Clinical Assessment of Bone Mineral Status
Mary Leonard (Childrens Hospital of Pennsylvania)
Dr. Leonard is one of the leaders in investigating non-invasive methods for determining bone status in CKD patients. She started her presentation by reminding all of us of the dangerous misinterpretations that come from using serum iPTH levels. Even though iPTH is easy to measure (though somewhat harder today with the bundle payment system), data simply do not indicate that it is a reliable marker for the type and severity of renal osteodystrophy present. As a result, an “optimal” iPTH level has still not been established.
In the early days of CKD-BMD research, prominent physician groups such as K/DOQI recommend the use of DEXA scans in CKD patients. This may have made sense as we use DEXA scans in at-risk non-CKD patients. Data now show 2 major pitfalls in using DEXA reliably in CKD patients: 1) DEXA scans superimpose vascular calcification onto the bone images, and can result in falsely higher z-scores, and 2) DEXA scans cannot differentiate disease between trabecular and cortical bone. Dr. Leonard mentioned one study that doomed DEXA from being used in CKD patients, showing that the ROC AUCs for detecting a fracture in the spine (0.6), femur (0.4), and hip (0.6) were essentially “worthless”.
***Note: The closer your ROC AUC is to 1.0, the better a diagnostic test you have. The closer your ROC AUC is to 0.5, the more likely your test has a 50/50 chance of identifying disease (a coin flip).
What do can we use if we don’t want to rely on the bone biopsy? There are 2 tests in the horizon that show promise. The first is the peripheral quantitative CT (and it’s high-resolution cousin) (HRpQCT). Found in only 7 North American centers, the ROC AUC for detecting fracture in the spine, femur, and hip ranges from 0.73-0.79. Dr. Leonard is working with HRpQCT as well as micro-MRI and is finding much better ROC AUCs than DEXA scanning.
We’ll have to stay tuned for more data to know if we’ve finally found a reliable non-invasive method for assessing bone mineral status.
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