reference ranges

Question 1

what are the purposes of lab rest requests?

Answer 1

• screen for disease
• risk stratification
• diagnosis of disease
• prognosis
• monitoring progression/remission of a disease
• monitoring therapy

Question 2

what types of samples are analysed in clinical chemistry?

Answer 2

• serum
• whole blood
• urine
• faeces
• sweat
• cerebrospinal fluid
• renal stones
• post-mortem samples
• miscellaneous fluids

Question 3

what can be measured in clinical chemistry?

Answer 3

• ions (sodium, potassium…)
• metabolites (glucose, lactate…)
• waste/breakdown products (urea, creatinine…)
• markers of cell damage (enzymes, trop T)
• enzymes
• plasma proteins (albumin, immunoglobulins…)
• antibodies
• hormones
• drugs
• vitamins
• metals

Question 4

what are the 5 different testing groups?

Answer 4

• renal function
• liver function
• bone profile
• thyroid function
• lipid profile

Question 5

what do you test for with renal function?

Answer 5

sodium, potassium, urea & creatinine

Question 6

what do you test for with liver function?

Answer 6

total protein, albumin, bilirubin, alkaline phosphatase, alanine transaminase

Question 7

what do you test for with bone profile?

Answer 7

total protein, albumin, calcium, phosphate, alkaline phosphatase

Question 8

what do you test for with thyroid function?

Answer 8

TSH (free T4, free T3)

Question 9

what do you test for with lipid profile?

Answer 9

total cholesterol, HDL-cholesterol, non-HDL cholesterol, triglycerides

Question 10

how do you generate a reference range?

Answer 10

• take a large number of healthy individuals
• measure the substance of interest
• calculate the mean and standard deviation of the results
• the reference range is: mean -2SD to mean +2SD

Question 11

what percentage of the population are within the reference range?

Answer 11

95%

Question 12

what percentage of the population are lower than the reference range?

Answer 12

2.5%

Question 13

what percentage of the population are higher than the reference range?

Answer 13

2.5%

Question 14

generally how are reference ranges interpreted?

Answer 14

• results outside the reference range do not necessarily imply disease
• they may be a change finding in a healthy individual
• the more extreme the value the more likely that an abnormality/disease is present
• results inside the reference range to not necessarily exclude disease

Question 15

why do creatinine levels vary with sex and age?

Answer 15

it is produced by muscle so generally, men have more muscle than women and muscle mass increases with age

Question 16

what sources does alkaline phosphatase have?

Answer 16

• liver
• bone
• intestine
• kidney
• placenta

Question 17

when you get the reference ranges what are the questions you need to be asking?

Answer 17

• what was the reason for requesting the tests?
• what stands out - high, low?
• what do the patterns of results tell you?
• does the clinical information change your thinking?
• do previous results or does the history add insight?
• do you need further information or would more tests be helpful?