STP Technical Skills & Application 3

Question 1

A laboratory result shows an unexpectedly high potassium level of 7.2 mmol/L from a routine blood sample. What is the first pre-analytical variable to investigate?

Accepted Answer

Haemolysis of the sample

Answer

Haemolysis releases intracellular potassium from red blood cells, causing falsely elevated plasma potassium readings.

Question 2

In flow cytometry, what property of cells does forward scatter (FSC) primarily measure?

Accepted Answer

Cell size (relative volume)

Answer

Forward scatter correlates with cell size because larger cells diffract more laser light in the forward direction.

Question 3

Which technique is used to separate proteins based solely on their isoelectric point (pI)?

Accepted Answer

Isoelectric focusing (IEF)

Answer

In IEF, proteins migrate through a pH gradient until they reach the pH at which their net charge is zero (their pI), effectively separating them by pI.

Question 4

A scientist records duplicate OD readings of 0.452 and 0.468 for the same sample. What is the percentage difference between these readings?

Accepted Answer

3.5%

Answer

Percentage difference = |0.468 − 0.452| / ((0.468 + 0.452)/2) × 100 = 0.016/0.46 × 100 ≈ 3.5%.

Question 5

In ELISA, what is the function of the enzyme-conjugated secondary antibody?

Accepted Answer

It amplifies the signal by reacting with a substrate to produce a detectable product

Answer

The enzyme (e.g., HRP) conjugated to the secondary antibody converts a substrate into a coloured, fluorescent, or luminescent product, amplifying the detection signal.

(STP) Scientist Training Programme Practice Test

(STP) Scientist Training Programme Practice Test

STP Technical Skills & Application 3