Technical aspects of histamine determination in human tears

We evaluated various technical aspects of tear collection to assess their influence on the measurement of tear histamine levels. We included several methods of collecting tears, storage of tears with and without freezing, storage for three vs ten days, and removal vs nonremoval of cells before freezing. We assayed tear samples in various groups of people with inflamed eyes. None of the various means of collecting or storing the tear samples influenced the histamine measured. The measuring technique is a stable one that requires minimal treatment of samples before assay. To date, we have found that only patients with vernal conjunctivitis have elevated tear histamine levels. Any increase of tear histamine over 10 ng/ml (geometric mean plus 2 S.D.) or any significant decrease is probably related to the disease itself and not to factors related to the technique used to measure tear histamine.