Platelet Na+,K+-adenosine triphosphatase as a tissue marker of hyperthyroidism

Platelet Na+,K+-adenosine triphosphatase (ATPase) activity was measured in 34 (15 males, 19 females) healthy subjects, 89 (35 males, 54 females) hyperthyroid patients, and 34 (7 males, 27 females) treated hyperthyroid patients to assess the potential of this measurement as a tissue marker and diagnostic test for hyperthyroidism. Platelet Na+,K+-ATPase activity was measured in platelet lysates by the rate of release of phosphate from adenosine triphosphate (ATP) in the presence and absence of ouabain. Platelet Na+,K+-ATPase activity (median and range) in the hyperthyroid group (271, 169 to 821 pmol/h/g protein) was significantly higher compared with the healthy group (125, 74 to 185 mu mol/h/g protein, P<.001 by Mann-Whitney U test). The treated hyperthyroid group had slightly, but significantly higher, free triiodothyronine (FT3) and free thyroxine (FT4), as well as platelet Na+,K+-ATPase activity (147, 98 to 246 <mu>mol/h/g protein, P<.05). If a platelet Na+,K+-ATPase activity of 190 <mu>mol/h/g protein was used as a cut off value, the specificity and sensitivity were 90% and 93%, respectively. We conclude that platelet Na+,K+-ATPase may be a useful tissue marker of hyperthyroidism. Copyright (C) 2001 by W.B. Saunders Company.