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Lab Diagnostics > 14 - Endocrinology > Flashcards

14 - Endocrinology Flashcards

1
Q

HYPOTHYROIDISM IN DIFFERENT SPECIES: MAIN CAUSES dog, dat and ru/horse/pig

A

1️⃣. Dogs - irreversible!
🔺Lymphocytic thyroiditis
🔺Thyroid atrophy (end stage problem)
🔺Hypophyseal disorders (secondary disorder! Uncommon).
2️⃣. Cats(dogs)
🔺Secondary to treatments for hyperthyroidism
3️⃣. Ruminants/ Horses/Pigs - reversible!
🔺Iodine deficiency
🔺Presence of dietary goitrogens (fodder plants)

(Goitrogens are substances which result in inadequate thyroid production and enlargement of the thyroid gland (goitre).)

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2
Q

Clinical signs accompanied by hypothyroidims:

A

1️⃣Lethargy and exercise intolerance
2️⃣Obesity (even though they dont eat much)
3️⃣Dermatological abnormalities: hair thinning on flanks and tail, poor quality coat, hyperpigmentation, pyoderma ➡️ itching

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3
Q

TESTS AVAILABLE for ca hypothyroidism

A

• Do them in this order! (If more are needed)
• Sample: serum! RIA is used, human kits must be validated for dogs!
1️⃣Total T4 (tT4)
2️⃣Endogenous TSH
3️⃣Free T4 (fT4) (not RIA, elisa and chemiluminesence)
4️⃣Stimulation tests
5️⃣Other laboratory tests:
tT4:TSH or fT4:TSH ratios have been reported to be useful in the diagnosis of hypothyroid dogs

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4
Q

TOTAL T4 (TT4) test

A

🔺TT4 is stable in serum and plasma.
🔺Canine basal T4 concentrations are around 4 times lower than in humans
🔺Measures protein-bound and free T4
🔺Human kits must be validated for dogs

🔺HIGH Sensitivity - Decreased in all dogs with hypothyroidism, 90% (10% has anti-thyroid ab which messes with result, so no tests will work, use thyroid supplementationinstead)
🔺LOW Specificity - A number of diseases cause low tT4 values, 25%

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5
Q

tT4 below reference range due causes:

A

1️⃣. Hypothyroidism
2️⃣. Non-thyroidal illness (NTI): e.g. hyperadrenocorticism(!! Fushings), diabetes mellitus, renal failure, hepatic disease
- In NTI reduced tT4 is a mechanism to decrease metabolic rate during chronic illness. It results from a reduction in TSH secretion, inhibition of the conversion of T4 to active T3 and decreased protein binding.)
3️⃣. Drugs e.g. glucocorticoids(!!), sulphonamides, anaesthetics(? Makes no sense), phenobarbital, Non-steroidal anti-inflammatories

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6
Q

Evaluation of ENDOGENOUS THYROID STIMULATING HORMONE (TSH) in canine

A

🔺TSH is stable in serum and plasma.
🔺Collect heparinized plasma or serum samples.
🔺Species-specific test required (human kits must be validated)
🔺RIA or chemiluminescence techniques are usually used

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7
Q

Canine TSH Increased and decreased:

A

TSH Increased:
1️⃣. Hypothyrodism (low-normal)
-Increased stimulation of the hypophysis (no neg feedback)
-Failure of negative feedback
2️⃣. Recovery from non-thyroidal illness (NTI)

TSH low ref range: (low-normal)
1️⃣. Hypothyroidism due to hypophyseal hypofunction (rare)
2️⃣ NTI

(Hypothyroidism is usually secondary to disease of the thyroid gland and therefore reduced T4 production, rarely secondary to reduced TSH production. In NTI cases TSH secretion is suppressed, as animal recovers there is a rebound increase in TSH production)

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8
Q

Why do we do Simultaneous measuerement of tT4 and TSH? Ca

A

Because we need both to make a conclusion:

Low tT4 + Increased TSH
➡️ Hypothyroidism

Low tT4 + Low ref range TSH
➡️ NTI, some drugs, Hypothyroidism due to hypophyseal disorders

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9
Q

Canine FREE T4 (FT4) evaluation

A

Find out if problem in brain or elswhere

🔺FT4 is stable in serum or plasma. -Heparinized plasma or serum samples.
🔺Equilibrium dialysis is BEST technique
🔺Similar to tT4 but:
• Less affected by NTI than tT4
• Decreased fT4 associated with anticonvulsant therapy

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10
Q

Decreased fT4 associated with anticonvulsant therapy in canine how

A

Dogs with low tT4 and low reference range TSH fT4 can help to differentiate the cause:
fT4 normal ➡️ NTI
fT4 decreased ➡️ Hypothyroidism due to hypophyseal disorders

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11
Q

canine THYROID STIMULATION(hypo) TESTS - how do we perform it, PROBLEMS

A

• TSH stimulation is considered the best test

  1. Collect serum sample for TT4
  2. Inject 0.1 IU/kg exogenous TSH (maximum 5 IU/dog) (Bovine TSH is commonly used, however
    recombinant TSH is now available)
  3. Collect Serum for TT4 after 6h

🔺The main problem is the lack of commercially available TSH.
🔺TRH stimulation is used when TSH is not available but results are less reliable.

