SUMMARY. Parathyroid hormone (PTH) concentrations were compared in serum and EDTA plasma from 36 patients attending a renal stone clinic. Serum PTH concentrations ranged from 0·9 to 10·9pmol/L, with a mean of 4·6 pmoljL. When serum and EDT A plasma results were compared, in samples frozen within 30min of collection, EDTA plasma results were found to be significantly higher than those in serum (P

Parathyroid hormone (PTH) concentrations were compared in serum and EDTA plasma from 36 patients attending a renal stone clinic. Serum PTH concentrations ranged from 0.9 to 10.9 pmol/L, with a mean of 4.6pmol/L. When serum and EDTA plasma results were compared, in samples frozen within 30 min of collection, EDTA plasma results were found to be significantly higher than those in serum (P < 0.0001; Wilcoxon test), with an average increase of 19.5% over the serum result. Results from EDTA-preserved blood left to stand at room temperature for 48 h were on average 14.8% lower than results from the corresponding EDTA plasma samples frozen within 30 min, with highly significant difference (P < 0.0001). Freshly frozen serum and 48h EDTA plasma PTH results were not significantly different. Parathyroid hormone in EDTA-preserved blood is not completely stable, and this could lead to misclassification of results for samples which are not frozen quickly.

Regional Method• The ""Xenon inhalation method of measuring regional cerebral blood flow was applied in serial studies comprising 100 measurements in 57 cases of acute hemiparesis and hemiplegia presumed due to arterial occlusion. Satisfactory data for analysis were obtained in over 95% of the cases studied. Significant flow reductions in the ischemic hemisphere were demonstrated in the cases with more severe clinical disability. This study demonstrates the feasibility of applying this method for serial regional cerebral blood flow measurements in most cases of acute stroke. The expected clinical usefulness and limitations of the method are discussed.Additional Key Words papaverine hemiplegia arterial occlusion hypertension heparin hemiparesis• If the treatment of acute stroke is to be given a rational basis, and achieve a success comparable with that of myocardial infarction, a system must be developed with the essential capability of continuously monitoring or frequently measuring regional cerebral blood flow over a period of three or more days.The purpose of this paper is to report a preliminary experience with the 18J Xenon inhalation method, and to report the results of a feasibility study of the applicability of this method in often uncooperative acutely ill patients. In undertaking this study, a quantitative evaluation of the method itself was not intended, and new information about the pathophysiology of cerebral infarction was not expected. It will be seen that though the method is logistically formidable, its essential safety can facilitate study of critically ill patients. Provided its quantitative accuracy is confirmed in ongoing studies, some progress in the rational management of acute stroke can be hoped for.

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