An epidemiological survey on serum strontium levels in renal failure patients in China

Objective: In a previous study we have reported a world-wide epidemiological survey on serum strontium (Sr) levels in dialysis patients in 23 countries. We showed that serum Sr levels greatly differed from country to country and roughly could be divided into 2 groups: centers with a mean serum Sr level > 100 µg/l and those with a serum Sr level < 100 µg/l. Furthermore, an association was reported between increased bone Sr concentrations and the development of osteomalacia. As the number of renal failure patients in China rapidly increases and data on Sr levels have not been reported so far, we assessed the serum Sr levels in Chinese renal failure patients. Material and methods: Serum samples of Chinese stable chronic renal failure (CRF) patients not yet on dialysis (n = 81), dialysis patients (n = 293), post-transplant patients (n = 60) and subjects with normal renal function (n = 62) were collected, as well as water and dialysate samples from 6 Chinese dialysis centers. For each patient a questionnaire with personal, clinical and dietary data was completed. In addition to Sr we also measured the aluminum and calcium content in the samples of dialysis patients. Serum Sr levels of the Chinese dialysis patients were compared to 172 serum samples taken from dialysis patients in Belgium, Portugal and Paraguay. All elements under study were measured by atomic absorption spectrometry. Results: The mean serum Sr level in subjects with normal renal function was 32.4 ± 10.5 µg/l. Stable CRF patients not yet on dialysis with a creatinine clearance (CrCl) >= 50 ml/min showed a mean Sr level of 46.6 ± 14.3 µg/l (n = 25) while those with a CrCl < 50 ml/min had a concentration of 57.7 ± 23.9 µg/l (n = 56) (p < 0.01). The overall mean serum Sr level of dialysis patients was 72.1 ± 17.1 µg/l (p < 0.01 vs. CRF not yet on dialysis). The mean serum Sr level in Chinese dialysis patients was significantly higher than that noted in Belgian (34.0 ± 7.9 µg/l) and Portugese (41.5 ± 9.2 µg/l) dialysis patients. Post-transplant patients with a CrCl >= 50 ml/min showed a mean Sr level of 49.6 ± 15.5 µg/l (n = 42) versus 61.3 ± 18.1 µg/l (n = 18) (p < 0.01) in those with a CrCl < 50 ml/min. Increased serum Sr levels in Chinese patients are possibly associated with a Sr-rich diet while in the subset of dialysis patients the Sr content of the final dialysate only seems to play a minor role. Conclusions: The serum Sr level significantly increases with decreasing renal function. Data of this multicenter study demonstrates serum Sr levels to be moderately increased in dialysis patients. Serum Sr levels in Chinese dialysis patients were significantly higher than those noted in Belgium and Portugal, however, remained below the arbitrary established high Sr cut-off level of 100 µg/l. To which extent the increased Sr levels may have any effect on bone metabolism needs to be further investigated.