Sweat testing and cystic fibrosis – Test performance before and after a quality improvement project in a South African tertiary hospital laboratory

Abstract

Background

The diagnosis of cystic fibrosis (CF) is challenging due to high quantity not sufficient (QNS) rates of sweat tests, leading to frequent retesting, increasing costs and adverse impacts on patient care. This study aimed to assess sweat test performance and implement a quality improvement project (QIP) to reduce QNS rates.

Methods

A two-part retrospective audit was conducted. Part one spanned 2 years reviewing the two-tiered testing with sweat conductivity as a screening tool, followed by chloride testing. Part two evaluated the QNS rates over two 6-month periods, separated by a QIP, which involved technologist training, clinician education, patient preparation protocols and revised testing procedures.

Results

Over the 2-year period, 425 sweat tests were performed on 291 patients. Sweat conductivity testing demonstrated a lower QNS rate, 13% (31/238), compared to sweat chloride testing’s 31% (33/105). High QNS rates were observed in younger infants and in malnourished or acutely ill patients. Post-QIP, the QNS rates for the total study population decreased by 5%, from an initial 30% to 25% in the sweat chloride cohort, while the acceptable QNS rate of 12% remained unchanged in the sweat conductivity cohort.

Conclusion

Achieving target QNS rates remains challenging, especially in younger infants, with improved QNS rates in older infants and children. Recommendations include limiting sweat testing to experienced technologists and ensuring patient readiness.