persistently elevated
• High IgF1 may also be seen in pregnancy and late puberty
• A high IgF1 is highly specific for acromegaly and correlates with the disease activity

Question 41

Diagnosis of Acromegaly

• Oral … Tolerance Test:
  
  • 75g oral … + …
• Take GH and Glucose:
• 0, 30, 60, 90, 120 mins
• GH <0.4 microg/L = pass, raised GH may be seen in uncontrolled diabetes, malnutrition, renal failure, physical and emotional stress
• Nonetheless usually GH < 1 µg/l and in acromegaly > … µg/l.
• Failure to … = acromegaly

Answer 41

• Oral Glucose Tolerance Test:
  
  • 75g oral glucose + Fasting
• Take GH and Glucose:
• 0, 30, 60, 90, 120 mins
• GH <0.4 microg/L = pass, raised GH may be seen in uncontrolled diabetes, malnutrition, renal failure, physical and emotional stress
• Nonetheless usually GH < 1 µg/l and in acromegaly > 5 µg/l.
• Failure to suppress = acromegaly

Question 42

21 y.o. Road traffic collision - What test?

• Hit head on windscreen, suffered concussion
• 5 months later, complained of thirst and having to get up to pass urine
• Admits to getting up 4-5 times a night
• Drinking/passing up to 8 litres a day
  *

Answer 42

Water deprivation test

• Urine osmo barely concentrating, despite plasma osmolality and serum sodium increasing. Becoming dehydrated, but still passing large volumes of urine. Loosing the appropriate amount of weight.
• After DDAVP - they can drink water (not too much as can now become water overloaded).
• Urine output starts to fall, Urine osmolality starts to increase, Plasma osmolality starts to return to normal
• DIAGNOSIS = CRANIAL DIABETES INSIPIDUS

Question 43

Previous cranial surgery. Polyuria, polydipsia

• Since cranial surgery, had some problems with depression. Getting up to pass urine in night up to 4 times
• After these results below:
  
  • Urine volumes start to decrease and urine osmolality begins to rise

Plasma osmolality stays fairly constant. This is an appropriate response. Initially the test looked like diabetes insipidus, but eventually urine concentration kicked in - diagnosis?

Answer 43

Habit polygipsia

Question 44

62 yr old man on risperidone

• Prolactin 939 mU/L (73-407)
• Macroprolactin recovery 70%
• Macroprolactin Negative
• Conclusion: …

Answer 44

Conclusion: DA antagonist; DDx pituitary adenoma