Clinical Biochemistry

Question 1

Why would one request a biochemical test?

Answer 1

• To confirm a diagnosis or to differentiate between diagnosis’.
• To monitor the progress of a condition.
• For prognosis.
• To screen for conditions.

Question 2

Outline the clinical biochemistry cycle.

Answer 2

1. Clinical question (e.g. glucose or insulin levels in diabetes).
2. Request form.
3. Take sample.
4. Transport to lab.
5. Reception at lab.
6. Analysis.
7. Report.
8. Question answered.

Question 3

What steps must be followed when completing a biochemical test request form?

Answer 3

Must be as complete as possible.
Must contain the patients ID.
Indicate the tests required.
Indicate the diagnosis suspected/clinical symptoms.
List current drug therapies.

Question 4

What steps should be taken when taking a sample for a biochemical test?

Answer 4

Must be taken in an appropriate test tube.
Good sampling technique is essential.
Appropriate storage is essential to ensure the sample is valid.

Question 5

How is the use of near patient testing changing in modern medical settings?

Answer 5

Near patient testing is becoming more prevalent in medical settings, especially in primary healthcare where the medical team may not have access to complex laboratories or where the results of a test are needed quickly.

Question 6

What is near patient testing?

Answer 6

Biochemical testing at the patients bedside, providing quick results.

Question 7

What are some negative aspects of near patient testing?

Answer 7

Costs being invariably higher than traditional lab tests and the maintenance and calibration of instruments.

Question 8

How should biochemical test results be interpreted?

Answer 8

Test results should always be interpreted in terms of the given reference range for the specific biochemical entity being tested for.

Question 9

Where are the reference ranges for biochemical tests derived from?

Answer 9

These reference ranges are derived from population studies of healthy individuals and represent the data given by 95% of the normal distribution.

Question 10

What factors can affect biochemical test results?

Answer 10

Biological variation, analytical variation, drugs, disease process.

Question 11

What biological factors can affect biochemical test results?

Answer 11

o	Gender.
o	Age.
o	Race.
o	Diet.
o	Time of day.
o	Posture.
o	Exercise.
o	Menstrual cycle.
o	Pregnancy.

Question 12

How can analytical variation affect biochemical test results?

Answer 12

o Very small variations on repeated testing.

o Quality control essential within labs/between labs.

Question 13

What are the percentages of solids and fluids in men?

Answer 13

40% solids and 60% fluids.

Question 14

What are the percentages of solids and fluids in women?

Answer 14

45% solids and 55% fluids.

Question 15

What proportion of a persons fluids is composed of intracellular fluids?

Answer 15

2/3.

Question 16

What proportion of a persons fluids is composed of extracellular fluids?

Answer 16

1/3.

Question 17

Why do the elderly generally have less water?

Answer 17

A lower amount of muscle mass.

Question 18

Do children have a higher or lower proportion of fluids compared to adults?

Answer 18

Higher.

Question 19

How much water should a typical 70kg adult to drink per day?

Answer 19

2.5-3.0 L.

Question 20

Where does one usually get water from?

Answer 20

We get water from the food we eat, fluids we drink, and occasionally via artificial sources such as IV lines.

Question 21

Through what means is water lost?

Answer 21

• Urine.
• Faeces.
• Breathing.
• Body surface via transpiration.
• Evaporation from burns.
• Blood loss.

Question 22

What is the skin turgor test?

Answer 22

This is a quick and easy test to see if a patient is possibly dehydrated. It is performed by pinching the skin on the back of the hand.

Question 23

In a skin turgor test, how should a non-dehydrated person’s skin react?

Answer 23

In a non-dehydrated person, the skin should spring back into place almost instantly.

Question 24

In a skin turgor test, how should a dehydrated person’s skin react?

Answer 24

If the person is dehydrated, the skin may take several seconds to go back to place.

Question 25

Why doesn’t the skin turgor test work particularly well in the elderly?

Answer 25

This doesn’t work particularly well in the elderly as their skin lacks some of the elasticity that a younger patients skin has.

Question 26

What are the fluid statuses a patient may be categorised into?

Answer 26

Hypovolemic, evolemic, hypervolemic.

Question 27

Define hypovolemia.

Answer 27

Not enough extracellular fluid, there may be sodium deficit but a smaller H2O deficit. There may be excessive loss of one or more body fluids.

Question 28

What may cause hypovolemia?

Answer 28

 Adrenocortical failure.
 Poorly controlled IBD/crones.
 Severe vomiting, diarrhoea, sweating, burns.

Question 29

How may hypovolemia be treated?

Answer 29

Remove identifiable underlying causes. Correct hypovolemia with IV isotonic saline (0.9%) until BP is restored.

Question 30

Define evolemia.

Answer 30

Water alone is retained. Often due to abnormally high water intake i.e. through IV drip.

Question 31

What can cause evolemia?

Answer 31

	SIADH – incorrect water retention – can be caused by a tumour.
	Hypothyroidism – poorly controlled.
	Glucocorticoid deficiency.
	Trauma (acute).
	Surgery (acute).
	Pain, stress.
	Can be drug induced:
•	SSRIs.
•	Potassium sparing diuretics.
•	NSAIDs.

Question 32

Outline the management of evolemia.

Answer 32

 Restrict fluids (800ml – 1.5L per day).
 Measure serum osmolality – knowing this is essential.
 For SIADH, fluid restrict, then administer demeclocycline (blocks ADH).
• Then tolvaptan – a vasopressin receptor antagonist
 Lithium can be used however this is unlicensed.
 Always treat the cause, however sometimes, other treatments are needed.

Question 33

Define hypervolemia.

Answer 33

Excess of extracellular fluid. More water retained than sodium.

Question 34

What are the likely causes of hypervolemia?

Answer 34

 Congestive cardiac failure.
 Liver cirrhosis.
 Nephrotic syndrome.
 Renal failure.

Question 35

What are the symptoms of hypervolemia?

Answer 35

 Peripheral oedema.
 Ascites.
 Elevated JVP.
 Fluid in the lungs in extreme cases.

Question 36

Outline the treatment of hypervolemia?

Answer 36

 Deal with the underlaying cause.
 Reduce total body water with a combination of fluid restriction (1-1.5L a day) and loop diuretics.
 If refractory, vasopressin (ADH) receptor antagonist, e.g. Tolvaptan.