The important of reference ranges and sources of variation

Question 1

What happens if the diagnostic cut off value for a test is set too high?

Answer 1

There will be no false positives, but there will be an increase in the number of false negatives.
specificity increases but sensitivity decreases.

Question 2

What happens if the diagnostic cut off value for a test is set too low?

Answer 2

There will be no false negatives, but an increase in the number of false positives. Sensitivity increases but specificity decreases.

Question 3

Define sensitivity

Answer 3

The percentage of people correctly identified to have the disease

Question 4

Define specificity

Answer 4

The percentage of people correctly identified to not have the disease

Question 5

Why do sample collection tubes come in different colours?

Answer 5

To represent different preservatives or anticoagulants, used for different tests e.g.
grey lid - fluoride oxalate
yellow lid - clot activator

Question 6

Give some examples of intervidual variation

Answer 6

Age: plasma, urate and cholesterol levels vary between ages
Gender: differnces in conc between the sexes. Obvious - plasma, sex hormones but also iron, urate and urea.
Ethnicity: plasma conc and protein conc although this is difficult to distinguish from the effects of culturual/dietary factors.

Question 7

Give some examples of intravidual variation

Answer 7

Menstraul cycle - variance from cycle to cycle, including iron conc
Posture: proteins show sig differences between blood taken from ambulant (walking) and supine (lying down) individals

Question 8

Why do we biochemically test?

Answer 8

• Diagnosis (confirm or reject clinical diagnosis)
• Monitoring (natural progression of disease or the response to treatment)
• Prognosis (information regarding the outcome of the disease)