Interpreting Test Results

Question 1

What is chemical pathology?

Answer 1

involves the biochemical investigation of bodily fluids such as blood, urine and cerebrospinal fluid

Question 2

Core clinical process?

Answer 2

History/exam –> lab request –> lab report –> consultation

Question 3

Contents of lab reports?

Answer 3

Demographic details - from request

Results - from laboratory analysis

Reference ranges - from scientific knowledge

Comments & Advice - from experience

Question 4

What is ‘The Normal Range’?

What term should be used instead?

Answer 4

Defines the values of a biochemical test found in healthy subjects against which patient values can be compared.

Preferred term is ‘Reference Range’

Question 5

What is the ‘ideal diagnostic test’?

Answer 5

Has the potential to completely discriminate subjects with and without disease (never find this in practice - have false negatives and positives)

Question 6

To improve tests, a more appropriate ‘normal’ population should be selected.

Here are some examples of ‘normal’ population

Answer 6

Patients with similar presenting symptoms
e.g. chest pain
Same age
Same gender
Hospitalised ‘normals’
Same underlying disease

Question 7

What are some factors that affect reference ranges?

Answer 7

Age
Gender
Diet
Pregnancy
Time of month
Time of day (cortisol) 
Time of year
Weight
Stimulus

These need to be borne in mindwhen interpreting results

Question 8

How do cortisol levels change throughout the day?

Answer 8

Normally, cortisol levels rise during the early morning hours and are highest about 7 a.m. They drop very low in the evening and during the early phase of sleep.

Question 9

When are cortisol tests usually done?

Answer 9

Around 9am or midnight

Random cortisol tests aren’t as reliable as reference range widens

Question 10

Case 1: Initial

16 year old boy presents to hospital in deep coma.

On examination he is severely dehydrated and has deep sighing respiration.

1. What are the two most likely diagnoses?
2. What extra information would you like to obtain?
3. What tests are needed and why?
4. What test(s) would you wish to use to follow-up the patient?

Answer 10

1. Diabetes, Salicylate OD (aspirin)
2. Previous history - weight loss, polyuria etc
3. Glucose, gases, U&E, salicylate
4. HbA1c

Question 11

What is Kussmaul breathing in response to?

Answer 11

A type of hyperventilation that is the lung’s emergency response to acidosis.

Question 12

What characterises Kussmaul breathing?

Answer 12

Kussmaul breathing causes a laboured, deeper breathing rate.

Question 13

In what conditions is Kussmaul breathing seen in?

Answer 13

Conditions that cause metabolic acidosis, particularly diabetes (diabetic ketoacidosis)

Question 14

What does an HbA1c test show you?

Answer 14

An HbA1c blood test can give an indication of whether blood glucose levels have been higher than normal over the last few months, by looking at how much sugar (glucose) is bound in your red blood cells

Question 15

Case 1: further info

Previous history reveals severe weight loss, thirst and polyuria over the previous 4 weeks.

In the last few days he has found it painful to pass his urine and has had several bouts of violent shivering.

Found to have high glucose, low pH, increased [H+] (massively acidotic), low Na, high K, high urine ketones

1. What could violent shivering be due to?
2. What could painful urine be due to?
3. What is diabetes?
4. What is appropriate treatment?

Answer 15

1. Rigors (seen in severe infection)
2. Infection
3. Diabetic ketoacidosis
4. Give him insulin to lower glucose and stop fat breakdown (ketones will disappear)

Question 16

What causes urine ketones in diabetic ketoacidosis?

Answer 16

Lack of insulin causes fat to break down which goes to the liver to become metabolised to make ketones

Ketones are highly acidotic

Question 17

Normal interaction of cortisol and insulin?

Answer 17

Cortisol makes fat and muscle cells resistant to the action of insulin, and enhances the production of glucose by the liver. Under normal circumstances, cortisol counterbalances the action of insulin.

Question 18

Why should potassium be monitored during treatment of DKA?

Answer 18

After insulin treatment is initiated, potassium shifts intracellularly and serum levels decline. Replacement of potassium in intravenous fluids is the standard of care in treatment of DKA to prevent the potential consequences of hypokalemia

Question 19

Consequences of hypokalaemia?

Answer 19

cardiac arrhythmias and respiratory failure