Chemical Pathology

Question 1

Three main causes of hypernatraemia

Answer 1

1 hypovalaemia - GI loss/diuretics

2 euvolaemia - respiratory losses

3 hypervolaemia - mineralocorticoid excess

Question 2

Urine concentrates after 8h deprivation test indicates

Answer 2

Primary polydipsia

Question 3

Urine doesn’t concentrate over 8h deprivation test but does with the administration of desmopressin

Answer 3

Cranial diabetes insipidus

Question 4

Urine fails to concentrate after 8hour deprivation test and desmopressin administration

Answer 4

Nephrogenic diabetes insipidus

Question 5

Causes of nephrogenic diabetes insipidus

Answer 5

ADH insensitivity due to - lithium/inherited/chronic renal failure

Question 6

What is hypokalaemia and what are four causes?

Answer 6

<3.5mmol/l

1 GI loss

2 redistributative - insulin

3 renal loss - excess cortisol/osmotic diuresis

4 rarely - tubular acidosis/hypomagnesia

Question 7

Where is potassium normally predominately found

Answer 7

Intracellularly

Question 8

What is hyperkalaemia and what are three causes?

Answer 8

> 5.5mmol/l

1 excessive intake

2 movement out of cells - acidosis/decreased insulin/catabolic state

3 decreased excretion - acute renal failure/CRF/Addisons/NSAIDs/ACEi/spironolactone

Question 9

What are five causes of decreased K excretion which lead to hyperkalaemia?

Answer 9

ACEi
Spironolactone
Acute renal failure
Chronic renal failure
NSAIDs
Addisons

Question 10

What is the rule linking pH to serum potassium?

Answer 10

For every 0.1 decrease in pH there is a 0.7 increase in K

Question 11

Normal range for pH

Answer 11

7.35-7.45

Question 12

Normal range for Co2

Answer 12

4.7-6

Question 13

Normal range for bicarbonate

Answer 13

22-30

Question 14

Normal range for O2

Answer 14

10-13

Question 15

What are the steps you follow when looking at a blood gas (4)

Answer 15

1 pH
2 Does the CO2 fit with the pH
3 Does the bicarbonate fit with the pH
4 Any compensation>

Question 16

How is the anion gap calculated and what is it normally?

Answer 16

(Na+k)-(Cl+Hco3)

Usually 14-18

Question 17

Name four causes of a raised anion gap

Answer 17

1 ketoacidosis
2 uraemia
3 lactic acidosis
4 toxins

Question 18

What causes the osmolar gap to be raised above 10?

Answer 18

An abnormal solute - ethylene glycol/ethanol/methanol/mannitol

Question 19

Name the three measures of liver synthetic function

Answer 19

Glucose
INR
Albumin

Question 20

Name the three causes of a raised alkaline phosphatase

Answer 20

Cholestasis
Pregnancy
Bone disease

Question 21

What does a raised AST and ALT mean?

Answer 21

Hepatocyte death ie viral/alcohol

Question 22

What does a raised gamma GT mean?

Answer 22

Chronic alcohol use, bile duct disease and metastases

Used to confirm hepatic source of raised ALP

Question 23

Inheritance of acute intermittent porphyria

Answer 23

Autosomal dominant

Question 24

What enzyme is deficient in acute intermittent porphyria

Answer 24

HMB synthase deficiency

Question 25

Fifth year medical student with abdominal pain, nausea and vomiting and muscle weakness. Their urine is noticed to be a port wine urine.

Answer 25

Acute intermittent porphyria

Question 26

What are some of the precipitating factors for acute intermittent porphyria

Answer 26

ALA synthase inducers - steroids/ethanol/barbiturates Stress Decreased caloric intake

Question 27

What type of symptoms does acute intermittent porphyria cause

Answer 27

Neuro-visceral

Question 28

Photosensitivity and burning itching oedema after sun exposure

Answer 28

Erythropoietin protoporphyria

Question 29

Enzyme deficiency in porphyria cutanea tarda

Answer 29

Uroporphyrinogen decarboxylase deficiency

Question 30

Vesicles and superficial scars from them on sun exposed sites

Answer 30

Porphyria cutanea tarda

Question 31

Increased urinary uroporphyrins, coproporphyrins and ferritin

Answer 31

Porphyria cutanea tarda

Question 32

Patient with light sensitivity and red urine

Answer 32

Congenital erythropoietic porphyria

Question 33

What is the aim of the combined pituitary function test, contra-indications and side effects

Answer 33

Used to assess all components of the anterior pituitary Avoid in ischaemic heart disease/epilepsy/untreated hypothyroid Side effects - sweating, palpitations, LOC. transient metallic taste with the injection of TRH

Question 34

What does the combined pituitary function test consist of?

Answer 34

Insulin tolerance test - cortisol and GH Thyroptrophin Releasing Hormone test - TSH Conadotrophin releasing hormone test - LH and FSH

Question 35

What is the expected response to an insulin tolerance test

Answer 35

Cortisol increase from >170 to >500 | GH increase >6mcg/l

Question 36

What is the expected response to the thyrotrophin releasing hormone test?

Answer 36

TSH increase >5 and the 30 minutes value greater than the 60 minute value.

Question 37

What does a 60min value of TSH greater than the 30min value in the TRH test mean?

Answer 37

Primary hypothalamic disease

Question 38

What does an exaggerated response to the TRH test mean?

Answer 38

Hypothyroid

Question 39

What is a normal response to the GRH test?

Answer 39

Peak at 30 or 60 mins | LH >10 and FSH >2