Intro to diagnostic testing

Question 1

Name 5 uses of investigations

Answer 1

1) Diagnosis
2) Suitability for treatment
3) Prognosis
4) Monitoring of treatment
5) Screening

Question 2

Why should you not do irrelevant investigations?

Answer 2

Irrelevant investigations lead to unnecessary risk, cost and false positive results. Access – is the equipment there, are there other patients with higher priority?

Question 3

When and how should you use investigations?

Answer 3

Should be requested after you have clinically assessed the patient
The information you gain must outweigh the risk to the patient
Investigations should start with the least invasive and least risky and move up

Question 4

Name the different liver blood tests and when they may be abnormal

Answer 4

Albumin – major component of total blood protein, made specifically by the liver; decreased in chronic liver disease

Aminotransferases – found in the liver and elsewhere; very high levels in the blood usually indicate liver damage. Related to amino acid metabolism. Should be staying in the liver therefore high levels in the blood indicate liver damage.

Bilirubin – breakdown product of heme, usually cleared by the liver; elevated levels suggest liver disease

Alkaline phosphatase – found in the liver and elsewhere; blood levels may be increased in acute viral hepatitis

Gamma glutamyl transferase – found in the liver and elsewhere; blood levels may be increased in hepatitis and chronic liver disease. Transfers glutamate groups.

Question 5

What are urea and electrolytes measured for?

Answer 5

Urea – produced in the liver and removed from the blood by the kidneys; increased levels suggest kidney problems. Indicative of kidney problems rather than liver problems

Electrolytes – Na+, K+, Cl- and bicarbonate; various imbalances with different causes; linked to acid-base balance (blood pH); can be used to monitor the effects of treatment

Question 6

What things are measured in a full blood count?

Answer 6

Haemoglobin (Hb) – concentration of haemoglobin in the blood; lowered in anaemia - lowered ability of the blood to carry oxygen because there is less haemoglobin.

Haematocrit / PCV – packed cell volume, proportion of blood volume made up of cells

Red cell count (RCC) – estimated number of red blood cells; can differentiate between different types of anaemia

Mean corpuscular volume (MCV) – average volume of the red blood cells; changes of size in either direction can differentiate between different types of anaemia

Mean corpuscular haemoglobin (MCH) /
Mean corpuscular haemoglobin concentration (MCHC)

White blood cells (WBC) / Platelets – refers to immune response. Will have elevated WBC during infection.

Question 7

What is PCR?

Answer 7

PCR is a way of exponentially replicating a specific DNA sequence, making small quantities detectable
Some DNA sequences are highly specific to a particular pathogen, so detection of these sequences can make a good diagnostic test
‘Primers’ are produced that are complementary to these sequences and are used in PCR tests for that pathogen. Have to know what you’re looking for.
These tests are useful for rapid and early detection of pathogens, especially when small numbers of organisms are present or when other techniques not feasible