Choose the defensible disposition

Use the first collection to separate an analyzable result from a QNS specimen. The 48 mmol/L right-arm result is intermediate and needs repeat sweat testing. The 9-microliter left-arm specimen has no chloride result because it did not meet the collection minimum. The correct first laboratory action is to report both dispositions accurately and support repeat evaluation.

Now consider the contrast branch. If repeat adequate sweat chlorides are 34 and 38 mmol/L and only one CF-causing variant is confirmed, the pattern meets the CRMS or CFSPID definition rather than confirming CF. CFF 2024 guidance includes repeat sweat testing at 6 months and then at least annually to age 8, with genetic follow-up such as phasing and sequencing as indicated. A variant classification alone does not supply a diagnosis.

Two variants matter differently when they are in trans, on opposite chromosome copies, than when they are in cis. Phasing can require parental or other family testing; the laboratory reports the observed evidence and routes intermediate or discordant results through the established CF-center and genetic follow-up pathway.