Limitation of the Vitros dry-slide technique in measuring high concentrations of salicylate in plasma.

The linearity of the Vitros dry-slide method for plasma salicylate was assessed in two ways: serial concentrations of sodium salicylate were added to fresh lithium heparin plasma, and the salicylate was determined both neat and in dilution. Vitros salicylate results submitted to the Heathcontrol External Quality Assessment Scheme were compared to the spike value. Similar loss of linearity was observed in both cases. Serious salicylate overdosage requiring specific clinical treatment may have been underestimated.