Comparative study of two methods of determining plasma and salivary theophylline

A new method for theophylline assay (Aris method), uses an immuno enzyme assay on a solid-phase (strips). We compared it to a HPLC method for 33 plasma samples and 85 saliva samples in children and adults. The correlation-coefficient between the two methods is highly significant (r = 0.976 for plasma samples and r = 0.99 for saliva samples) although we found a significant difference: the average difference is 0.789 microgram/ml for plasmatic levels and 0.55 microgram/ml for saliva levels. The values are rather low and remain widely satisfactory for posology adaptations. The reproducibility of the Aris method is similar to the HPLC method. Its sensitivity is quite satisfactory and can be improved. Yet the good correlations we obtained for plasma as well as for saliva, the rapidity, simplicity, specificity and low cost of this new technique should make the theophylline estimation easier in hospitals and laboratories.