Chronic Kidney Disease–Mineral and Bone Disorder (CKD–MBD)

Chronic Kidney Disease–Mineral and Bone Disorder (CKD–MBD) is a systemic disorder of mineral and bone metabolism that develops as kidney function progressively declines. It is characterized by abnormalities in calcium, phosphate, parathyroid hormone (PTH), and vitamin D metabolism, resulting in bone disease, extraskeletal calcification, and increased cardiovascular morbidity and mortality.

CKD–MBD is common among patients with advanced chronic kidney disease, particularly those receiving maintenance haemodialysis. Early detection and appropriate management are essential to reduce fractures, improve bone health, minimize vascular calcification, and decrease cardiovascular complications.

Epidemiology

CKD–MBD affects a large proportion of patients with CKD Stages 3–5, with prevalence increasing as kidney function deteriorates. Secondary hyperparathyroidism, hyperphosphataemia, hypocalcaemia, and vitamin D deficiency become progressively more common in advanced CKD. Patients receiving dialysis are at particularly high risk of severe mineral and bone abnormalities, vascular calcification, cardiovascular disease, and premature mortality.

Risk factors

Common risk factors include:

• Chronic Kidney Disease (Stages 3–5)

• End-stage kidney disease

• Long-term haemodialysis or peritoneal dialysis

• Hyperphosphataemia

• Hypocalcaemia

• Vitamin D deficiency

• Secondary hyperparathyroidism

• Poor dietary adherence

• Diabetes mellitus

• Advanced age

• Previous fragility fractures

Pathophysiology

Healthy kidneys regulate calcium, phosphate, vitamin D metabolism, and parathyroid hormone secretion. Progressive decline in kidney function reduces phosphate excretion and impairs activation of vitamin D, resulting in phosphate retention, hypocalcaemia, and reduced intestinal calcium absorption.

These abnormalities stimulate increased secretion of parathyroid hormone (secondary hyperparathyroidism), leading to increased bone turnover, bone demineralization, skeletal deformities, and fractures. Persistent disturbances in mineral metabolism also promote vascular and soft tissue calcification, contributing significantly to cardiovascular disease and mortality.

Clinical presentation

Clinical manifestations usually occur in advanced CKD.

Patients may present with:

• Bone pain

• Generalized muscle weakness

• Bone tenderness

• Skeletal deformities

• Fragility fractures

• Convulsions

• Tetany

• Joint pain

• Pruritus

• Symptoms of chronic kidney disease

Clinical signs may include:

• Bone tenderness

• Skeletal deformities

• Soft tissue or vascular calcification

• Fractures

• Neuromuscular irritability associated with hypocalcaemia

• Features of advanced chronic kidney disease

Diagnostic criteria

CKD–MBD should be suspected in patients with CKD Stage 3 or higher who have one or more of the following:

• Abnormal serum calcium.

• Hyperphosphataemia.

• Elevated parathyroid hormone levels.

• Vitamin D deficiency.

• Evidence of renal bone disease.

• Extraskeletal or vascular calcification.

Diagnosis is based on biochemical abnormalities together with clinical and radiological findings.

Investigations

Patients with CKD Stage 3 or higher should undergo evaluation for CKD–MBD.

Recommended investigations include:

Biochemical investigations

• Serum calcium.

• Serum albumin (for corrected calcium calculation).

• Serum phosphate.

• Intact parathyroid hormone (PTH).

• Serum vitamin D level.

• Serum alkaline phosphatase where available.

Imaging

• Lateral lumbar spine X-ray.

• Dual-energy X-ray absorptiometry (DEXA) scan in patients suspected of osteoporosis or those at increased fracture risk.

Additional investigations should be guided by the patient's clinical condition.

Management

Management aims to:

• Correct abnormalities of calcium and phosphate metabolism.

• Control secondary hyperparathyroidism.

• Prevent fractures.

• Reduce vascular and soft tissue calcification.

• Reduce cardiovascular complications.

• Improve quality of life.

Non-pharmacological treatment

General measures include:

• Provide nutritional counselling.

• Restrict dietary phosphate intake.

• Encourage adequate dietary calcium intake where appropriate.

• Avoid excessive dietary phosphate additives.

• Optimize management of chronic kidney disease.

• Encourage adherence to prescribed medications.

• Monitor calcium, phosphate, and parathyroid hormone levels regularly.

Pharmacological treatment

Management of hyperphosphataemia

Patients with hyperphosphataemia, particularly those with associated hypocalcaemia, should receive phosphate-binding therapy.

Recommended treatment:

• Calcium carbonate 500–1500 mg orally every 8 hours with meals.

Treatment should be individualized according to serum phosphate and corrected calcium concentrations.

Persistent hyperphosphataemia or severe secondary hyperparathyroidism should be managed in consultation with a nephrologist. Additional therapies, including non-calcium phosphate binders, vitamin D analogues, or calcimimetic agents, may be required according to specialist recommendations.

Referral

Refer patients to a nephrologist when:

• Persistent hyperphosphataemia despite treatment.

• Severe secondary hyperparathyroidism.

• Recurrent hypocalcaemia.

• Pathological fractures.

• Progressive vascular or soft tissue calcification.

• CKD Stage 4 or Stage 5.

• Patients receiving dialysis who require specialized management of CKD–MBD.

Complications

Potential complications include:

• Renal osteodystrophy.

• Secondary hyperparathyroidism.

• Fragility fractures.

• Osteoporosis.

• Bone deformities.

• Vascular calcification.

• Soft tissue calcification.

• Calciphylaxis.

• Cardiovascular disease.

• Increased mortality.

Prognosis

The prognosis depends on the severity of chronic kidney disease, degree of mineral metabolism abnormalities, cardiovascular involvement, and response to treatment. Early identification and correction of calcium, phosphate, vitamin D, and parathyroid hormone abnormalities can reduce fracture risk, improve bone health, slow progression of secondary hyperparathyroidism, and decrease cardiovascular morbidity and mortality.

Prevention

Preventive measures include:

• Early detection and management of chronic kidney disease.

• Routine monitoring of calcium, phosphate, and parathyroid hormone in patients with CKD Stage 3 or higher.

• Early treatment of hyperphosphataemia.

• Appropriate dietary phosphate restriction.

• Adequate calcium intake where indicated.

• Correction of vitamin D deficiency.

• Regular assessment of bone health in high-risk patients.

• Early referral to nephrology services for advanced CKD.