Lecture 1: Introduction to Module

Question 1

What is clinical biochemistry?

Answer 1

Diagnosis and management of disease through analysis of blood, urine and other bodily fluids.

Question 2

What are clinical biochemistry tests used for?

Answer 2

Help make a diagnosis, or to confirm one. To screen for latent disease. Help evaluate a diseases progression, or to help monitor the progress of a disease.

Question 3

Name the samples measured in clinical biochemistry.

Answer 3

Blood, plasma and serum
Urine
Cerebrospinal fluid
Synovial fluid
Gastric fluid
Duodenal fluid
Tears
Saliva

Question 4

What is the difference between plasma and serum?
Which is used mainly in biochemistry?

Answer 4

Serum is plasma without any clotting factors.
Serum is preferred in biochemistry.

Question 5

Where can lab tests be performed?

Answer 5

Clinical laboratory in a hospital.
Specialist reference laboratory
Point of care (POC)
Home testing

Question 6

What is a diagnosis?

Answer 6

Determining the pathology with an individual. This is based off their medical history, clinical signs on examination, putting together a list of differential diagnoses and investigating to refute or confirm certain diagnoses.

Question 7

What is a prognosis?

Answer 7

The prediction or probable cause of disease. Similar range of test as used for diagnosis. The tests will help predict the course of the disease.

Question 8

What is measured after treatment with a drug has started?

Answer 8

Tests can be used to detect damage to organs from treatment, e.g. electrolyte imbalance in renal treatment.

Testing for a drug’s toxicity is also possible.

Question 9

Give an example of a disease in which can be mass screened. Explain this disease.

Answer 9

PKU or phenylketonuria. It involves the build up of phenylalanine in the blood, due to a defective phenylalanine hydroxylase enzyme.
Phenylalanine hydroxylase normally adds a hydroxyl group to phenylalanine to produce tyrosine, which is hugely important in the production of catecholamines. melanin and proteins.

Question 10

What is screening?
(Give one example of mass screening)

Answer 10

Detection of sub-clinical diseases before symptoms present themselves.
Sometimes the cost of screening is not worth the benefit.

Question 11

What is Inter-Individual biological variation? (Pre-analytical Variation)

Answer 11

Everyone has slightly different biochemical profiles, and therefore tests will never give identical results even in healthy individuals. Factors such as age, gender, race, and other genetic differences.

Question 12

What is intra-individual biological variation? (Pre-analytical Variation)

Answer 12

Variation that occurs due to biochemical variations that are present from day to day. This can include hormonal changes due to stress, or time of day, or hormonal cycles (especially in women), as well as exercise.

Question 13

What non-biological factors can affect test results? (Pre-analytical Variation)

Answer 13

If the specimen is collected from different areas of the body (blood from artery will have different chemical balances to capillary or venous). Urine content can vary greatly.

Handling of specimens can vary due to errors in storage (not incubated, or put in fridge) and labelling.
Insufficient centrifugation or over centrifugation can cause error.

Question 14

Most analyses are performed on either serum or plasma, how can you obtain these specimens?

Answer 14

Serum is obtained by centrifugation before allowing the sample to clot. Plasma samples are obtained by adding an anticoagulant after centrifugation.

Question 15

What is the order or specimen collection (Tubes and order of draw).

Answer 15

Blood culture (contains culture medium for pathogens) [colour varies]

Coagulation studies (sodium citrate, weak anticoagulant) [light-blue]

Serum tube (Clot activator due to silicon coating, but no additives or gel, used if test might be affected by gel) - chemistry [red]

Serum Separator Tube, or SST (Clot activator silicon, thixotropic gel that is less dense than cells, will separate serum) - chemistry [gold]

Plasma Separating Tube, or PST (heparin, which is an anticoagulant, inhibits thrombin, stopping fibrinogen turning to fibrin) - chemistry [light-green]

Haematology/Haemoglobin A1C (K2 EDTA, a strong anticoagulant and chelating agent) [purple]

Blood group cross-matching (Also contains EDTA, but used more for transfusion labs) [light-pink]

Glucose test (potassium oxalate, anticoagulant that works well with antiglycolytic sodium fluoride) [grey]

Question 16

What is the order of vacutainers used in blood tests (order of draw)?

Answer 16

Boys - Blood culture
Love - Light blue
Ravishing - Red
Girls - Gold
Like - Light-green
Putin - Purple
Loves - Light-pink
Genocide - Grey

Question 17

What is a random urine sample used for?

Answer 17

This is for qualitative analysis, showing if a particular substance is present or not (e.g. dipstick test).

Question 18

What is a 24 hour collection of urine used for?
How is it performed?

Answer 18

It is used for quantitative analysis of a sample, telling how much of a certain substance is present in urine.
Used for protein excretion, electrolytes, creatinine, etc.
This eliminates diurnal variation.

Test is performed after urinating for the first time in the morning, and after noting the time, collecting every drop of urine for a 24hr period.

Question 19

How can urine tests help determine kidney damage?

Answer 19

Albumin : Creatinine ratio is used to determine how much albumin is ‘leaking’ into the urine from damaged nephrons. Creatinine is used to correct for hydration.

Question 20

How much urine samples be prepared are why?

Answer 20

Urine preservatives are added to reduce bacterial growth, chemical decomposition or prevent precipitation of certain components.

Question 21

What problems can occur in specimen collection?

Answer 21

Poor blood collection practice, too violent with sample, resulting in haemolysis, and releasing electrolytes and other red cell constituents.

Stasis during venipuncture, tourniquet use can elevate concentration of constituents as water diffuses into interstitial space.

Taking blood sample from location of IV drip will dilute sample.

Incorrect timing can occur in 24hr urine tests + other time dependent tests.

Incorrect specimen containers.

Insufficient sample size.

Incorrect storage, too hot, too cold, etc.

Question 22

What is analytical variation?

Answer 22

The accuracy of the results that are obtained from a sample.

Question 23

What can influence analytical variation?

Answer 23

Changes that have occured after the sample can left the patient, such as haemolysis. Certain tests may be influenced by factors such as lipaemia and hyperproteinuria.

The assays performed can vary in accuracy, precision, sensitivity and specificity.

Question 24

What is the precision of an assay?What equation is used to measure the imprecision of a test?

Answer 24

The precision is how close repeated measurements are to one another.

%CV is used to measure imprecision.

CV (%) = SD of repeated measurements x 100 / Mean of repeated measurements.

Question 25

What is the difference between accuracy and precision in an assay?

Answer 25

Accuracy signifies how close a measurement is to its true value, whereas precision is how similar each repeat is.

Question 26

What will results obtained from test be compared against?

Answer 26

Reference Ranges - A ‘normal’ range that is calculated from a sufficient reference population.

Question 27

What factors would you expect a separate reference range for?

Answer 27

Gender, ethnicity, age.

Question 28

What are the reference limits on a reference range?

Answer 28

+ or - 2 Standard Deviations (top and bottom 2.5% are excluded). Therefore, values that fall outside the 95% are significant, even if they are healthy. 1 in 20 chance of having abnormal results for 1 factor.

Question 29

What is the equation for clinical specificity?

Answer 29

Clinical sensitivity = True positives / True positives + False negatives.

Question 30

What is the equation for clinical specificity?

Answer 30

Clinical specificity = True negatives / True negatives + False positives.

Question 31

What are specificity and sensitivity used for?

Answer 31

Sensitivity measures how likely is it that an individual has a disease, whereas specificity measures how likely it is that they do not have this disease.