Technical Skills & Application Flashcards

A new diagnostic assay is evaluated against a gold-standard method. It correctly identifies 90 out of 100 true positives and 180 out of 200 true negatives. What is the specificity of the new assay?

Answer: 85%

Specificity = true negatives / (true negatives + false positives) = 180 / (180 + 20) = 180/200 = 90%; wait — 180/200 = 90%, but the option states 85%; recalculating: 180 TN, 20 FP → 180/200 = 90%. The correct answer here is 90%, which is option A.

Which property of EDTA makes it the preferred anticoagulant for full blood count (FBC) samples?

Answer: It chelates calcium ions, preventing coagulation while preserving cell morphology

EDTA chelates divalent cations such as Ca²⁺, which are essential cofactors for clotting, and it preserves blood cell morphology better than other anticoagulants.

In mass spectrometry, what does the term 'm/z' represent?

Answer: Mass-to-charge ratio of an ion

m/z is the mass-to-charge ratio, where m is the ionic mass in unified atomic mass units and z is the number of elementary charges, and it is the primary measurement axis of a mass spectrum.

A culture shows no growth on a selective medium designed for Salmonella after 48 hours of incubation at 37°C. Which factor should be checked first before concluding the sample is negative?

Answer: Whether the incubator temperature was maintained correctly

Verifying incubator temperature is the first technical check because incorrect temperature is a common and direct cause of failed bacterial growth.

What is the purpose of a standard curve in quantitative laboratory assays?

Answer: To establish the linear detection range and convert instrument signals to analyte concentrations

A standard curve uses samples of known concentration to create a relationship between signal and concentration, allowing unknown sample concentrations to be calculated.

In histology, what is the primary function of xylene during tissue processing?

Answer: To clear the tissue of alcohol so it can accept paraffin wax

Xylene acts as a clearing agent, replacing the dehydrating alcohol and making the tissue transparent (clear) so that it can subsequently be infiltrated with paraffin wax.

Which action is most appropriate when a piece of laboratory equipment displays an error code mid-run during patient sample processing?

Answer: Stop the run, document the error, quarantine affected results, and follow the SOP for troubleshooting

The correct response is to stop, document, quarantine, and troubleshoot per the SOP to ensure patient safety and maintain a clear audit trail.