CKD-MBD

Clinical information

Chronic kidney disease (CKD) is an important public health problem affecting 5% to10% of the world’s population with growing global burden. CKD is defined as abnormalities in kidney structure or function (or both) that are present for more than three months and have health implications. The disease is further classified based on cause, glomerular filtration rate (GFR) and extent of albuminuria. As kidney function decreases, marked changes in bone and mineral metabolism occur, leading to a constellation of bone lesions referred to as renal osteodystrophy (ROD). Chronic kidney disease–mineral and bone disorder (CKD–MBD) is a systemic disorder characterised by a combination of:  

• biochemical abnormalities – including calcium, phosphate, PTH, or vitamin D metabolism disorders;  
• bone abnormalities – in turnover, mineralization, volume, or strength; and, 
• vascular calcification 

These three interrelated processes account for the morbidity and mortality in CKD; therefore, early recognition is essential to initiate appropriate management.  

Diagnostics

The biochemical, hormonal and mineral irregularities, bone disorders and extraskeletal calcification should all be addressed for the diagnosis and management of CKD–MBD.  

Treatment decisions should not be based on a single laboratory value but on trending of serial measurements of phosphate, calcium and PTH considered together, as therapy for one abnormality could also affect others. 25(OH)D levels might be measured with repeated assessments depending on baseline values and therapeutic interventions. 

Bone biopsy is the gold standard for CKD-associated osteoporosis in CKD patients; however, the procedure is invasive and cumbersome. Recent studies have indicated that the use of certain bone turnover markers (BTMs) may prove beneficial to assess bone turnover and support monitoring of CKD–MBD therapies. Due to the reduction in kidney function, it is important to use markers of bone turnover that are not excreted by the kidneys such as: 

• bone alkaline phosphatase (BAP) 
• intact propeptide of type I collagen (PINP) and  
• tartrate-resistant acid phosphatase 5b (TRAcP 5b).

Matrix γ-carboxyglutamatic acid (Gla) protein, or matrix Gla protein (MGP) for short, is one of the most well-known inhibitors of vascular and tissue calcification. Increased dephosphorylated-uncarboxylated MGP (dp-ucMGP) levels are considered a risk marker for cardiovascular diseases. Regular monitoring of the dp-ucMGP level may help to assess the risk of vascular complications in elderly people who are prone to atherosclerosis as well as in CKD patients.