Does Parathyroid Hormone (PTH) cutoff change?

From the Guidelines

The PTH cutoff values can change based on several factors, including the specific laboratory performing the test, the assay method used, and clinical context, and typically range from approximately 10-65 pg/mL, but these reference ranges may vary between different healthcare facilities. The interpretation of PTH levels should take into account the clinical context, including the patient's calcium and vitamin D status, as well as the stage of kidney disease if applicable 1. For example, high calcium with high PTH suggests primary hyperparathyroidism, while high PTH with low calcium may indicate secondary hyperparathyroidism.

Some key points to consider when interpreting PTH levels include:

• The relationship between PTH and calcium levels is physiologically important, and PTH levels should be interpreted in conjunction with calcium levels 1
• Vitamin D status affects PTH interpretation, as vitamin D deficiency can lead to elevated PTH levels 1
• Different target ranges for PTH may be used depending on the stage of kidney disease, and the specific reference range provided by the laboratory should be checked when interpreting PTH results 1
• The use of absolute cutoff values in guidelines should be avoided due to the challenges in PTH measurement, and instead, trends in PTH levels should be monitored 1

In terms of specific cutoff values, the National Institute for Health and Care Excellence guideline recommends starting cinacalcet treatment when PTH reaches 85 pmol/L (corresponding to 802 pg/mL, ~10 times the upper reference limit) and when SHPT is refractory to other treatments and surgery is contraindicated 1. However, it is essential to consider the clinical context and the specific laboratory reference range when interpreting PTH levels. Therefore, it is crucial to interpret PTH levels in the context of the individual patient's clinical situation, rather than relying solely on absolute cutoff values.

From the FDA Drug Label

Cinacalcet (or placebo) was initiated at a dose of 30 mg once daily and titrated every 3 or 4 weeks to a maximum dose of 180 mg once daily to achieve an iPTH of ≤ 250 pg/mL The Parathyroid Hormone (PTH) cutoff is ≤ 250 pg/mL.

• This cutoff is used as a target for treatment with cinacalcet in patients with secondary hyperparathyroidism on dialysis.
• The dose of cinacalcet is titrated to achieve this target iPTH level, with a maximum dose of 180 mg once daily 2.

From the Research

Parathyroid Hormone (PTH) Cutoff Change

• The determination of parathyroid hormone (PTH) is essential for exploring phosphocalcic disorders, especially in patients with renal failure 3.
• Different generations of PTH assays can produce varying results, with the second generation potentially overestimating PTH levels beyond 200 pg/mL 3.
• The introduction of a new PTH assay generation in clinical practice should be carried out with caution, as it may lead to discrepancies in diagnosis and treatment of CKD-mineral and bone disorder (CKD-MBD) 3.
• Blood handling and specimen type can also significantly influence PTH concentrations, with citrate plasma producing lower results than serum or EDTA plasma 4.
• The variability in PTH measurements can be large enough to potentially influence clinical decision making, highlighting the need for standardized collection methods 4.

Clinical Implications

• The classification of patients according to Kidney Disease Outcomes Quality Initiative cutoff values can be affected by the choice of assay and blood specimen type 4.
• Up to 11 of 34 patients may be classified in different categories with some assays, and up to 7 of 34 with different blood specimen types 4.
• The use of serum PTH is recommended over EDTA or citrate plasma in routine practice 4.
• The lack of standardization in PTH assays can complicate the interpretation of results, emphasizing the need for caution when introducing new assay generations 3.