Abstract
Serum calcium and phosphorus concentrations, alkaline phosphatase activity and the metacarpal bone mass were measured in 85 female inhabitants of the cadmium-polluted Jinzu River basin aged 55-71 years who had various concentrations of β2-microglobulin (β2-m) in urine. The relationship between cadmium-induced renal tubular dysfunction and abnormalities of calcium and phosphorus metabolism was studied.
1) Most of the values for serum calcium were within the normal range. However, fractional calcium excretion (FEca) was increased in 81 subjects (95.3%). The correlation coefficient between urinary excretion of β2-m and FEca was significant (r=0.352, p<0.005).
2) Serum phosphorus concentration averaged 3.16±0.48ml/dl and the values found in 28 subjects (32.9%) were below the normal lower limit (3.0mg/dl). There was a significant correlation between serum phosphorus level and TmP/GFR (r=0.797, p<0.001). These observations show that hypophosphatemia is due to excessive renal phosphate excretion.
3) Serum alkaline phosphatase activity was definitely elevated in 29 subjects (34.1%). A significant positive correlation of alkaline phosphatase activity and urinary β2-m level was present (r=0.346, p<0.005).
4) The metacarpal index (MCI) and ΣGS/D of the second right metacarpal bone were measured by the quantitative microdensitometric method. A significant negative correlation of the urinary β2-m level with MCI and ΣGS/D was present (p<0.01). This result suggested that the degree of renal tubular dysfunction was related to the bone mass.
5) This study showed that the inhabitants with severe renal tubular dysfunction had hypophosphatemia due to excessive renal phosphate excretion, increased urinary excretion of calcium, elevated activity of serum alkaline phosphatase and decreased bone mass. We proposed that these cases be diagnosed as latent renal tubular osteomalacia.
