How to manage a patient with kidney stones and elevated alkaline phosphatase?

Management of Patients with Kidney Stones and Elevated Alkaline Phosphatase

Patients with kidney stones and elevated alkaline phosphatase should undergo bone scan evaluation if they have bone pain or radiographic findings suggestive of bone metastases, as elevated alkaline phosphatase may indicate bone involvement or metastatic disease. 1

Diagnostic Approach

When managing a patient with kidney stones and elevated alkaline phosphatase (ALP), a systematic evaluation is necessary to determine the underlying cause:

1. Rule out metastatic disease:

   • Bone scan is indicated when elevated alkaline phosphatase is present, especially with bone pain or radiographic findings suggesting bone neoplasm 1
   • Without symptoms of bone pain or elevated ALP, the yield of bone scan is low, but with these findings, the incidence of metastatic disease can be up to 10% 1

2. Laboratory evaluation:

   • Complete metabolic panel including calcium, phosphorus, PTH levels 1
   • Urinalysis and 24-hour urine collection for stone risk factors 1
   • Liver function tests to differentiate hepatic from bone sources of ALP 1
   • Consider ALP isoenzyme testing if source is unclear 2

3. Consider other causes of elevated ALP:

   • Bone involvement from malignancy or Paget's disease 3
   • Sepsis (can have extremely high ALP with normal bilirubin) 3
   • Biliary obstruction 3
   • Renal damage (ALP may be derived from injury to brush border membrane of renal tubular cells) 2
   • Left ventricular diastolic dysfunction in CKD patients 4

Management Algorithm

1. For Kidney Stone Management:

• Acute management:

  • Pain control
  • Hydration
  • Medical expulsive therapy if appropriate

• Preventive therapy based on stone type:

  • Calcium stones with hypocitraturia: Potassium citrate 20 mEq three times daily 5
  • Uric acid stones: Potassium citrate to raise urinary pH to 6.0 1
  • Cystine stones: Potassium citrate to raise urinary pH to 7.0 1

• Follow-up monitoring:

  • Obtain a 24-hour urine specimen within six months of initiating treatment 1
  • Annual 24-hour urine specimen thereafter or more frequently based on stone activity 1
  • Periodic blood testing to assess for adverse effects of pharmacological therapy 1

2. For Elevated Alkaline Phosphatase:

• If patient has CKD:

  • Monitor calcium, phosphorus, PTH, and alkaline phosphatase regularly based on CKD stage 1
  • For CKD stages 3a-5, measurement of alkaline phosphatases annually, or more frequently with elevated PTH 1
  • Consider bone biopsy in patients with biochemical abnormalities of CKD-MBD and low BMD/fragility fractures 1

• If bone involvement is suspected:

  • Bone scan if bone pain or radiographic findings suggest bone neoplasm 1
  • Consider referral to endocrinology or oncology based on findings

• If renal damage is suspected:

  • Complete removal of stones if present 2
  • Monitor ALP levels after treatment as they should return to normal range 2

Special Considerations

1. CKD patients with kidney stones:

   • Appropriate referral to nephrology to prevent further deterioration of renal function that can affect bone and metabolic health 1
   • In patients with CKD G3a-G5D, avoid hypercalcemia and maintain serum calcium in the age-appropriate normal range 1

2. Patients with hyperparathyroidism:

   • Consider parathyroidectomy for patients with persistent hypercalcemic hyperparathyroidism despite optimized therapy 1
   • For patients with severe hyperparathyroidism who fail to respond to medical therapy, parathyroidectomy may be indicated 1

3. Patients with X-linked hypophosphataemia (XLH):

   • Elevated ALP may indicate inadequate treatment 1
   • Consider increasing the dose of active vitamin D or adjusting phosphate supplements 1

Common Pitfalls to Avoid

1. Don't assume all elevated ALP is bone-related:

   • Liver disease, sepsis, and other conditions can cause elevated ALP 3
   • Consider isoenzyme testing if the source is unclear

2. Don't miss metastatic disease:

   • Elevated ALP with bone pain warrants bone scan evaluation 1
   • The incidence of metastatic disease is significant (up to 10%) when suspicious musculoskeletal symptoms are present with elevated ALP 1

3. Don't overlook the connection between kidney and bone health:

   • Renal function impairment may be responsible for increased serum ALP 2
   • Serum ALP may be a marker for kidney involvement in pathological processes 2

4. Don't forget to monitor for treatment efficacy:

   • Follow-up 24-hour urine collections are essential to assess response to therapy 1
   • ALP levels should normalize with appropriate treatment of the underlying condition 2

By following this structured approach, clinicians can effectively manage patients with kidney stones and elevated alkaline phosphatase, addressing both conditions while monitoring for potential serious underlying causes.