What is the diagnosis and management for a patient with hypercalcemia, hypernatremia, hyperkalemia, impaired renal function, and abnormal vitamin D levels, potentially indicating primary hyperparathyroidism?

Diagnosis: Primary Hyperparathyroidism with Vitamin D Deficiency and Iatrogenic Hypercalcemia

This patient has primary hyperparathyroidism (PHPT) complicated by vitamin D supplementation causing iatrogenic worsening of hypercalcemia, presenting with impaired renal function (eGFR 57) and meets surgical criteria.

Immediate Management Actions

Discontinue all vitamin D supplementation immediately, as serum calcium exceeds 10.2 mg/dL (patient has 10.4-11.0 mg/dL), which is the threshold for stopping vitamin D therapy in patients with impaired calcium regulation 1. The vitamin D level of 32 ng/mL is actually adequate (normal range 30-100 ng/mL), making supplementation unnecessary and potentially harmful 1.

Critical First Steps

• Stop all calcium-containing supplements and medications including calcium carbonate, calcium-based phosphate binders, thiazide diuretics, and any vitamin D preparations 1, 2.
• Ensure adequate oral hydration (2-3 liters daily if no contraindications) to promote calciuresis and prevent further renal injury 1, 3.
• Recheck serum calcium in 2-4 weeks after discontinuing vitamin D to determine if supplementation was the primary driver of worsening hypercalcemia 1.

Biochemical Diagnosis Confirmation

The laboratory pattern definitively confirms primary hyperparathyroidism:

• Hypercalcemia: Calcium 10.4-11.0 mg/dL (normal 8.7-10.3 mg/dL), with ionized calcium 5.5 mg/dL at upper limit of normal (4.5-5.6 mg/dL) 1.
• Elevated or inappropriately normal PTH: The PTH result shows "REFERT" status with interpretation table indicating primary hyperparathyroidism when PTH >65 pg/mL with calcium >10.2 mg/dL 4, 1.
• Low-normal phosphorus: 4.2 mg/dL (normal 3.0-4.3 mg/dL), characteristic of PHPT where PTH increases renal phosphate excretion 1.
• Impaired renal function: eGFR 57 mL/min/1.73m² (<60), which is an absolute surgical indication even with mild hypercalcemia 1.

Surgical Referral Criteria Met

This patient meets multiple criteria for parathyroidectomy and should be referred to an experienced parathyroid surgeon and endocrinology 4, 1:

• eGFR <60 mL/min/1.73m² (patient has eGFR 57) - this alone is an absolute indication regardless of calcium level 1.
• Corrected calcium >1 mg/dL above upper limit of normal - patient has calcium 10.4-11.0 mg/dL, which is 0.1-0.7 mg/dL above the upper limit of 10.3 mg/dL 1.
• Chronic hypercalcemia - multiple elevated values documented over time 4.

Preoperative Localization Imaging

• Order ultrasound and 99mTc-sestamibi scintigraphy with SPECT/CT for preoperative localization once biochemical diagnosis is confirmed and surgery is planned 1.
• Do not order parathyroid imaging before confirming biochemical diagnosis - imaging is for surgical planning only, not diagnosis 1.
• 4-D parathyroid CT (noncontrast, arterial, and venous phases) may be considered if ultrasound and sestamibi are discordant or non-localizing 4.

Management of Renal Impairment

The combination of hypercalcemia and CKD stage G3b requires careful monitoring:

• Hypercalcemia directly causes acute kidney injury and can worsen chronic kidney disease through nephrocalcinosis and calcium-phosphate deposition 1.
• Monitor serum calcium every 3 months for patients with CKD stage G3 and confirmed PHPT who are not immediate surgical candidates 1.
• Reassess renal function regularly (creatinine, eGFR) as hypercalcemia resolution after parathyroidectomy may improve kidney function 1.

Addressing the Vitamin D Paradox

The patient has adequate vitamin D (32 ng/mL) but was likely supplemented due to misinterpretation:

• Vitamin D deficiency (<30 ng/mL) can cause secondary hyperparathyroidism, but this patient has PRIMARY hyperparathyroidism with adequate vitamin D 1, 5.
• In PHPT, vitamin D supplementation is safe when calcium is normal, but must be stopped when calcium exceeds 10.2 mg/dL 1, 5.
• After calcium normalizes post-surgery, vitamin D can be cautiously restarted at low dose (800-1000 IU daily) with monthly calcium monitoring if deficiency develops 1.

Electrolyte Abnormalities Requiring Attention

Hyperkalemia (5.7 mmol/L, later 4.1 mmol/L)

• The initial hyperkalemia (5.7 mmol/L) resolved to normal (4.1 mmol/L), suggesting pseudohyperkalemia from hemolysis or delayed processing rather than true hyperkalemia 4.
• Recheck potassium if elevated to exclude laboratory artifact before treatment.

Low Bicarbonate (18 mmol/L)

• Metabolic acidosis (CO2 18 mmol/L) is unusual in PHPT, which typically causes hyperchloremic metabolic acidosis with normal or high bicarbonate 3.
• This may represent concurrent renal tubular acidosis from chronic hypercalcemia-induced renal injury or separate pathology requiring evaluation 3.
• Check arterial blood gas and urine pH if acidosis persists to characterize the acid-base disorder.

Monitoring Schedule Post-Intervention

• Measure serum calcium 2-4 weeks after stopping vitamin D to assess response 1.
• If calcium remains elevated, proceed with surgical evaluation without delay given eGFR <60 1.
• Monitor calcium and phosphorus monthly for first 3 months if surgery is delayed 1.
• Recheck 25-hydroxyvitamin D annually after parathyroidectomy to guide future supplementation 6.

Common Pitfalls to Avoid

• Never supplement vitamin D when calcium exceeds 10.2 mg/dL - this worsens hypercalcemia by increasing intestinal calcium absorption 1.
• Do not delay surgical referral in patients with eGFR <60 mL/min/1.73m², as this is an absolute indication regardless of symptom severity 1.
• Avoid calcium-based phosphate binders if patient has CKD and hypercalcemia, as these worsen calcium-phosphate product 1.
• Do not use calcitriol or vitamin D analogues in CKD G3a-G5 not on dialysis except for severe progressive hyperparathyroidism in CKD G4-G5 4.
• Never correct "low" PTH to normal range in dialysis patients if surgery is delayed, as this causes adynamic bone disease 6.

Expected Outcomes After Parathyroidectomy

• Normalization of calcium within 6 months defines successful surgery; failure indicates persistent PHPT requiring reimaging 4.
• Improvement in eGFR may occur if hypercalcemia-induced renal injury is reversible 1.
• Risk of hungry bone syndrome with severe hypocalcemia post-operatively requires aggressive calcium and vitamin D supplementation immediately after surgery 6.