CKD mineral and bone disorder

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

As nephron mass falls, phosphate retention and fibroblast growth factor 23 reduce active vitamin-D availability. Calcium absorption falls and the parathyroid glands increase hormone secretion. This compensatory system may preserve serum values early, so normal phosphate does not prove normal bone physiology. Persistent stimulation can progress to gland hyperplasia, very high turnover, bone pain and fracture, while treatment excess can suppress turnover too far.

The vascular component matters. Positive calcium and phosphate balance contributes to arterial and valvular calcification, particularly when calcium-based binders, active vitamin D and dialysate calcium are layered without reviewing the whole profile. Treatment therefore seeks acceptable trends rather than normalising PTH at any cost, and the safest binder differs with calcium, PTH, calcification, iron status, bowel tolerance and pill burden.

Fracture assessment remains clinical. DXA can estimate fracture risk, but it does not define turnover; alkaline phosphatase, PTH trajectory, imaging and occasionally bone biopsy add phenotype information. An individual with G4 CKD and a fragility fracture deserves renal and osteoporosis expertise because bisphosphonate, denosumab and anabolic choices have renal, calcium and turnover-specific risks.

Key points

CKD-MBD links disordered phosphate, calcium, vitamin-D and parathyroid physiology with renal osteodystrophy, fracture and vascular or soft-tissue calcification; it is more than an isolated high phosphate.
Falling phosphate excretion and reduced calcitriol drive secondary hyperparathyroidism, initially maintaining serum calcium and phosphate at the cost of high bone turnover.
Interpret serial calcium, phosphate, alkaline phosphatase and PTH together; a single modest PTH elevation can be adaptive and should not trigger automatic active-vitamin-D treatment.
Before treating rising PTH, correct modifiable high phosphate intake, hyperphosphataemia, hypocalcaemia and native vitamin-D deficiency and review adherence to dialysis and binders.
Dietary phosphate advice should focus on highly bioavailable additives and excessive intake while preserving protein and energy; specialist renal dietitians prevent harmful blanket restriction.
Phosphate binders work only when taken with phosphate-containing food. NICE starts adults with stage 4–5 hyperphosphataemia on calcium acetate, then individualises alternatives; UKKA advises limiting calcium loading.
Do not use binders pre-emptively for normal phosphate solely to suppress PTH, and do not judge success without checking meal timing, tablet burden and constipation.
Active vitamin-D analogues are not routine in non-dialysis CKD; reserve them for severe progressive secondary hyperparathyroidism under renal supervision while avoiding hypercalcaemia and hyperphosphataemia.
Calcimimetics are specialist therapies for selected dialysis-associated secondary hyperparathyroidism and can cause clinically important hypocalcaemia; cinacalcet is not indicated for predialysis CKD.
Bone pain or fracture in CKD needs a differential including osteoporosis, osteomalacia, high- or low-turnover renal bone disease, malignancy and aluminium exposure; indiscriminate antiresorptive therapy can be unsafe.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Reduced kidney function

Declining phosphate excretion and impaired vitamin-D activation initiate the linked mineral and hormonal disturbance, becoming more clinically important as chronic kidney disease advances.

Sustained secondary hyperparathyroidism

Persistent phosphate burden, low calcitriol and hypocalcaemic signalling drive parathyroid hyperplasia and increasingly autonomous hormone production over time.

Treatment and nutritional modifiers

Dietary phosphate additives, inadequate dialysis, binder timing, excessive calcium loading and vitamin-D therapies can worsen or reshape the biochemical and skeletal phenotype.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Phosphate retention signalling
Falling nephron mass reduces phosphate clearance and increases phosphaturic hormonal signalling, initially keeping serum phosphate deceptively stable.
2
Calcitriol and calcium decline
Reduced renal calcitriol synthesis limits intestinal calcium absorption, while phosphate retention further lowers ionised calcium and stimulates parathyroid secretion.
3
Abnormal bone turnover
Chronic PTH excess accelerates bone resorption, whereas oversuppression or other factors can produce low-turnover bone; both weaken skeletal quality.
4
Extra-skeletal calcification
Persistent mineral imbalance and calcium loading favour vascular and soft-tissue mineral deposition, contributing to arterial stiffness and cardiovascular disease.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Biochemical evolution

Rising PTH and alkaline phosphatase may precede overt hyperphosphataemia or hypocalcaemia as compensatory secondary hyperparathyroidism develops.

