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To the Editor.
—Dr. Tenzel's observation concerning the findings of markedly elevated protein-bound iodine values (PBI) in patients with superior limbic keratoconjunctivitis (SLK) is most interesting. I have not performed this test routinely on patients with this condition but intend to from now on.One patient with SLK who had clinical findings suggesting hyperthyroidism did have a PBI of 11 μμg/100 cc, but results of her triiodothyronine (T3) suppression test were within normal limits. She was receiving estrogens which can raise the PBI findings as also, for example, do pregnancy and contraceptive pills. Another recent patient with SLK is under treatment for hyperthyroidism which she had for three years prior to onset of SLK. Other patients with SLK had low PBI findings suggesting hypothyroidism. Some of these are taking thyroid extract, like Dr. Tenzel's patient, but only in small amounts.I am deeply grateful to Dr. Tenzel for pointing