214 D. A. Smith, J. C. Mackenzie: Calcium Clearance and Re-absorption in Patients 



parathyroidism and those with osteoporosis, this being more apparent at higher levels 

 of ultrafilterable calcium. Fig. 2 shows the distribution of the data obtained in the 

 patients with renal stone disease with the 95''/o confidence limits. 



In Fig. 3 the re-absorption of calcium per 100 ml of filtrate is related to the 

 plasma ultrafilterable calcium in patients with osteoporosis and renal stone. The 

 re-absorption of calcium in patients with renal stone is significantly lower than in 

 the osteoporotic group, especially at the higher levels of plasma ultrafilterable cal- 

 cium. It is also evident that the maximum tubular re-absorption of calcium is ap- 

 proached only in the patients with renal stone, and this occurs at about a value of 

 6 mg per 100 ml of glomerular filtrate. Fig. 4 shows the tubular re-absorption in the 

 osteoporotic and hyperparathyroid patients. The tubular re-absorption is slightly 

 higher in patients with primary hyperparathyroidism. It is evident that a maximum 

 tubular re-absorption of calcium has not been reached in the hyperparathyroid 

 patients. 



The percentage re-absorption of calcium falls in all three groups of patients as 

 the plasma calcium rises during calcium infusion, a typical example being shown 

 from each group in Table 1. 



Table 1 



°o Keabsorp- 

 tion of calcium 



A. M. 



A. S. 



H. C. 



Osteoporosis 



Renal stone disease 



Primary hyperparathyroidism 



95.9 

 94.6 

 92.7 

 90.6 

 90.2 

 87.2 

 85.8 

 91.2 

 91.3 

 87.3 

 85.6 

 84.0 

 74.0 

 77.0 

 95.5 

 94.0 

 90.0 

 87.0 

 85.6 



Discussion 



The lowered calcium clearance and slightly raised calcium re-absorption in 

 patients with primary hyperparathyroidism would tend to support the evidence of 

 Kleeman et al. (1958) and Bernstein et al. (1963). The increased calcium clearance 

 and decreased re-absorption in patients with renal stone disease has not been 

 described before, and strongly suggests a specific tubular resorptive defect for calcium. 

 In contrast to the findings of McPherson (1959), it is only in this group that a Tm 

 for calcium was approached. Since the calcium clearance and re-absorption is so differ- 

 ent in patients with renal stone disease and primary hyperparathyroidism, it is 

 suggested that the estimation of calcium clearance during a calcium gluconate in- 



