What is the role of immunoreactive trypsinogen (IRT) measurement in the workup of cystic fibrosis (CF)?

Updated: Sep 28, 2020
  • Author: Girish D Sharma, MD, FCCP, FAAP; Chief Editor: Kenan Haver, MD  more...
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Immunoreactive trypsinogen (IRT) is a pancreatic enzyme that can help with diagnosing CF in neonates with meconium ileus when IRT relative ratios are elevated greater than the 99th percentile. IRT plus sweat test was shown to increase sensitivity and specificity in screening.

In a study by Steven et al, only 2 of 29 patients with intestinal obstruction from meconium ileus had a normal IRT relative ratio, supporting a false-negative rate of 7%; however, when checked at days 9 and 12, the IRT relative ratio was elevated above the 99th percentile. IRT levels cannot be used to differentiate between simple and complicated meconium ileus. [53]

Monitoring the detectability of IRT over the first 5 years of life has also shown that the eventual absence of this enzyme correlates with severe CF. This finding is also indicative of a negative correlation between the start of pancreatic enzyme replacement and the end of IRT detectability. [54]

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