Variability in cortisol assays creates an additional problem with setting criteria for a normal response to ACTH that apply to all centers. Two studies comparing cortisol results obtained with different assays showed a positive bias of radioimmunoassays and immunofluorometric enzyme assays of 10 to 50 percent compared with a reference value obtained using isotope dilution gas chromatography-mass spectrometry. As a result, in one study, depending on the combination of assay and criterion used, between 0 and 100 percent of healthy volunteers would be considered to have a normal response to ACTH. This illustrates the difficulty of interpreting cortisol responses that are close to the cutoff point. (3)
The National Heart, Lung, and Blood Institute (NHLBI) recommended dosing for systemic prednisone, prednisolone, or methylprednisolone in pediatric patients whose asthma is uncontrolled by inhaled corticosteroids and long-acting bronchodilators is 1–2 mg/kg/day in single or divided doses. It is further recommended that short course, or "burst" therapy, be continued until the patient achieves a peak expiratory flow rate of 80% of his or her personal best or until symptoms resolve. This usually requires 3 to 10 days of treatment, although it can take longer. There is no evidence that tapering the dose after improvement will prevent a relapse.