High-turnover disease

Bone pain, proximal weakness, fracture and markedly rising PTH or alkaline phosphatase can reflect osteitis fibrosa, although biochemical and skeletal differentials remain.

Low-turnover risk

Low or falling PTH after heavy calcium, active vitamin-D or calcimimetic exposure can indicate oversuppression and adynamic bone vulnerability.

Calcification phenotype

Arterial stiffness, valvular disease or radiological vascular and soft-tissue calcium deposition strengthens the reason to avoid unnecessary calcium loading.

Dietary burden

Processed foods with phosphate additives deliver readily absorbed phosphate, whereas removing all protein-rich food can precipitate protein-energy wasting.

Tertiary autonomy

Persistent high PTH with hypercalcaemia after prolonged secondary stimulation, including after transplantation, suggests autonomous gland function needing specialist treatment.

Red flags requiring action

Painful retiform skin lesions, livedoid change and necrosis in advanced CKD may represent calciphylaxis and require urgent renal, dermatology, wound, infection and analgesia care.
Symptomatic severe hypocalcaemia with tetany, seizure, laryngospasm or QT prolongation during calcimimetic therapy requires emergency calcium management and treatment review.
A pathological fracture, cord-compression symptoms or severe focal bone pain needs urgent imaging and assessment for malignancy, infection and structural instability rather than presumed renal bone disease.
Marked hypercalcaemia with confusion, dehydration or arrhythmia is not typical compensated secondary hyperparathyroidism and needs immediate cause-directed assessment.
Rapidly progressive severe hyperparathyroidism despite medicine may require parathyroidectomy planning; uncontrolled phosphate and calcimimetic or vitamin-D adverse effects should not be tolerated indefinitely.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Adjusted or ionised serum calciumFirst step
Why
Identify hypo- or hypercalcaemia and guide vitamin-D, binder and calcimimetic safety.
Interpretation and limitations
Albumin correction can be unreliable in severe illness; use ionised calcium when precision matters and interpret magnesium, acid-base status and recent dialysis.
02
Serum phosphate trend
Why
Measure retained phosphate and response to dietary, binder and dialysis interventions.
Interpretation and limitations
Use serial predialysis samples where applicable; rising or persistently high values prompt treatment, whereas a low value may indicate poor nutrition or excessive clearance.
03
Parathyroid hormone trend
Why
Assess compensatory activity and risk of high- or low-turnover bone disease.
Interpretation and limitations
Interpret direction, assay range, CKD stage, calcium, phosphate and alkaline phosphatase; treatment should not rest on one modest elevation.
04
Alkaline phosphatase and liver profile
Why
Provide an accessible turnover clue while distinguishing hepatic enzyme elevation.
Interpretation and limitations
A rising bone-derived component can support high turnover; normal results do not exclude fracture risk and very low turnover may occur with oversuppressed PTH.
05
25-hydroxyvitamin D
Why
Identify native vitamin-D deficiency as a modifiable driver of secondary hyperparathyroidism and osteomalacia.
Interpretation and limitations
Replace deficiency using current UK guidance and re-evaluate calcium, phosphate and PTH; this test is distinct from active calcitriol concentration.
06
DXA and vertebral fracture assessment
Why
Estimate fracture risk when results will change therapy or reveal occult vertebral damage.
Interpretation and limitations
Low density predicts fracture but cannot distinguish high from low turnover; combine with CKD-MBD biochemistry and specialist medicine selection.
07
Plain imaging or vascular imaging review
Why
Detect fracture, subperiosteal change and existing vascular or valvular calcification when clinically relevant.
Interpretation and limitations
Calcification supports limiting calcium burden but is not a stand-alone indication for a specific binder; focal lesions need a broader differential.
08
Bone biopsy
Why
Define turnover, mineralisation and volume when uncertainty would materially alter a high-risk treatment.
Interpretation and limitations
This is a specialist test, considered before potentially harmful antiresorptive or anabolic therapy when non-invasive evidence cannot distinguish renal bone phenotypes.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Primary hyperparathyroidism

Hypercalcaemia with inappropriately raised PTH suggests autonomous primary gland disease, whereas CKD-related secondary disease more often develops with phosphate and calcitriol disturbance.

Nutritional vitamin-D deficiency

Low native vitamin-D can elevate PTH and cause osteomalacia independently or alongside CKD; the wider calcium, phosphate and renal trajectory clarifies contribution.

