Impact of underfilling heparinized collection tubes on ionized calcium measurements.
Author(s): Tung JK, Bowen RAR
Publication: Clin Chim Acta, 2019, Vol. , Page
PubMed ID: 31782994 PubMed Review Paper? No
Purpose of Paper
This paper investigated the effect of underfilling lithium heparin and sodium heparin blood collection tubes on the measurement of ionized calcium in blood. Ionized calcium levels in blood were compared to those in serum from properly filled specimens collected in serum separator tubes (SSTs).
Conclusion of Paper
Mean ionized calcium concentrations were significantly lower in lithium heparin (Li-Hep) tubes compared to sodium heparin (Na-Hep) tubes containing the same volume of blood. Although mean ionized calcium concentrations were lower for all blood volumes in Na-Hep and Li-Hep tubes compared to SST specimens, the differences were only clinically significant in the the Na-Hep tubes that were 87.5% and 75% underfilled and only the Li-Hep tubes that were 75% and 50% underfilled. Significant differences in pH were observed for blood collected in Na-Hep and Li-Hep tubes compared to serum from SST specimens, but the differences were only clinically significant in Na-Hep and Li-Hep tubes filled with 0.5 mL of blood.
Studies
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Study Purpose
This study investigated the effect of underfilling lithium heparin and sodium heparin blood collection tubes on the measurement of ionized calcium in blood. Ionized calcium levels in blood were compared to those in serum from properly filled specimens collected in serum separator tubes (SSTs). Whole blood was collected from 20 healthy volunteers using a 21-gauge butterfly needle into blood collection tubes at different volumes. First, a “full-draw” of blood was collected in a 5 mL serum separator tube (SST) as a control and then 4.0, 2.0, 1.0, and 0.5 mL was collected into separate 4 mL Vacutainer sodium heparin (Na-Hep) blood tubes and 2.0, 1.0, and 0.5 of blood was collected in separate 2 mL Vacutainer lithium heparin (Li-Hep) tubes. All tubes were thoroughly mixed to distribute the heparin and minimize the formation of microclots. The serum was allowed to clot in the SST tubes for 60 min before centrifugation at 4000 rpm for 5 min. Ionized calcium concentrations and pH were measured using a blood gas analyzer within 15 min of collection for the Na-Hep and Li-Hep tubes and 70 min for the SST tubes.
Summary of Findings:
Mean ionized calcium concentrations were significantly lower for all blood volumes collected in Na-Hep and Li-Hep tubes (P<0.0001, all) compared to SST specimens, but only the Na-Hep tubes that were 87.5% (0.5 mL) and 75% (1 mL) underfilled and only the Li-Hep tubes that were 75% (0.5 mL) and 50% (1 mL) underfilled showed a clinically significant difference (≥0.1 mmol/L) compared to SST specimens. Importantly, the mean differences in ionized calcium concentration in Li-Hep tubes were significantly lower than Na-Hep tubes containing the same volume of blood (P<0.001). While the Na-Hep and Li-Hep tubes collected with 2.0 mL did not have a statistically significant difference in mean pH compared to SST specimens, significant differences were observed for the Na-Hep tubes containing 0.5 mL, 1.0 mL, and 4.0 mL of blood and Li-Hep tubes with 0.5 and 1 mL of blood (P<0.0001, all), but only the differences in Na-Hep and Li-Hep tubes filled with 0.5 mL of blood were clinically significant (≥0.1 pH unit from SSTs).
Biospecimens
Preservative Types
- None (Fresh)
Diagnoses:
- Normal
Platform:
Analyte Technology Platform Small molecule Clinical chemistry/auto analyzer Pre-analytical Factors:
Classification Pre-analytical Factor Value(s) Biospecimen Acquisition Type of collection container/solution 5 mL serum separator tube (SST)
4 mL Vacutainer sodium heparin blood tube
2 mL Vacutainer lithium heparin tube
Biospecimen Aliquots and Components Aliquot size/volume 0.5 mL
1 mL
2 mL
4 mL
5 mL
Biospecimen Acquisition Anticoagulant Lithium heparin
Sodium heparin
Biospecimen Aliquots and Components Blood and blood products Whole blood
Serum