Question

The physician has ordered a sweat test for a child suspected of having cystic fibrosis. A positive sweat test is based on: A. Chloride level B. Potassium transport C. Serum sodium D. Calcium level

Short answer

Answer: A. Chloride level

Step-by-step solution

Understanding the options

First, let us briefly analyze each substance mentioned in the options: A. Chloride level B. Potassium transport C. Serum sodium D. Calcium level

Identifying the correct factor for a positive sweat test

To determine the correct answer, recall that a sweat test is a diagnostic test for cystic fibrosis, which is characterized by the defective transport of chloride and other ion channels, leading to an excess of salt in the sweat. Hence, among the given options, the correct factor for a positive sweat test is: A. Chloride level The high levels of chloride in the sweat are indicative of a positive sweat test, and this is used to diagnose cystic fibrosis in children.

Key concepts

Sweat Test

The sweat test is a common and effective method used to diagnose cystic fibrosis (CF). It measures the amount of chloride in the sweat. This test is simple, painless, and highly accurate.

To perform a sweat test, a small amount of a sweat-inducing substance, usually pilocarpine, is placed on the skin. Then, the area is stimulated with a mild electric current to produce sweat.

After the sweat is collected, the chloride concentration is measured. High levels of chloride are indicative of cystic fibrosis. This happens because CF affects the transport of chloride ions, leading to saltier sweat.

If a child shows symptoms of CF or if there's a family history, doctors often recommend this test. The results help confirm the diagnosis and guide treatment options.

Chloride Level

Chloride level in the sweat is the primary measure in a sweat test. When a child undergoes this test, the central focus is on the amount of chloride present in their sweat.

For children, a chloride level of greater than 60 mmol/L is highly suggestive of cystic fibrosis. Levels between 30-59 mmol/L may be borderline and other diagnostic tools might be needed to confirm. A level below 30 mmol/L is generally considered normal.

These levels are important because, in normal conditions, sodium and chloride ions from sweat are reabsorbed into the skin. In cystic fibrosis, this reabsorption process is impaired, leading to higher concentrations of chloride in the sweat.

Tracking chloride levels not only helps in diagnosing CF but also in monitoring the effectiveness of ongoing treatments.

Pediatric Diagnostic Tests

In pediatrics, diagnosing conditions early is crucial to effective treatment. Pediatric diagnostic tests are tailored to address conditions common in children. The sweat test is a prime example of a pediatric test used to diagnose cystic fibrosis, often observed in early childhood.

Pediatric tests are generally non-invasive and designed to cause minimal discomfort. They include a variety of methods from physical examinations to laboratory tests like blood work and genetic testing.

The sweat test stands out due to its specific application to CF. It is a painless procedure, which is a significant advantage when dealing with young patients who may be fearful or uncooperative.

By using such tests, clinicians can provide accurate diagnoses and begin treatment plans tailored to children's unique needs, ensuring that children receive the best care possible right from the start.