In a 79‑year‑old woman with elevated intact parathyroid hormone, normal calcium, serum creatinine 1.7 mg/dL and eGFR 29 mL/min, what is the diagnosis and how should it be managed?

Secondary Hyperparathyroidism Due to Chronic Kidney Disease

This 79-year-old woman has secondary hyperparathyroidism caused by CKD stage G3b (eGFR 29 mL/min/1.73 m²), and the first step is to evaluate for reversible causes—specifically vitamin D deficiency, hyperphosphatemia, and inadequate calcium intake—before considering any PTH-lowering therapy. 1, 2

Diagnosis

This patient's laboratory profile is diagnostic of CKD-related secondary hyperparathyroidism:

• PTH elevation begins when eGFR falls below 60 mL/min/1.73 m² and shows a significant inverse relationship with declining renal function 3
• Normal calcium excludes primary hyperparathyroidism, which typically presents with hypercalcemia and elevated or inappropriately normal PTH 2, 4
• At CKD stage G3b (eGFR 29), PTH levels of 132 pg/mL are expected as the kidneys lose their ability to excrete phosphate and produce active vitamin D 3, 5
• The intact PTH assay measures both active 1-84 PTH and inactive 7-84 fragments, with the inactive fragments accumulating disproportionately as kidney function declines 5

Initial Evaluation—Identify Reversible Causes

Before initiating any treatment, measure the following to exclude secondary causes that can be corrected 1, 6, 2:

1. 25-Hydroxyvitamin D Level

• Target ≥30 ng/mL to exclude vitamin D deficiency, the most common reversible cause of elevated PTH 6, 2
• If 25-OH vitamin D is <30 ng/mL, supplement with cholecalciferol or ergocalciferol to achieve levels ≥30 ng/mL before considering other interventions 6, 2
• Do NOT use calcitriol or active vitamin D analogs at this stage, as they increase hypercalcemia risk and can cause adynamic bone disease 1, 7

2. Serum Phosphorus

• Check for hyperphosphatemia, which drives PTH secretion in CKD 1, 6
• If phosphorus is elevated, restrict dietary phosphate intake as the first intervention 1, 6
• Consider phosphate binders only if dietary restriction fails to control phosphorus 1

3. Dietary Calcium Intake

• Assess whether the patient is consuming 1,000–1,200 mg of elemental calcium daily 6, 2, 8
• Inadequate calcium intake causes secondary hyperparathyroidism even with normal kidney function and vitamin D levels 8
• If intake is insufficient, supplement with calcium carbonate 600 mg twice daily and recheck PTH in 2–3 weeks 8

4. Medication Review

• Discontinue thiazide diuretics if present, as they reduce urinary calcium excretion and can worsen hyperparathyroidism 7
• Review for loop diuretics, bisphosphonates, or other medications affecting calcium metabolism 6

Management Algorithm

Step 1: Correct Modifiable Factors First 1, 2

1. Replete vitamin D to ≥30 ng/mL using cholecalciferol 1,000–2,000 IU daily 6, 2
2. Ensure adequate calcium intake (1,000–1,200 mg/day) through diet or supplementation 6, 8
3. Restrict dietary phosphate if hyperphosphatemia is present 1, 6
4. Recheck PTH after 3 months of correcting these factors 6, 2

Step 2: Reassess After Correction 1, 6

• If PTH normalizes or decreases significantly, continue monitoring calcium, phosphorus, and PTH every 3–6 months 1
• If PTH remains >110 pg/mL despite correction of vitamin D, calcium, and phosphorus, the patient has persistent secondary hyperparathyroidism requiring closer monitoring 1

Step 3: Avoid Routine Active Vitamin D Therapy 1

• Do NOT routinely prescribe calcitriol or vitamin D analogs in CKD G3b not on dialysis 1
• Reserve active vitamin D (calcitriol, alfacalcidol, doxercalciferol) only for severe and progressive hyperparathyroidism (PTH persistently >300 pg/mL with rising trend) in CKD G4–G5 1
• Active vitamin D increases hypercalcemia risk and can cause adynamic bone disease, especially in elderly patients 1, 7

Monitoring Schedule 1, 2

For CKD G3b (eGFR 29):

• Measure calcium and phosphorus every 3–6 months 1
• Measure PTH every 3–6 months after initial correction of reversible factors 1, 2
• During active treatment (if initiated), check calcium and phosphorus monthly for 3 months, then every 3 months 6, 2

Critical Pitfalls to Avoid

• Do not start calcitriol or active vitamin D analogs without first correcting vitamin D deficiency, calcium intake, and hyperphosphatemia 1, 2
• Do not target PTH suppression to normal range in CKD, as mild hyperparathyroidism may be protective against adynamic bone disease 1
• Do not use calcium-based phosphate binders if calcium is >10.2 mg/dL 4
• Recognize that PTH assays vary by up to 47% between platforms, so use assay-specific reference ranges and trend values over time 2, 4
• In elderly patients with age-related GFR decline, PTH elevation is expected and does not always require aggressive intervention 2