Differences between serum and plasma for intact parathyroid hormone measurement in patients with chronic renal failure in routine clinical practice

Abstract

Background: Parathyroid hormone (PTH) is important in the evaluation of patients with calcium metabolism disorders and/or chronic renal disease. Aims: To assess the differences between serum and plasma PTH measurements using the Advia Centaur. Methods: Twenty six paired serum and edetate samples from patients with chronic renal failure were analysed using the Advia Centaur. Results: The EDTA results ranged from 2.3 to 76.1 pmol/litre and the Deming regression equation was: serum = 0.8927 EDTA 2 0.447. The percentage difference plot had a mean difference of 13.8% (95% confidence interval, 2.2% to 25.4%; significant). The available time to separation and freezing ranged from 10 to 231 (median, 85) minutes. The correlation coefficient for the percentage difference against the time to separation and the percentage difference against the mean PTH concentration were 20.13 and 20.07, respectively. Conclusions: These results go beyond the previous controlled research conditions by showing that such differences between serum and edentate plasma exist in routine clinical practice. They also show that intra-individual PTH differences as large as 25.0% can exist on the same day between serum and edetate plasma. This may partly explain some of the variability of PTH concentrations found in some patients with chronic renal failure.

Performance Characteristics of Six Intact Parathyroid Hormone Assays

“…5,[8][9][10][11][16][17][18][19] The majority of previous studies performed the comparison on patients undergoing hemodialysis or with other disease, whereas our study used remains controversial on the threshold used to define vitamin D insufficiency, some have suggested using a 25OHD cutoff of 20 ng/mL (50 nmol/L). 21 At this cutoff, most methods had a PTH upper reference limit that overlapped with the 90% confidence interval for the other 25OHD cutoffs.…”

Interpretation of serum parathyroid hormone concentrations in dialysis patients: what do the KDIGO guidelines change for the clinical laboratory?

“…Finally, preanalytical considerations must be taken into account, specially the nature of the blood sample. Significant differences in PTH concentrations measured in serum and EDTA plasma have been reported with some assays, such as the Immulite PTH assay (25)(26)(27). To account for these differences, the manufacturer proposes normal values that are different for serum and EDTA plasma, with the consequent differences for the KDIGO target range for dialysis patients.…”

Mysterious PTH values after parathyroidectomy in a patient on maintenance dialysis

“…As it is essential to accurately measure the concentration of PTH to monitor progression of disease, guide treatment, and evaluate response to therapy in patients with CKD, it is important to understand how the result can be falsely affected at different levels. Table 1 summarizes the most common reasons contributing to fluctuating PTH results and potential misinterpretation: the correct technique of specimen drawing or handling, the difference in serum versus plasma samples, 15 laboratory errors, multiple marketed iPTH assays, which are not comparable, volatility of the PTH results due to physiological factors such as fluctuating Ca and P levels, vitamin D and/or calcimimetic therapy, the short half‐life, and accumulation of fragments in CKD, which are measured to various degrees dependent on the assay used (Table 1). Values obtained with different assay methods cannot be used interchangeably until a standardized test is available 16,17 …”