Which laboratory study would confirm the diagnosis of rheumatic fever?

DSSSB -28 August 2019 (Shift-2)

Medical & Surgical Nursing

Easy

Appeared in: DSSSB -28 August 2019 (Shift-2)

Explanation

The diagnosis of rheumatic fever requires evidence of a preceding Group A Streptococcal (GAS) infection, as per the Jones criteria.
Antistreptolysin O (ASO) is an antibody produced by the body in response to Streptolysin O, a toxin from GAS.
An elevated or rising ASO titre confirms a recent streptococcal infection, fulfilling an essential criterion for diagnosing rheumatic fever.
Typical positive cutoffs are often greater than 200 IU/mL in adults and greater than 300 IU/mL in children, though this can vary by laboratory.

Option A: Platelet estimation is a non-specific test. While platelets can be elevated (thrombocytosis) as part of the acute inflammatory response, this finding is not diagnostic for rheumatic fever.
Option B: Haemoglobin estimation is not a specific test for rheumatic fever. A low hemoglobin level (anemia) might be present due to chronic inflammation (anemia of chronic disease), but it does not confirm the diagnosis.
Option C: Red blood cell (RBC) count is a general blood test and is not used to diagnose rheumatic fever. It is part of a complete blood count (CBC) to assess for conditions like anemia or polycythemia.

Clinical Relevance

Nursing practice connection: Use the key finding related to Diagnostic laboratory investigations for Acute Rheumatic Fever (ARF) to guide bedside assessment, documentation, and the next nursing action.
Prompt and accurate diagnosis of rheumatic fever is critical to initiate treatment (antibiotics and anti-inflammatory agents) and prevent the most serious complication: rheumatic heart disease (RHD), which causes permanent valve damage.
Nurses play a key role in collecting blood samples for ASO titres, ensuring they are drawn at the correct time (acute and convalescent samples may be needed to show a rising titre), and monitoring the patient for major and minor criteria.
What if? If a patient presents with chorea (a major criterion) but has a normal ASO titre and ESR, the diagnosis of rheumatic fever can still be made. Chorea is a late manifestation, and by the time it appears, other inflammatory markers and ASO levels may have already returned to normal.

How to Approach the Question

First, identify the core of the question: it asks for a specific laboratory test to confirm a diagnosis.
Recall the underlying cause of rheumatic fever: it is an autoimmune reaction to a Group A Streptococcus infection.
Therefore, a confirmatory test must establish evidence of this preceding infection.
Evaluate the options. Platelet, hemoglobin, and RBC counts are general tests for inflammation or blood disorders, not specific to a streptococcal infection.
Recognize that the Antistreptolysin O (ASO) titre is the specific antibody test used to detect a recent streptococcal infection.
Conclude that the ASO titre is the correct answer as it provides the necessary evidence required by the Jones criteria for diagnosis.

Concept Tested & Keywords

Concept Tested: Diagnostic laboratory investigations for Acute Rheumatic Fever (ARF).
Stem keywords: laboratory study, confirm diagnosis, rheumatic fever
Lead-in keywords: Which

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