From the Guidelines
The most appropriate diagnostic test for this 18-month-old boy with status asthmaticus, recurrent infections, failure to thrive, postprandial vomiting, and a positive family history is the sweat chloride test. This patient presents with multiple symptoms highly suggestive of cystic fibrosis (CF): status asthmaticus (respiratory distress), frequent infections, failure to thrive (weight <5th percentile), post-feeding vomiting, and hepatosplenomegaly (HSM) [no direct evidence provided, but based on general medical knowledge]. The sweat chloride test is the gold standard diagnostic test for CF, measuring elevated chloride levels in sweat (>60 mmol/L in CF patients) 1. CF is an autosomal recessive disorder affecting the CFTR protein, which regulates chloride transport across epithelial cell membranes. This dysfunction leads to thick, sticky secretions in multiple organ systems, explaining the constellation of symptoms.
While the provided evidence focuses on asthma diagnosis in children aged 5-16 years 1, it does not directly apply to this 18-month-old patient. The European Respiratory Society clinical practice guidelines for the diagnosis of asthma in children aged 5-16 years recommend spirometry, BDR testing, and FeNO as the most widely available objective tests performed in patients under investigation for asthma 1. However, these guidelines are not relevant to this patient's age group or clinical presentation.
Given the patient's symptoms and family history, cystic fibrosis is a more likely diagnosis, and the sweat chloride test is the most appropriate diagnostic test. Early diagnosis through sweat chloride testing allows for prompt initiation of pancreatic enzyme replacement, nutritional support, airway clearance therapies, and potentially CFTR modulators, significantly improving outcomes.
Key points to consider in this diagnosis include:
- The patient's age and symptoms are not consistent with the asthma diagnosis guidelines provided 1
- The sweat chloride test is the gold standard for diagnosing cystic fibrosis
- Early diagnosis and treatment of cystic fibrosis can significantly improve patient outcomes
- The patient's clinical presentation is highly suggestive of cystic fibrosis, making the sweat chloride test the most appropriate diagnostic test 1.
From the Research
Diagnostic Considerations
The patient's symptoms, including status asthmaticus, recurrent infections, failure to thrive, postprandial vomiting, and a positive family history, suggest a possible diagnosis of cystic fibrosis (CF) 2, 3, 4.
Sweat Test as a Diagnostic Tool
The sweat test is considered the gold standard for diagnosing CF, with a chloride concentration above 60mmol/L being indicative of the disease 2, 5, 3, 4, 6. However, borderline values can make diagnosis challenging, and alternative diagnostic tests such as genotyping and electrophysiologic measurements may be necessary 2, 4.
Alternative Diagnostic Approaches
In cases where the sweat test is inconclusive, other diagnostic approaches can be considered, including:
- Genotyping to identify CFTR mutations 4
- Electrophysiologic measurements, such as nasal potential difference measurement or intestinal current measurement 2
- Evaluation of clinical symptoms and family history 3
Potential False Positives
It is also important to note that false positive sweat test results can occur in patients with other diseases, such as celiac disease, Klinefelter syndrome, and constipation treated with certain medications 6.
Diagnostic Algorithm
A diagnostic algorithm for this patient could involve:
- Initial sweat test to determine chloride concentration
- If the result is borderline or inconclusive, consider alternative diagnostic tests, such as genotyping or electrophysiologic measurements
- Evaluation of clinical symptoms and family history to support the diagnosis
- Consideration of other potential causes of symptoms, such as celiac disease or other gastrointestinal disorders 6