Abstract and Introduction
Patient: 1-month-old male.
Chief Complaint: Multiple positive sweat chloride tests in the absence of signs or symptoms suggestive of cystic fibrosis (CF).
History of Present Illness: The patient was referred for sweat chloride testing after a positive newborn screen for immunoreactive trypsinogen (IRT). Immunoreactive trypsinogen is suggestive of CF when the value is within the top 5% of a period-specific floating cutoff value (Figure 1). The patient's sweat chloride levels were elevated (>60 mmol/L). Preliminary screening for CF transmembrane conductance regulator (CFTR) mutations using a 40 mutation screen identified 1 mutation in intron 11 (1585 -1G>A, legacy name 1717 -1G>A). Subsequent full gene CFTR sequencing revealed a second CFTR mutation in intron 22.
Past Medical History: The infant was full term, weighing 8 lbs 6 oz at birth, and experienced an uncomplicated delivery. The infant was discharged following a standard 2-day stay in the newborn nursery.
Physical Exam: A temperature of 36.4°C (axillary), blood pressure of 120/80 mm Hg, heart rate of 148, and respirations of 40 per minute were measured for the patient. The patient's O2 saturation was 100% on room air. The patient's length was 61.2 cm (90th percentile), weight 6.27 kg (95th percentile), and head circumference was 39.7 cm (50th percentile). His weight-to-length ratio was at the 50th percentile. The patient appeared healthy with no labored respiration and no apparent digestive issues.
Drug History: None
Family History: No family history of chronic diseases.
Principal Laboratory Findings: The patient underwent sweat chloride testing on sweat collected by pilocarpine iontophoresis from both arms (Table 1). These tests were repeated several weeks later yielding similar results (not shown).
Lab Med. 2012;43(2):1-5. © 2012 American Society for Clinical Pathology