Which of the following is the Most Common Diagnostic Test for Cystic Fibrosis?

Uttarakhand CHO - 2021

Pathology & Genetics

Easy

Appeared in: Uttarakhand CHO - 2021

Explanation

The sweat chloride test is the gold standard for diagnosing Cystic Fibrosis (CF).
It directly measures the dysfunction of the CFTR protein, which is the underlying cause of CF.
In individuals with CF, the sweat glands cannot properly reabsorb chloride, leading to a high concentration of chloride in the sweat.
A chloride level of 60 mmol/L or higher is considered diagnostic for CF.

Option A: Liver function tests (LFTs) assess the health of the liver. While liver disease can be a complication of CF, LFTs do not diagnose the primary genetic condition.
Option C: Arterial Blood Gas (ABG) analysis measures the acid-base balance and oxygen/carbon dioxide levels in the blood. It assesses respiratory function but does not diagnose the cause of respiratory issues.
Option D: Pulse oximetry is a non-invasive method for monitoring a person's oxygen saturation. Like an ABG, it provides information about respiratory status but not the underlying diagnosis.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Diagnostic testing for Cystic Fibrosis as background academic context rather than a clinical decision trigger.
The sweat test is a fundamental diagnostic tool that nurses must be familiar with, especially in pediatrics and respiratory care.
Nurses play a key role in patient and family education, explaining that the test is painless (though it may cause a tingling or warm sensation) and preparing the child for the procedure to reduce anxiety.
Nursing responsibilities include ensuring the test site (usually the forearm) is clean and free of creams or lotions, which could interfere with the results.

How to Approach the Question

First, identify the core of the question: it asks for the 'most common diagnostic test' for a specific disease, Cystic Fibrosis.
Analyze the options provided. Categorize them in your mind: Are they diagnostic, monitoring, or screening tests?
Option A (Liver function test), C (ABG Analysis), and D (Pulse oximetry) are all tests that monitor body functions (liver, respiratory status, oxygenation). They are not typically used to provide a definitive diagnosis of a genetic disorder.
Option B (Sweat chloride test) is a specific test designed to detect a key pathophysiological feature of Cystic Fibrosis (abnormal chloride transport).
Recall or deduce that a diagnostic test must identify the underlying cause or a unique hallmark of the disease. The sweat test fits this description for CF.
Therefore, select the sweat chloride test as the primary diagnostic tool, distinguishing it from the other options which are used for monitoring complications or overall status.

Concept Tested & Keywords

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E6 Medicine Harrison 22e Part 2 p. 119-121

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 456-458