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12
Q

canine THYROID STIMULATION TESTS - interpretation

A

🔺In Hypothyroidism there is a low basal T4 and minimal increase after TSH
🔺In NTI basal T4 is low and but increases by more than 1.5 times or is above given laboratory reference range after TSH
🔺In Normal dogs, basal T4 is within reference range and increases by at least 1.5 times after TSH

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13
Q

OTHER TESTS RESULTS THAT CAN INDICATE HYPOTHYROIDISM in ca

A

When we get eg fat dog in and tests say this, noe we can suspect hypothyroidism!

1️⃣Hypercholesterolaemia- 80% of hypothyroid dogs
🔺Thyroid hormone enhances cholesterol utilisation, reduces cholesterol synthesis and increases lipoprotein lipase activity. Hypothyroidism therefore cause an increase in blood cholesterol concentration.
2️⃣Anaemia - 50% of hypothyroid dogs (Non-regenerative)
🔺Thyroid hormone enhances the effect of erythropoietin on red cell production. Hypothyroidism therefore cause a mild non-regenerative anaemia.

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14
Q

HYPOTHYROIDISM IN Cats

A

We only look at Decreased tT4 in cat!

🔺Potential side-effect of treatment for hyperthyroidism -Lethargy, obesity and cutaneous changes
🔺 Low tT4 concentrations are associated with NTI in cats

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15
Q

HYPOTHYROIDISM IN RU

A

We usually only need to look at Decreased tT4 in Ruminants - fodder problem! Same in whole herd.
🔺Goitre, perinatal death
🔺Hypothyroidism has been associated with thyroid gland atrophy in dairy cows with fatty liver

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16
Q

HYPOTHYROIDISM IN EQ

A

Hypothyroidism has not been confirmed in adult horses.

(?)T3 reaction - has a stronger suppression effect on hypophysis than T4, check T4

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17
Q

HYPERTHYROIDISM IN DIFFERENT SPECIES: cats, dogs:

MAIN CAUSES

A
  1. Cats (COMMON)
    Thyroid neoplasia (usually benign)
  2. Dogs (RARE)
    Functional thyroid carcinoma

Overfeeding of raw body parts of neck with thyroid

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18
Q

Hyperthyroidims caused clinical signs in cats:

A 
1️⃣Weight loss 
2️⃣Polyphagia 
3️⃣Polydipsia, polyuria
4️⃣Hyperactivity
5️⃣Tachycardia
6️⃣Thyroid glands often palpable in the neck
19
Q

HYPERTHYROIDISM tests

A

1️⃣tT4 (99% only this needed inhyper) ⬇️ 1%
2️⃣T3 suppression test
3️⃣Other laboratory tests

Cats
1️⃣High tT4 = Hyperthyroidism
2️⃣tT4 within reference range can occur in hyperthyroid cats due to:
• Diurnal fluctuation
• NTI (causing lower tT4)
20
Q

T3 SUPPRESSION TEST

A

-Used to confirm hyperthyroidism in cats
➡️ usually when NTI downreg. + hyperthyroidism = normal/slightly high

  • Exogenous T3 is administered 8h for 3 days (suppress activity) time very important!
  • T4 is measured before & 4h after last administration

1️⃣Normal cat - T4 concentration decreases to < 50% at 4 hours
2️⃣Hyperthyroid cat - No variation in T4 concentration at 4 hours (tumors cant be suppressed)

21
Q

OTHER TESTS RESULTS THAT CAN INDICATE HYPERTHYROIDISM

A

(Indicate that there might be hyperthyroidism, do first)

1️⃣ Increased ALP (ALT, AST) in 2/3 of hyperthyroid cats
🔺 Increased ALP is due to increased production of the bone and liver isoenzymes, thought to be associated with increased basal metabolic rate.
3️⃣ Increased PCV
in 50% of hyperthyroid cats.
🔺Thyroid hormone enhances erythropoietin action and therefore PCV increases in hyperthyroidism

