1. Chronic Kidney Disease-Mineral and Bone Disorder
Caitlin Musser and Carmen Young
Introduction
Chronic kidney disease is commonly linked with mineral and bone disorder (CKD-MBD). This association is because of the kidneys’ role in maintaining bone mass. In the case of chronic kidney disease CKD, the kidneys struggle to filter calcium and phosphorus. This leads to the inability to regulate adequate levels in the blood. Bone hormone levels become unregulated and abnormal. Due to the kidneys inability to properly maintain mineral and hormone levels, many patients with CKD develop CKD-MBD. Almost all CKD patients on dialysis will experience irregular mineral levels and will progress to CKD-MBD. The lack of mineral regulation in the bones can also cause renal rickets in children. Frequently, bone changes can appear before symptoms of kidney disease are presented. Overall, CKD-MBD results in weak, thin bones. Nutrition is an important component in maintaining appropriate mineral balances and preventing severe weakening of the bones. Registered dietitians can provide CKD-MBD patients with education and meal plans to prevent disease advancement.
Cardiovascular Risk and Manifestations
Studies show CKD can result in loss of myotubes prompt interstitial myofibroblasts from low vitamin D levels (calcitriol) and high phosphate levels2.
These abnormal levels lead to calcification of smooth muscle and vascular cells2.
Calcification increases as kidney function decreases and Greatly increased risk of cardiovascular disease2.
Newer research shows a greater response to treatment in the older population than children and young adults3
Vitamin D analogs
Non-calcium-containing phosphate binders
Cinaclcet
The abnormal metabolism of calcium, phosphorus, PTH and vitamin D can result in irregular changes and turnover in bones7.
Summary
Calcium, phosphorus, and vitamin D levels are all related in regards with PTH and CKD-MBD.
Research shows a strong association between CKD-MBD and increased risk of cardiovascular disease
Calcification of smooth tissues should be monitored
Treatment of CKD-MBD crucial in prevention of cardiovascular disease and increased morbidity and mortality
Diagnosis of the condition and evaluating is done through blood screening and bone biopsy
It is important to manage CKD to prevent the weakening of bones.
CKD patients should minimize other CVD risk factors
Registered Dietitian
Interpret nutrient lab levels
Educated patient on food choices that improve lab values
Monitor vitamin D, calcium & phosphorus intake, and consider supplementation
Educate patient on proper protein intake & weight management
CKD-MBD
Biochemical abnormalities
Bone abnormalities
Soft tissue and vascular calcification
Importance of Minerals and Hormone Levels
The kidneys balance calcium, phosphorus, and vitamin D in the blood.
When calcium is too low, parathyroid hormone (PTH) is released from parathyroid glands and stimulates calcium release from bones to the blood1.
When phosphorus becomes too high in the blood, calcium in the blood is lower2.
PTH increases and leads to calcium drawn from the bones2.
High phosphorus forces increased work for kidneys2.
The kidneys are also responsible for producing calitriol from vitamin D3.
Calitriol is needed for dietary calcium to be absorbed1.
If calitriol is low, PTH increases and calcium leaves the bones1.
Calitriol production decreases in CKD1.
Research shows vitamin D deficiency (23(OH)D concentration <15 ng/mL) in 86.8% of predialysis CKD patients1
Patients with parathyroid hyperplasia can display resistance to vitamin D action3.
CKD can decrease parathyroid vitamin D receptors5.
Vitamin D analogues (1a-calcidiol or doxecalciferol) and activators of vitamin D receptors (sVDRA: paricalcitol or mazacalcitol) mas help vitamin D levels5.
Potassium is also a concern because it can build up in the blood and result in hyperkalemia6.
Clinical Applications
Because CKD-MBD can cause irreversible damage and weakening of bones, prevention is imperative.
Recent studies show the primary method of prevention is through weight management and CKD maintenance9.
Diet interventions can decrease risk of CKD-MBD and CVD2.
Phosphorus can be decreased in the diet6 and Phosphate binders can be taken within minutes of eating to bind and remove excess phosphate from the body3.
Alert patients to potential phosphate in food additives and preservatives6.
Calcimimetrics are used with high PTH, calcium and phosphorus levels4.
Calcium supplements help to maintain balanced calcium levels along with increasing dietary sources10.
It must also be considered that dialysis may contain calcium4.
Calcium balance should be maintained because high levels of calcium in dialysis patients has show to increase mortality rates5.
With phosphate-protein ratio considered, foods high in protein tend to be high in phosphate. Consider adding milk, cheese, dried bean, peas, nuts, and peanut butter in the diet9.
Diagnostics
CKD-MBD is a systematic disorder4.
Classified with bone biopsy abnormalities, laboratory value abnormalities and soft-tissue/vascular abnormalities4.
The gold standard is bone biopsy-based histological analysis
Biopsy suggested when: unexplained fractures, persistent bone pain, unexplained hypercalcemia, unexplained hypophosphatemia, or possible aluminum toxicity
Serum phosphorus, calcium, and PTH can also be monitored with the goal of maintaining normal levels7.
Serum calcium should be at mg/dL and serum phosphorus should be at mg/dL8.
Serum alkaline phosphatase for bone turnover analysis7.