A 40-year-old lady came into the hospital with fever and rashes for a few days and is suspected to have Dengue. Which test would show that her fever is due to this disease?

Appeared in: RML 2023

Explanation

The NS1 (Non-Structural Protein 1) antigen is a viral protein that is abundant in the blood during the early, acute phase of a dengue infection, typically within the first 7 days of fever.
Detection of the NS1 antigen is highly specific for dengue virus, making it a reliable confirmatory test for an active, ongoing infection.
Since the patient has had symptoms for a 'few days', she is in the ideal window for NS1 antigen detection.
Unlike antibody tests which reflect the body's immune response, the NS1 test directly detects a part of the virus itself.

Option A: The presence of IgG antibodies indicates a past dengue infection or a secondary infection, not necessarily the current acute illness. IgG antibodies appear later in the course of the disease and can persist for life.
Option B: Thrombocytopenia (a low platelet count) is a characteristic feature of dengue fever, especially during the critical phase, but it is not a specific diagnostic test. Many other conditions, such as malaria, leptospirosis, and other viral infections, can also cause thrombocytopenia.
Option D: A low Total Leucocyte Count (TLC), or leukopenia, is a common finding in the early febrile phase of dengue. However, like thrombocytopenia, it is non-specific and can be seen in many other viral illnesses, such as influenza and measles.

Clinical Relevance

Nursing practice connection: Knowing Diagnosis of acute Dengue fever using laboratory tests helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Early and accurate diagnosis of dengue using the NS1 test is crucial for appropriate patient management, including monitoring for warning signs of severe dengue (e.g., severe abdominal pain, persistent vomiting, fluid accumulation, mucosal bleeding).
Prompt diagnosis allows nurses to initiate supportive care, such as ensuring adequate hydration and advising against the use of NSAIDs (like Aspirin or Ibuprofen) which can increase bleeding risk.
What if? If the patient presented 10 days after the fever started, the NS1 antigen test would likely be negative. In this later stage, an IgM antibody test (MAC-ELISA) would be the more appropriate diagnostic tool to confirm a recent dengue infection.

How to Approach the Question

First, analyze the question's core requirement: to find a confirmatory test for an acute illness.
Next, evaluate the clinical information provided: the patient has had a 'fever and rashes for a few days', which points to the early phase of an infection.
Consider each option's role in diagnosis. Differentiate between tests that detect the pathogen directly (antigen) versus those that detect the body's response (antibodies) or non-specific changes (blood counts).
The NS1 test detects a viral antigen, making it a direct and early marker of infection.
IgG antibodies indicate past exposure, not necessarily the current cause of fever.
Thrombocytopenia and low TLC are non-specific signs, not confirmatory tests.

Concept Tested & Keywords

QxherTa3lSR48zUsKKZkeA

E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart B (pp 202-403 of 604) p. 107-109

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 2076-2078

E6 Medicine Davidson Principles Practice 24e p. 264-266

Practise the full RML 2023

Attempt every question from this paper in a timed mock, then review the full solution for each one.