We have investigated the effect of an acute phase response on the plasma concentrations of alpha-1-antitrypsin (α1AT) in various phenotypes. Ninety seven per cent of patients with an acute phase response or pregnant patients who had an MS, MZ, S or SZ phenotype had α1AT levels within or above the reference interval of patients with the M phenotype who did not have an acute phase response. Thus a ‘normal’ concentration of plasma α1AT cannot be used to exclude even an S or SZ phenotype if the patient is pregnant or has an acute phase response.
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