Sweat conductivity for diagnosing cystic fibrosis after positive newborn screening: prospective, diagnostic test accuracy study

Rate and predictors of insufficient sweat volume in very young infants after pilocarpine gel iontophoresis: prospective, population-based study

OBJECTIVE

To verify the rate and predictors of 'quantity not sufficient' (QNS) among Brazilian infants younger than 3 months with positive newborn screening (NBS) for cystic fibrosis (CF).

DESIGN

Prospective, population-based study.

SETTING

Public Statewide Newborn Screening Programme where the incidence rate of CF is ≈1:11 000.

PATIENTS

Subjects with positive two-tiered immunoreactive trypsinogen.

INTERVENTIONS

Sweat induction and collection were performed in the same facility; one sweat sample was obtained per individual.

MAIN OUTCOME MEASURES

The QNS rate and its predictors; analysis corresponded to the day of sweat collection.

RESULTS

Among the 975 participants, QNS rates for 10 and 15 µL were 3.6% (95% CI 2.5% to 4.9%) and 8.3% (95% CI 6.6% to 10.2%). Infants weighing >3056 and >3845 g and with gestational age higher than 37 weeks had a greater likelihood (5.5 and 6.7, and 2.7 and 5.8 times more, respectively) of avoiding QNS than their peers.

CONCLUSION

QNS rates fulfilled the requirements, but predictors differed from those recommended by the Cystic Fibrosis Foundations guidelines.

Sweat conductivity diagnostic accuracy for cystic fibrosis: a systematic review and meta-analysis

OBJECTIVE

We conducted a systematic review and meta-analysis of diagnostic test accuracy studies to summarise the properties of sweat conductivity (SC) to rule in/out cystic fibrosis (CF).

DATA SOURCE

We searched PubMed, Embase, Web of Science, Google Scholar, SciELO and LILACS up to 13 March 2023.

STUDY SELECTION

We selected prospective and retrospective diagnostic test accuracy studies which compared SC, measured through two well-established and commercially available devices, that is, Nanoduct or Sweat-Chek Analyser, to quantitative measurement of sweat chloride.

MAIN OUTCOME MEASURES

Pooled sensitivity, specificity, positive likelihood ratio (+LR) and negative likelihood ratio (-LR), and their corresponding 95% CIs.

DATA EXTRACTION AND SYNTHESIS

The Preferred Reporting Items for a Systematic Review and Meta-analysis of Diagnostic Test Accuracy Studies guidelines were followed. Data were extracted by one reviewer and checked by another. The hierarchical summary receiver operating characteristics model was used to estimate diagnostic test accuracy.

RESULTS

Ten studies involving 8286 participants were included. The pooled estimates of sensitivity, specificity, +LR and -LR were 0.97 (95% CI 0.94 to 0.98), 0.99 (95% CI 0.98 to 0.99), 171 (95% CI 58 to 500) and 0.02 (95% CI 0.01 to 0.05), respectively. Sensitivity analyses did not reveal a substantial impact of study-level factors on the results, such as study quality, cut-off values for a positive test, study sample size and participant age group. The quality of evidence was considered moderate.

CONCLUSION

SC demonstrated excellent diagnostic performance. In addition, its accuracy parameters suggest its role as an alternative to the sweat test for CF diagnosis.

PROSPERO REGISTRATION NUMBER

CRD42022284504.