What tests should be ordered every 3 to 6 months for a patient with CKD stage 4, hyperphosphatemia, and early changes in bone metabolism: serum PTH or 25-hydroxy Vitamin D?

From the Guidelines

Test Ordering for CKD Stage 4 Patients

For a patient with CKD stage 4, hyperphosphatemia, and early changes in bone metabolism, serum PTH should be ordered every 6-12 months, as per the guidelines 1.

Rationale and Evidence

The KDIGO guideline update from 2017 recommends monitoring serum levels of calcium, phosphate, PTH, and alkaline phosphatase activity in patients with CKD G3a-G5D 1. Specifically, for CKD G4 patients, it suggests monitoring serum calcium and phosphate every 3-6 months and PTH every 6-12 months. The K/DOQI clinical practice guidelines from 2003 also support the measurement of plasma intact PTH in CKD patients, especially when plasma intact PTH is above the target range for the stage of CKD 1.

Additional Recommendations

In addition to PTH, serum 25-hydroxy Vitamin D should be measured at the first encounter if plasma intact PTH is above the target range, and if the level of 25-hydroxy Vitamin D is <30 ng/mL, supplementation with vitamin D2 should be initiated 1. The guidelines also recommend monitoring serum levels of corrected total calcium and phosphorus at least every 3 months following initiation of vitamin D therapy 1.

Monitoring Intervals

The monitoring intervals for these tests may vary depending on the presence and magnitude of abnormalities and the rate of progression of CKD 1. However, for CKD G4 patients with hyperphosphatemia and early changes in bone metabolism, ordering serum PTH every 6-12 months and serum calcium and phosphate every 3-6 months is a reasonable approach, as per the guidelines 1.

From the Research

Tests for CKD Stage 4 Patients

For a patient with CKD stage 4, hyperphosphatemia, and early changes in bone metabolism, regular monitoring of certain parameters is crucial. The tests that should be ordered every 3 to 6 months include:

• Serum PTH (Parathyroid Hormone) levels: According to 2, PTH values of 1.7-5 times the upper normal limit (ULN) may be optimal in patients with CKD stage 4. Monitoring PTH levels helps in assessing the severity of secondary hyperparathyroidism and guiding treatment decisions.
• 25-hydroxy Vitamin D levels: As suggested by 3, maintaining adequate levels of 25-hydroxy Vitamin D (> 30 ng/mL) is essential, and levels should be checked every 6-12 months. This helps in preventing deficiency and related complications.
• Serum calcium and phosphorus levels: Regular measurement of these parameters is crucial for therapeutic management, especially during dose titration stages of intestinal phosphorus binders, vitamin D analogs, or calcimimetics 4.
• Other markers of bone turnover, such as osteocalcin, total and bone alkaline phosphate, free pyridolines in serum, and C-terminal telopeptide of collagen, may not be necessary for routine monitoring, as they do not improve the predictive power of PTH 4.

Frequency of Testing

The frequency of testing may vary depending on the individual patient's condition and treatment response. However, as a general guideline, the following tests should be ordered every 3 to 6 months:

• Serum PTH and 25-hydroxy Vitamin D levels
• Serum calcium and phosphorus levels More frequent measurement may be required during dose titration stages of certain medications or based on clinical judgment 4.