Possible diagnosis-Sweat Question

[poohmom66]

My 9 yr old daughter may have cystic fibrosis.  She had trouble with her merconium plug as an infant.  She has chronic constipation with foul smelling gas.  She has chronic sinus infections, asthma, and a hx of mycoplasma pneumonias.  Whe just had sweat chloride tests run on her last week.  The first test came back at 52.  The repeat was 62.  Her chest Xray showed some "air trapping", while her PFT's were normal.  Her sputum sample was negative.  We have sent blood work and stool samples, with no results at present.
My question is about the sweat chloride test.  If a child with the above history has high sweat chlorides - does that always mean CF?  If the genetics come back negative - does she still have CF?  Is the sweat chloride still the "gold standard"?  Is there instances where the sweat chloride can be unreliable?  The pulmonoligist is waiting to "diagnose" her.