22
Q

TESTS OF ADRENOCORTICAL DISEASE

A

1️⃣Basal Cortisol (difficult stress during sampling and vet visit!)
2️⃣human assays for cortisol can be used in addisons not cushings! -Dynamic tests
• ACTH stimulation
• TRH Stimulation (in horses)
• Low dose dexamethasone suppression test (LDDS)
• High dose dexamethasone suppression test (HDDS)
3️⃣Urine cortisol:creatinine ratio
4️⃣Endogenous ACTH, eq mostly
5️⃣Other laboratory tests - basic labs

23
Q

HYPOADRENOCORTICISM types

A

1️⃣Primary hypoadrenocorticism (Addison’s disease)
• Deficient mineralocorticoid and glucocorticoid secretion due to adrenal disorders
• Well known but uncommon in the dog
• Rare in the cat
2️⃣Secondary hypoadrenocorticism
• ACTH deficiency due to pituitary disorders
• Occasionally reported in the dog

24
Q

Clinical Signs of HYPOADRENOCORTICISM

A 
Typically young!Signs of hypoadrenocorticism are mainly due to aldosterone deficiency which causes sodium and associated water losses: 
1️⃣Polyuria, 
2️⃣polydipsia 
3️⃣Vomiting, 
4️⃣diarrhoea 
5️⃣Muscle weakness, collapse 
6️⃣Bradycardia

(Decr na, incr K)

25
Q

ACTH STIMULATION TEST USED TO:

A
  • Confirm hypoadrenocorticism
  • Screen for hyperadrenocorticism (50% efficacy) not really used!
  • Monitor treatment of hyperadrenocorticism, (valid and important! Drugs will are dangerous, only this as monitoring is good
26
Q

ACTH STIMULATION TEST How to perform the test:

A

1️⃣Start at 8-9 AM with hospitalized patient
2️⃣Heparinised blood sample (0 hours)
3️⃣IV or IM tetracosactrin (synthetic ACTH)(0.25 mg for dogs > 5kg; 0.125 mg for cats and dogs <5kg)
4️⃣Dog: blood sample at 60 min
5️⃣Cat: blood samples at 30 & 60 min
6️⃣Measure plasma cortisol in all samples

This test detects: (LDDS better to find cushings! 95%)
🔺75% of Pituitary HAC dogs
🔺 50% of Adrenal HAC dogs

27
Q

ACTH STIMULATION TEST interpretation (graph)

A

🔺In Addison’s disease or iatrogenic hac there is a low basal cortisol and minimal increase after ACTH
In Normal dogs.
🔺Basal cortisol is relatively low and increases by 2-3 times after ACTH
🔺In Cushing’s disease basal cortisol is relatively high and increases by more than 2-3 times or is above the laboratory reference range after ACTH

28
Q

OTHER TESTS RESULTS THAT CAN INDICATE HYPOADRENOCORTICISM

A

1️⃣Anaemia
2️⃣ Lymphocyte count normal or increased in stressed animal
3️⃣ Na: K ratio below reference range (Na low, K increased)
4️⃣ Hypoglycaemia
5️⃣ Hypercalcaemia (mild)
6️⃣ Altered renal parameters (secondary)
7️⃣ Isosthenuria

29
Q

HYPERADRENOCORTICISM (HAC, Cushing’s syndrome) caused by,

A 
Glucocorticoid excess: common in dogs, rare in cats and horses.
Caused by:
1️⃣ Increased ACTH production from a Pituitary lesion, (pituitary dependent hyperadrenocorticism) 
🔺 85% of dogs 
🔺 100% of horses
2️⃣Adrenocortical tumour
(adrenal dependent hyperadrenocorticism)
🔺 15% of dogs
30
Q

HYPERADRENOCORTICISM (HAC, Cushing’s syndrome clinical signs

A 
1️⃣Polyphagia (pot belly)
2️⃣weight gain 
3️⃣Polyuria, polydipsia
4️⃣Alopecia and other skin changes, eq gets more hair!
5️⃣Lethargy, panting
31
Q

LOW DOSE DEXAMETHASONE SUPPRESSION TEST (LDDS) USED TO:

A

ONLY DOGS!
🔺Screen for hyperadrenocorticism (HAC): Low dose of dexamethasone will suppress normal pituitary gland but not in HAC Sensitive test (detects 􏰆95% of hyperadrenocorticism dogs = best! Why do anything else??)

Cats dont work with such low dose

32
Q

LOW DOSE DEXAMETHASONE SUPPRESSION TEST (LDDS) How to perform the test

A

1️⃣Start at 8-9 AM with hospitalized patient 2️⃣Heparin sample (basal)
3️⃣IV dexamethasone (0.01 mg/kg BW)
4️⃣Dog: blood samples at 4 and 8 h after dex.
5️⃣Measure plasma cortisol in each of the samples

  • The results of a LDDS may (30-40%) help to differentiate pituitary HAC and adrenal HAC:
    Adrenal is more stubbern and will not be suppressed from basal, while In cases of pituitary hyperadrenocorticism plasma cortisol is decreased at 4h (<50% baseline) but is similar to basal concentration at 8h

Normal: quick suppression and stays!