Age-related osteoporosis

Fragility fracture with normal CKD mineral trends may reflect osteoporosis, while renal osteodystrophy requires integrated biochemical and sometimes bone-turnover assessment.

Malignancy or other metabolic bone disease

Focal pain, disproportionate alkaline phosphatase, anaemia or atypical calcium disturbance should prompt evaluation beyond CKD-MBD rather than automatic binder or PTH treatment.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01PROFILEAbnormal CKD-MBD bloodsFirst stepPhosphate, calcium, PTH or alkaline phosphatase changes in moderate or advanced CKD.

1Repeat and trend the linked profile, checking CKD trajectory, dialysis timing, albumin, magnesium, liver source and all binders, supplements and vitamin-D products.
2Identify modifiable phosphate intake, vitamin-D deficiency, hypocalcaemia, dialysis inadequacy, non-adherence and treatment oversuppression.
3Treat the pattern rather than one result, setting a renal-service monitoring interval and avoiding simultaneous untracked changes to several agents.
4EscalationEscalate severe symptoms, calciphylaxis, fracture or refractory hyperparathyroidism to the relevant urgent multidisciplinary pathway.

02PHOSPHATEPersistent hyperphosphataemiaSerum phosphate remains raised in stage 4–5 CKD or dialysis after confirmation.

1Ask a renal dietitian to identify phosphate additives and high-load foods while preserving adequate protein, energy and cultural acceptability.
2Review dialysis adequacy and residual function, then choose a binder using NICE sequencing plus calcium, PTH, calcification, bowel function, iron and pill burden.
3Teach the patient to take the binder with phosphate-containing meals or snacks and adapt the dose distribution to what they actually eat.
4EscalationRecheck phosphate, calcium, PTH, tolerance and adherence before escalating; do not prescribe tablets as a substitute for an ineffective dialysis prescription.

03PTHProgressive secondary hyperparathyroidismPTH rises persistently or markedly with a compatible CKD-MBD profile.

1Correct native vitamin-D deficiency, high phosphate intake, hyperphosphataemia and hypocalcaemia and review treatment adherence and dialysis delivery.
2In non-dialysis G4–G5, reserve active vitamin-D analogue for severe progressive disease under nephrology rather than treating every mild rise.
3In dialysis, select active vitamin D, a calcimimetic or combination from calcium, phosphate, PTH trajectory, comorbidity and current commissioning criteria.
4Discuss parathyroidectomy when severe disease remains uncontrolled, planning perioperative hungry-bone calcium management in advance.

04FRACTUREFragility fracture or low bone densityA person with CKD has a low-trauma fracture, vertebral deformity or high calculated fracture risk.

1Exclude malignancy, myeloma, infection and osteomalacia and obtain calcium, phosphate, PTH, alkaline phosphatase, vitamin D and relevant imaging.
2Determine whether CKD-MBD is biochemically important and whether turnover uncertainty warrants bone or metabolic-bone specialist review.
3Choose osteoporosis therapy using renal-stage licensing, calcium balance and turnover risk; arrange dental and hypocalcaemia safeguards for the selected drug.
4Add falls, strength, vision, nutrition, smoking and home-safety measures and monitor fracture outcomes rather than DXA alone.

Key medicines and prescribing safety5 treatments · regimens, roles and cautions

Bind dietary phosphate in the gut as NICE's first offered adult option when a calcium-containing binder is appropriate.

Calcium acetate

Use the BNF meal-linked starting regimen for stage 4 or 5 CKD hyperphosphataemia and titrate to phosphate response and calcium burden.

Take with food; monitor hypercalcaemia, constipation, PTH oversuppression and vascular calcification and avoid uncritical cumulative calcium from supplements or dialysate.

Provide a non-calcium phosphate binder when NICE circumstances, calcium load or intolerance make it preferable.

Sevelamer carbonate

Use the current SmPC meal-divided dose selected from phosphate concentration and titrate at the licensed interval under the renal formulary.

Large tablet burden, nausea, constipation, bowel obstruction risk and binding of other medicines reduce safety and adherence; check product timing and fat-soluble vitamin context.

Correct a common modifiable cause of secondary hyperparathyroidism and osteomalacia risk.

Native vitamin D

Replace confirmed deficiency with the current colecalciferol or ergocalciferol regimen, then use an individual maintenance plan and repeat the linked mineral profile.

Do not confuse native replacement with routine active-vitamin-D therapy; monitor calcium and phosphate and avoid cumulative over-the-counter duplication.

