Mineral and Bone Disorder (CKD-MBD)
Disturbed calcium, phosphorus, and bone health in kidney disease
Quick Facts
- Type: Complication of chronic kidney disease
- Minerals involved: Calcium, phosphorus, vitamin D
- Key hormone: Parathyroid hormone (PTH)
- Main effects: Weak bones, blood vessel calcification
Overview
Mineral and bone disorder, often called CKD-MBD (chronic kidney disease–mineral and bone disorder), is a group of problems that develop when the kidneys can no longer properly manage the minerals calcium and phosphorus and the activation of vitamin D. Healthy kidneys help keep these in balance and activate vitamin D, which is needed for strong bones. As kidney function declines, this balance is disrupted.
The result can be weakened or abnormal bones, high parathyroid hormone levels, and deposits of calcium in blood vessels and soft tissues. CKD-MBD is an important complication of chronic kidney disease because it raises the risk of fractures and contributes to heart and blood vessel disease.
Symptoms
Early on, there are often no symptoms, and the disorder is detected through blood tests. As it progresses, symptoms may include:
- Bone or joint pain
- Muscle weakness
- Itching of the skin
- Increased risk of bone fractures
- Bone deformities, especially in children
Because much of the damage happens silently, monitoring blood levels of calcium, phosphorus, parathyroid hormone, and vitamin D is essential in people with chronic kidney disease, even before symptoms appear.
Causes
CKD-MBD develops because failing kidneys disrupt several interconnected processes:
- Phosphorus buildup: Damaged kidneys cannot remove excess phosphorus, so it accumulates in the blood.
- Low active vitamin D: The kidneys normally activate vitamin D; reduced function lowers calcium absorption from food.
- Low or abnormal calcium: Resulting from reduced vitamin D activation and high phosphorus.
- Overactive parathyroid glands: These glands release more parathyroid hormone (PTH) to compensate, which pulls calcium from bones and weakens them.
Over time these changes harm the bones and lead to calcium deposits in blood vessels.
Risk Factors
- Chronic kidney disease, with risk rising as kidney function falls
- Being on dialysis
- Long-standing or poorly controlled kidney disease
- Diabetes and high blood pressure (common causes of kidney disease)
- Vitamin D deficiency
Diagnosis
Diagnosis relies mainly on blood tests that track calcium, phosphorus, parathyroid hormone (PTH), and vitamin D levels over time in people with chronic kidney disease. Trends in these values help guide treatment.
Imaging such as X-rays may show bone changes or blood vessel calcification. In selected cases, a bone density scan or, rarely, a bone biopsy may be used to clarify the type of bone disease present.
Treatment
Treatment aims to restore balance of calcium and phosphorus, control parathyroid hormone, and protect the bones and blood vessels:
- Dietary phosphorus control: Limiting high-phosphorus foods, often with guidance from a kidney dietitian.
- Phosphate binders: Medications taken with meals to reduce phosphorus absorption.
- Vitamin D and active vitamin D analogs: To support calcium balance and lower parathyroid hormone.
- Medications to lower PTH: Such as calcimimetics in selected patients.
- Managing the underlying kidney disease: Including dialysis adjustments when needed.
- Parathyroid surgery: Occasionally needed if the parathyroid glands become severely overactive.
Prevention
- Manage chronic kidney disease and its causes, such as diabetes and high blood pressure
- Follow recommended dietary phosphorus limits
- Take phosphate binders and other prescribed medications as directed
- Keep regular appointments for blood test monitoring
- Maintain adequate vitamin D as advised by your care team
When to See a Doctor
If you have chronic kidney disease, keep regular follow-up so that mineral and bone problems can be detected early through blood tests. Tell your care team about new bone or joint pain, muscle weakness, or persistent itching.
Seek prompt medical care for a fracture after a minor injury, severe bone pain, or symptoms of dangerously abnormal calcium such as confusion, severe muscle weakness, or an irregular heartbeat. These need timely evaluation.
Frequently Asked Questions
What is CKD-MBD?
CKD-MBD stands for chronic kidney disease–mineral and bone disorder. It describes the disturbances in calcium, phosphorus, vitamin D, and parathyroid hormone, and the resulting bone and blood vessel problems, that develop as a complication of chronic kidney disease.
Why does kidney disease affect the bones?
Healthy kidneys help balance calcium and phosphorus and activate vitamin D, all of which are needed for strong bones. When kidneys fail, phosphorus builds up, active vitamin D falls, and parathyroid hormone rises, pulling calcium from bones and weakening them.
Can mineral and bone disorder be treated?
Yes. Treatment includes limiting dietary phosphorus, taking phosphate binders, using vitamin D and medications to control parathyroid hormone, and managing the underlying kidney disease. Regular blood monitoring guides the plan.
Does it cause symptoms early?
Often not. Early CKD-MBD is usually silent and detected only through blood tests, which is why people with chronic kidney disease are monitored regularly. Bone pain, weakness, and fractures tend to appear later.
What dietary changes help?
Limiting high-phosphorus foods is central, ideally with guidance from a kidney dietitian. Taking phosphate binders with meals and maintaining adequate vitamin D as advised also help keep minerals in balance.
References
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Mineral & Bone Disorder in Chronic Kidney Disease.
- National Kidney Foundation.
- MedlinePlus, U.S. National Library of Medicine. Chronic kidney disease.
- Kidney Disease: Improving Global Outcomes (KDIGO).