Hypercalcaemia in Thyrotoxicosis- Twycross and Marks &UT= 703 Unfortunately, in most cases reported serial plasma calcium levels during treatment are not given. The relevant details in the present three cases, and six others in which the relevant information is available, are shown in Table II. In all but one the plasma calcium concentration had returned to normal within eight weeks of beginning treatment. Thus it would seem reasonable to wait at least this long before considering a second pathological condition to explain concomitant hypercalcaemia.