33
Q

HIGH DOSE DEXAMETHASONE SUPPRESION TEST (HDDS)

A

1️⃣ DOG - differentiation, we only do when we know cushings is present!Used after the diagnosis of hyperadrenocorticism to differentiate the cause:
pituitary dependent or adrenal tumors 2️⃣CAT - diagnosis, confirm hyperadrenocorticism
🔺The HDDS test is performed in the same way as the LDDS, however the dose of dexamethasone is increased (0.1 mg/kg body weight)
🔺In cats blood for cortisol concentration is taken at 4, 6 and 8h.

Adrenal is stubberns and wont be suppressed for long, while pituitary will be suppressed (at 4h)

34
Q

FELINE HDDS INTERPRETATION

A

🔺Used in the diagnosis of hyperdarenocorticism.
🔺HDDS results can vary in feline Cushing’s disease(rare)
🔺Absence of cortisol suppression at 4 or 8 hours or both confirms the diagnosis. (Anything other than normal is cushings min 8h)

35
Q

URINE CORTISOL-CREATININE RATIO

A

🔺Screening test for hyperadrenocorticism,
🔺Collect urine at home without stress (good! Cortisol!)
🔺Measure urine cortisol & urine creatinine
Interpretation
🔺Normal ratio excludes hyperadrenocorticism
🔺Increased ratio in:
• suspicion for cushing, dog: LDDS, cat: HDDS

Cortisol is excreted in the urine and its urine concentration appears to correlate with plasma concentration.
Comparing the concentration to creatinine compensates for dilution or concentration of the urine in the distal nephron.

36
Q

ENDOGENOUS ACTH DETERMINATION

A

Used to differentiate PDH and ADH, its an unstabile hormone, bad in dog/cat, ok in eq

🔺Fragile hormone:
needs special sample handling (contact laboratory before sampling) 🔺Episodic secretion
🔺Overlapping values

37
Q

OTHER TESTS RESULTS THAT CAN INDICATE HYPERADRENOCORTICISM

A 
"Steroid effect":
– Erythrocytosis
– Stress leukogram
– Increased ALP (steroid isoenzyme)
– Hypercholesterolaemia
– Mild hyperglycaemia
– Reduced urine SG, occasionally glucosuria
38
Q

TESTS FOR EQUINE HYPERADRENOCORTICISM

A

1️⃣TRH!! Stimulation test
Incr of >30-70% above basal = cushings

(2️⃣ Dexamethasone suppression test
3️⃣ ACTH stimulation test)

39
Q

TRH Stimulation test in eq

A

🔺Post TRH cortisol increase of >30-70% above basal = Hyperadrenocorticism
🔺Although, the precise mechanism of action is not well known, TRH affects the brainstem in horses with hyperadrenocorticism producing an increase in cortisol levels in these cases.
How to perform TRH stimulation test:
1️⃣ Collect serum for cortisol (0 minutes)
2️⃣ Inject 1 mg TRH IV
3️⃣ Collect serum for cortisol at 15, 30 and 60 minutes

40
Q

PARATHYROID HORMONE

A

🔺Require EDTA blood separated and frozen immediately
🔺Elevated PTH may be:
1️⃣Primary (gland hyperplasia or neoplasia)
2️⃣Secondary to:
-Renal disease
-Calcium deficient diet

🔺Reduced PTH usually due to inadvertant removal of the parathyroid gland or parathyroiditis
🔺Some paraneoplastic diseases produce a PTH-like hormone called PTH-related peptide (PTH-rp) that can be also measured

41
Q

INSULIN

A

🔺Serum sample required
🔺Need to measure insulin concentration in conjunction with glucose
🔺Can use a glucose: insulin ratio to help diagnose insulinoma.
- However amended glucose: insulin ratio (AGIR) has fallen out of favour
🔺Insulin assay must be validated for the species.
- Usually human inmunoassays are valid for dogs but not always for cats.
- Amended Glucose : Insulin ratio (based on human studies) NOTE: this ratio uses non-SI Units Insulinoma suspected when AGIR = >30

42
Q

GROWTH HORMONE

A

This is not routine examination and a few laboratories are measuring it for scientific purposes.

43
Q

PROGESTERONE

A
  • Serum sample required
  • Milk concentration used for diagnosis of pregnancy in the cow.
  • Not useful in the bitch (concentrations remain stable).
44
Q

Relaxin

A
  • Synthesised by the corpus luteum and placenta.
  • In some species e.g.dogs, plasma concentration increases during pregnancy.
  • Patient-side test available

Lab Diagnostics (16 decks)

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