Basic clinical biochemistry

Question 1

What are test results useful for?

Answer 1

Detecting health problems and diagnosing. Screening for latent infection (hidden or dormant). Determining prognosis and guiding treatment.

Question 1

What is clinical biochemistry?

Answer 1

The division of medical lab that deals with the measurement of biochemicals in blood, urine and other bodily fluids.

Question 2

What are examples of samples?

Answer 2

Blood, urine, cerebrospinal fluid, synovial fluid, gastric fluid, duodenal fluid, tears saliva, biopsy material.

Question 3

What is precision?

Answer 3

Repeated measurements of analyte in the sample should give similar results.

Question 4

What is accuracy?

Answer 4

Test results should reflect true value.

Question 5

What are the requirements for a test?

Answer 5

Sensitive- limit of detection of analyte must be appropriate. Specific- Must be able to distinguish analyte from other molecules.

Question 6

What are reference ranges?

Answer 6

To be clinically useful we need to know if a test result is abnormal. Compare test value with reference range.

Question 7

How is the reference range constructed?

Answer 7

95% of normal values lie within it. 1 in 20 chance that a normal test result will be outside the range. For a normal distribution reference= mean +/- 2 SD.

Question 8

What is the cut off value?

Answer 8

Value for assigning to positive for disease group set to minimise false negatives and false positive being assigned.

Question 9

What is clinical sensitivity?

Answer 9

The proportion of positives tests from disease group. Sensitivity %= TP/(TP+FN)X100

Question 10

What is clinical specificity?

Answer 10

The proportion of negative results from the healthy group. Specificity %= TN/(TN+FP) X100

Question 11

How do you calculate PPV?

Answer 11

True positive/true positive + false positive

Question 12

How do you calculate NPV?

Answer 12

True negative/true negative + false negative

Question 13

What is an example of using enzyme levels in diagnosis?

Answer 13

Tissue damage releases enzymes which enter the plasma. Cytosolic enzymes released readily following loss of cell membrane integrity. Membrane bound enzymes released on more extensive cell damage/death. Increased plasma enzyme activity indicates tissue damage.

Question 14

How do isoenzymes show tissue damaging?

Answer 14

The pattern of isoenzymes in the plasma may reflect where tissue damage has occurred.

Question 15

What are isoenzymes?

Answer 15

Different enzymes coded by different genes acting on the same substrate are isoenzymes.

Question 16

What are some examples of isoenzymes?

Answer 16

Aminotransferases, creatine kinase, LDH, alkaline phosphatase, amylase.

Question 17

How are isoforms of LDH used in clinical testing?

Answer 17

Apply blood sample and run electrophoresis, find different sizes from different isoforms.

Question 18

What does alkaline phosphatase show in clinical testing?

Answer 18

High levels in liver and bone also in placenta and intestine. Total activity used as an indicator for bone or liver disease. Elevated levels indicate cholestatic liver disease.

Question 19

What does acid phosphatases show in clinical testing?

Answer 19

Removal of phosphate groups from a range of substrates. High levels in prostate gland. Elevated indicates cancer.

Question 20

What does glutamyltransferase indicate show in clinical testing?

Answer 20

Levels mirror alkaline phopshatases. Highest levels in cholestasis.

Question 21

What does amylase show in clinical testing?

Answer 21

Elevated levels may indicate acute pancreatitis. Used to differentiate from appendicitis in patients with acute abdnominal pain.

Question 22

What is the liver function tests?

Answer 22

AST and ALT high levels in hepatitis, heptacellular toxicity. GGT raised in alcohol abuse (cirrhosis).

Question 23

What does high levels of creatine kinase indicate?

Answer 23

Muscle damage.

Question 24

What order rate do enzymes have in assays?

Answer 24

Zero order (NOT limited by substrate concentration). Time period must be chosen so substrate does NOT fall below a saturating concentration as it is consumed.

Question 25

What is an example of a coupled assay?

Answer 25

Creatine phosphate assays. Many assays coupled to NADH or NADPH production.

Question 26

What do plasma proteins tell us?

Answer 26

Levels of proteins normally found in plasma indicate disease. Lowered total plasma protein may indicate liver damage, kidney disease, malnutrition. Raised total plasma protein may indicate dehydration, large increase in level of an individual protein.

Question 27

Look at graphs interpreting serum protein electrophoresis patterns.

Answer 27

Look at graphs interpreting serum protein electrophoresis patterns.