Suppress parathyroid drive when correction of modifiable factors is insufficient in selected advanced CKD or dialysis.

Active vitamin-D analogue

Use calcitriol or alfacalcidol only in the specialist regimen for severe progressive secondary hyperparathyroidism, titrated against calcium, phosphate and PTH.

Hypercalcaemia, hyperphosphataemia, calcification and adynamic bone can result; non-dialysis routine use is not recommended and the products are not dose-equivalent.

Increase calcium-sensing-receptor sensitivity and lower PTH when standard measures are inadequate or a calcimimetic profile is favoured.

Cinacalcet

For selected maintenance-dialysis secondary hyperparathyroidism, use the current SmPC oral starting and titration schedule within NICE and local specialist criteria.

Not indicated for non-dialysis CKD; nausea and hypocalcaemia are important, calcium must be checked soon after changes, and severe low calcium can lower seizure threshold or prolong QT.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Fracture and skeletal pain

High-turnover, low-turnover or mineralisation defects reduce bone strength, causing fragility fracture, bone pain, weakness and impaired mobility.

Vascular calcification

Calcium-phosphate deposition stiffens arteries and valves, increasing pulse pressure and adding to the already high cardiovascular burden of CKD.

Severe hyperparathyroidism

Progressive gland hyperplasia can become difficult to suppress, sustaining pruritus, bone turnover and mineral release despite correction of initial drivers.

Treatment-related mineral injury

Excess calcium, active vitamin-D or calcimimetic effect can produce hypercalcaemia, hyperphosphataemia or hypocalcaemia and may worsen calcification or symptoms.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Trend calcium, phosphate, PTH and alkaline phosphatase at intervals determined by CKD stage, abnormality magnitude, dialysis modality and treatment changes rather than ordering isolated unsynchronised tests.
After starting or changing a binder, review phosphate, calcium, gastrointestinal tolerance, meal timing and tablet burden; biochemical failure often reflects how it is taken.
Measure calcium promptly after calcimimetic initiation or adjustment and reassess symptoms such as paraesthesia, cramp, seizure or cardiac instability.
During active vitamin-D therapy, watch calcium and phosphate closely and reduce exposure before persistent hypercalcaemia, hyperphosphataemia or PTH oversuppression develops.
Review dietary intake with a renal dietitian, including additive labels, protein adequacy and weight trajectory; low phosphate from malnutrition is not therapeutic success.
Track fracture, bone pain, mobility, falls and height or vertebral symptoms, because biochemical control does not guarantee skeletal protection.
Reconsider parathyroid surgery when medical burden rises without control and monitor intensively for postoperative hungry-bone hypocalcaemia.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Normal phosphate can be costly

Early CKD may maintain serum phosphate through FGF23 and PTH elevation, transferring the burden to bone and endocrine physiology.

PTH is a trend signal

A modest isolated rise may be adaptive; serial direction and the calcium-phosphate context are more useful than one assay value.

Binders need a meal

A perfectly selected binder taken at bedtime without food cannot intercept the phosphate absorbed from lunch and dinner.

Additives are highly available

Inorganic phosphate added to processed food is absorbed more readily than plant phytate, allowing targeted advice with less nutritional harm.

DXA cannot show turnover

Bone density predicts fracture but does not reveal whether renal bone is high-turnover, adynamic or poorly mineralised.

Too little PTH can also harm

Heavy calcium, vitamin-D and calcimimetic exposure may suppress remodelling and create adynamic bone despite apparently excellent laboratory control.

11Common pitfallsFrequent interpretation and management errors.

01
Do not diagnose or treat CKD-MBD from one PTH value without calcium, phosphate, alkaline phosphatase, stage and trend.
02
Do not prescribe a phosphate binder without teaching meal-linked dosing and checking whether tablet burden is feasible.
03
Do not restrict all protein-rich foods to lower phosphate and inadvertently cause protein-energy wasting.
04
Do not use active vitamin D routinely for mild PTH elevation in non-dialysis CKD before correcting modifiable factors.
05
Do not give cinacalcet for predialysis CKD or ignore treatment-associated hypocalcaemia.
06
Do not assume every fragility fracture in CKD has the same turnover phenotype or start an antiresorptive without renal-stage safeguards.
07
Do not overlook calciphylaxis when painful skin lesions appear in advanced CKD; delay worsens infection, pain and mortality.