Skeletal status after kidney transplantation by quantitative ultrasound: a 2-year follow-up study

Quantitative ultrasound (QUS) is a new and non-invasive method to assess skeletal status after kidney transplantation. We evaluated the potential use of this novel method in renal allograft recipients and studied the accuracy compared to normal controls. Thirty patients (NTP, age 47.5 ± 13.0 years) were studied 4.8 ± 3.2 years after kidney transplantation. Twenty-five healthy control persons (CON) were matched for age and sex. The left and right os calcis were studied by QUS, and speed of sound (SOS) and broadband ultrasound attenuation (BUA) were measured. Bone stiffness (BS) was calculated from these parameter and corrected for age (CBS). Differences between right and left os calcis were compared to CON to assess the side variability (mean ± SD); BS was 75 ± 25% compared to young adults, age-corrected CBS was decreased in NTP with 86 ± 25% of normal, indicating a 2-fold increased risk of fracture. SOS was 1,525 ± 47.7 m/s, BUA was 105 ± 22 dB/MHz. Mean difference between right and left os calcis was significantly higher in NTP than in CON (7.2 ± 7.1% vs. 2.1 ± 2.1%, p < 0.01). Limits of agreement of the measurements (MW of differences ± 2 SD) according to a Bland-Altmann type statistic were 16.9% and 20.7%. There was no correlation between CBS and age, cumulative steroid dose, parathyroid hormone concentrations or time after transplantation. In addition, 19 patients (49 ± 3 years, graft function: 1.8 ± 0.2 and 2.0 ± 0.2 mg%) were investigated in a 2-year follow-up study. The measures of bone stiffness at months 0 and 24 were well correlated (r < 0.9, p < 0.001), however, bone stiffness did not change significantly with time. There was a significant correlation between bone stiffness and serum calcium values (0.49, p < 0.015). Our data show altered bone structure expressed by low bone stiffness values measured by quantitative ultrasound in kidney transplant patients. However, because of relatively high interfeet variance of QUS, we suggest measurement of both os calcis to minimize measurement error after transplantation. In addition, we conclude from the data of this follow-up study that despite continued low-dose steroid treatment (< 10 mg prednisolone/day), renal transplant recipients are not subject to accelerated osteoporosis. Bone stiffness did not significantly decrease over 2 years in the present study. However, bone stiffness baseline and 2 years later were found to be decreased compared to healthy controls, a finding that is in accordance with previous data demonstrating an increased fracture rate in allograft recipients.