The variation in urinary calcium levels in adult patients with fracture and surgical intervention

A total of 768 subjects (female = 271, male = 497, mean age = 46.69 ± 12.91, 18–97 years old) were enrolled in this study from 2012 to 2015. They were divided into two groups: group A and group B. Group A: 721 fracture patients (females = 309, males = 412, mean age = 46.60 ± 12.85 years) who underwent surgery within 1 week after fracture. Exclusion criteria were as follows: (1) patients who underwent fracture fixation through an emergency operation; (2) patients who were not admitted to hospital on the day of fracture; (3) patients in which an operation was not performed within a week after fracture; (4) patients who had multiple fractures, such as spinal fracture, rib fracture, pathological fracture, old fractures and delayed fracture healing or non-union; (5) patients who had any kind of fracture in the previous 3 months; (6) patients with a history of urinary calculus, parathyroid disease or renal chronic insufficiency. All the patients had surgery performed between 72 h and 7 days after fracture. Group B: 47 patients (females = 18, males = 29, mean age = 48.4 ± 13.98 years) without fracture in the present study, but who had undergone surgery for internal fixation in the previous 12 months. Exclusion criteria were as follows: (1) patients who had any kind of fracture in the last 3 months; (2) patients with a history of urinary calculus, parathyroid disease or renal chronic insufficiency. This study was approved by the ethics committee of Nanjing Drum Tower Hospital. The recruited subjects gave informed consent before commencing the present study.

For each patient, urine was collected over a 24-h period (24-h urine), using a jug that contained preservative (2 mL methylbenzene) to prevent bacterial growth. The initial urine was removed at 7:00 am, and the 24-h urine was collected in the jug until 7:00 am the next day. The 24-h urine samples were collected on the first day (d), third day, first week (week; first day after operation), third week, fourth week, sixth week, eighth week and twelfth week from fracture patients in group A. For patients in group B, 24-h urine samples were collected on the first day, third day, first week, third week, fourth week, sixth week, eighth week and twelfth week after hospitalisation. Subsequently, the urine calcium in the two groups was detected using a Vitros 350 autoanalyzer (Johnson-Johnson, NY, USA). The changes in urine calcium levels were evaluated according to fracture location, fracture type, age and gender. Additionally, the distribution of hypercalciuria in groups A and B at the different time points was also analysed.

Compared with group B, the level of urine calcium in group A was significantly increased at different time points during the study period (P < 0.05), except at the first w (P = 0.397). Additionally, in group A, we found that the level of urine calcium was up to 8.91 ± 5.26 mmol on the first day (Fig. 1), which fell to 5.48 ± 3.21 mmol after 1 week, and increased again to 7.96 ± 2.84 mmol in the fourth week. It then reduced to normal levels in the sixth week and maintained homeostatic levels from the sixth week to the twelfth week. The two higher concentrations were more than 7.5 mmol, indicating hypercalciuria. However, the variation in urine calcium levels in group B was different. In group B, the level of urine calcium showed a tendency to rise from the first day to the first week (4.49 ± 2.89 to 5.89 ± 3.42 mmol). It then reduced to a homeostatic level from the fourth week, and all levels were less than 7.5 mmol. Moreover, the distribution of hypercalciuria in groups A and B was analysed at different time points. We found that there were more patients with hypercalciuria in group A at different times compared with that in group B (Fig. 2, P < 0.001.

According to fracture location, all patients were divided into an upper limb fracture group (n = 202) and a lower limb fracture group (n = 519). The variation in urine calcium levels was similar between the upper limb fracture group and the lower limb fracture group. The level of urine calcium was up to 9.36 ± 5.59 mmol in the upper limb fracture group and 8.68 ± 3.01 mmol in lower limb fracture group on the first day (Fig. 3, P = 0.000), both fell to 5.64 ± 3.17 mmol and 6.55 ± 2.38 mmol after 1 week (P = 0.507), and again increased to 7.91 ± 2.77 mmol and 8.7 ± 2.36 mmol in the fourth week (P = 0.000), respectively. They both reduced to normal levels in the sixth week and maintained homeostatic levels from the sixth week to the twelfth week. The two higher concentrations in each group were both more than 7.5 mmol.

Based on the different fracture types, patients were divided into a cortical bone fracture group (n = 233) and an osteoporotic fracture group (n = 488). The variation in urine calcium levels was similar between the two groups. The level of urine calcium was up to 9.52 ± 5.59 mmol in the cortical bone fracture group and 8.62 ± 5.07 mmol in the osteoporotic fracture group on the first day (Fig. 4, P = 0.000). They both fell to 5.72 ± 3.14 mmol and 5.38 ± 3.23 mmol after 1 week (P = 0.281) and again increased to 7.79 ± 2.72 mmol and 8.04 ± 2.89 mmol in the fourth week (P = 0.000), respectively. They then reduced to normal levels in the sixth week and maintained homeostatic levels from the sixth week to the twelfth week. The two higher concentrations in the osteoporotic fracture group were more than 7.5 mmol, while only the concentration of urine calcium on the first day was more than 7.5 mmol in the cortical bone fracture group.

Based on their ages, all patients were divided into a young group (age < 60, n = 605) and an elderly group (age > 60, n = 116). The variation in urine calcium levels was similar between the two groups. The level of urine calcium was up to 8.72 ± 5.63 mmol in the elderly group and 8.95 ± 5.19 mmol in young group on the first day (Fig. 5, P = 0.000). They both fell to 5.37 ± 3.00 mmol and 5.51 ± 3.25 mmol after 1 week (P = 0.635) and again increased to 7.74 ± 2.74 mmol and 8.00 ± 2.85 mmol in the fourth week (P = 0.000), respectively. They then reduced to normal levels in the sixth week and maintained homeostatic levels from the sixth week to the twelfth week. The two higher concentrations in the young group were more than 7.5 mmol, while in the elderly group only the concentration on the first day was more than 7.5 mmol.

All patients were divided into a female group (n = 309) and a male group (n = 412), according to gender. The variation in urine calcium levels was similar between the two groups (Fig. 6). The two higher concentrations at the first day and the fourth week in males were more than 7.5 mmol, while only the concentration of urine calcium on the first day was more than 7.5 mmol in females. There was no significant difference between the female group and male group.