Measurement of skeletal status after renal transplantation by quantitative ultrasound

Osteoporosis remains a major problem following kidney transplantation. Radiographic measures of bone mass are of limited predictive value after transplantation and are complicated by preexisting renal osteopathy. Quantitative ultrasound (QUS) is a new and non-invasive method to assess skeletal status, however, no data exist on ultrasonic bone parameter 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 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 parameters 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 +/- 22% compared to young adults, age-corrected CBS was decreased in NTP with 86 +/- 25% of normal, indicating a two-fold increased risk of fracture. SOS was 1525 +/- 47.7 m/s, BUA 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.

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 inter-feet variance of QUS results we suggest measurement of both ossa calcis to minimize measurement error after transplantation.