A nurse suspects that a six-month-old infant has cystic fibrosis. Which of the following tests will confirm t… - Haryana CHO - 2022

Haryana CHO - 2022

Child Health Nursing (Pediatrics)

Easy

Appeared in: Haryana CHO - 2022

Explanation

The sweat chloride analysis is the gold standard for diagnosing cystic fibrosis (CF).
CF is caused by a mutation in the CFTR gene, which leads to a dysfunctional CFTR protein that normally reabsorbs chloride in sweat ducts.
Failure of chloride reabsorption results in sweat with a high salt concentration.
A sweat chloride level of 60 mmol/L or greater is considered a positive result and confirms the diagnosis of CF.

Option A: This test confirms fat malabsorption (steatorrhea), which is a symptom of CF-related pancreatic insufficiency, but it is not specific to CF and can be caused by other gastrointestinal disorders.
Option B: Pulmonary function studies assess lung capacity and airflow. They are used for monitoring disease progression in older children, not for initial diagnosis. Furthermore, they are technically difficult and unreliable in a six-month-old infant.
Option D: Human Leukocyte Antigen (HLA) testing is completely unrelated to cystic fibrosis. It is used for tissue typing in transplantation and for diagnosing certain autoimmune conditions.

Clinical Relevance

Nursing practice connection: Use the key finding related to Diagnostic testing for Cystic Fibrosis to guide bedside assessment, documentation, and the next nursing action.
The nurse plays a key role in educating parents about the sweat test, alleviating their anxiety by explaining that it is a simple, non-invasive, and painless procedure.
Accurate diagnosis via the sweat test allows for early initiation of treatment, including pancreatic enzyme replacement, airway clearance techniques, and nutritional support, which is critical for improving long-term outcomes in CF.
What if the sweat test result is borderline (e.g., 45 mmol/L)? The nurse should anticipate that the physician will order a repeat sweat test and/or CFTR gene mutation analysis to confirm or rule out the diagnosis, and be prepared to explain this next step to the family.

How to Approach the Question

First, identify the core of the question: it asks for the confirmatory diagnostic test for cystic fibrosis.
Recall or look up the pathophysiology of cystic fibrosis, focusing on the defect in the CFTR protein and its effect on exocrine gland secretions, particularly sweat.
Evaluate each option based on this knowledge. The key is to find the test that directly measures the fundamental ionic abnormality of CF.
Eliminate the test for fecal fat because it measures a secondary complication (malabsorption) and is not specific.
Eliminate pulmonary function studies as they are for monitoring function, not for diagnosis, and are impractical in an infant.
Eliminate HLA testing as it is related to immunology and transplantation, not the genetics of CF.

Concept Tested & Keywords

Concept Tested: Diagnostic testing for Cystic Fibrosis
Stem keywords: six-month-old infant, cystic fibrosis, confirm diagnosis
Lead-in keywords: Which of the following tests
Clinical cues: Age/sex group narrows the expected diagnosis, intervention, or normal reference range.
Negative lead-in flag: false

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E6 Nelson Textbook of Pediatrics(2024) — Volume 2 pp. 456-458, 457-459

E6 Medicine Harrison 22e Part 2 p. 151-153