MLS Diagnostic Procedures & Reporting 4

Question 1

Which of the following is the preferred specimen for detecting Clostridioides difficile toxin?

Accepted Answer

Unformed (liquid or soft) stool

Answer

C. difficile testing should only be performed on unformed stool, as formed stool from asymptomatic carriers gives false-positive results and does not indicate active colitis.

Question 2

A prothrombin time (PT) is reported as an INR of 3.8 for a patient on warfarin therapy. The therapeutic range for most indications is 2.0–3.0. This result should be:

Accepted Answer

Reported as a critical value requiring immediate physician notification

Answer

An INR of 3.8 exceeds the typical upper critical threshold (often ≥4.0 or institution-specific), and supratherapeutic anticoagulation poses bleeding risk requiring prompt clinical notification.

Question 3

A positive DAT (direct antiglobulin test) with anti-IgG reagent, combined with a negative DAT with anti-C3d, is most consistent with:

Accepted Answer

Drug-induced immune hemolytic anemia or warm autoimmune hemolytic anemia

Answer

Warm AIHA and many drug-induced cases coat red cells with IgG without complement deposition, producing a positive anti-IgG DAT and negative anti-C3d DAT.

Question 4

A stool culture grows Salmonella typhi. Besides the clinical team, this result must be reported to:

Accepted Answer

Public health authorities, as it is a reportable pathogen

Answer

Salmonella typhi (typhoid fever) is a nationally notifiable disease in the US; laboratories are required to report positive cultures to local and state public health departments.

Question 5

In urinalysis, a positive nitrite test indicates the presence of:

Accepted Answer

Gram-negative bacteria that reduce nitrate to nitrite

Answer

The nitrite test detects bacteria (primarily Gram-negatives like E. coli) that convert dietary nitrate to nitrite via reductase enzymes; many Gram-positives lack this enzyme and produce a negative nitrite result.

(MLS) Medical Laboratory Scientist Practice Test

(MLS) Medical Laboratory Scientist Practice Test

MLS Diagnostic Procedures & Reporting 4