Serum GFAP - reference interval and preanalytical properties in Danish adults.
Author(s): Tybirk L, Hviid CVB, Knudsen CS, Parkner T
Publication: Clin Chem Lab Med, 2022, Vol. , Page
PubMed ID: 36067832 PubMed Review Paper? No
Purpose of Paper
The purpose of this paper was to compare glial fibrillary acidic protein (GFAP) levels in serum obtained after a room temperature pre-centrifugation delay of up to 9 h, in serum stored at room temperature for up to 7 days, at-20°C for up to 133 days, or after up to 3 freeze-thaw cycles. Age-specific reference intervals for GFAP were also calculated.
Conclusion of Paper
The authors calculated the following age-specific reference intervals for GFAP levels in serum: 25–136 ng/L (20-39 years of age), 34–242 ng/L (40-64 ears of age), and 5–438 ng/L (65–90 years of age); the authors state there were no gender-based differences in GFAP reference levels. The variability of GFAP reference intervals for serum increased with patient age. Changes in GFAP levels remained within the maximum allowable bias (10.2%) when blood was stored for ≤9 h at room temperature before centrifugation, when serum was stored at room temperature for ≤7 days, when serum was stored at -20°C for ≤133 days, when serum was subjected to ≤2 freeze-thaw cycles, and after addition of hemolysate. However, the increase in GFAP levels observed when serum was stored at -20°C for 133 days or subjected to 3 freeze-thaw cycles exceeded the maximum allowable bias.
Studies
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Study Purpose
The purpose of this study was to compare GFAP levels in serum obtained after a room temperature pre-centrifugation delay of up to 9 h, in serum stored at room temperature for up to 7 days, at-20°C for up to 133 days, or after up to 3 freeze-thaw cycles. Age-specific reference intervals for GFAP were also calculated. Blood was collected into BD Vacutainer serum clot activator tubes from the antecubital vein of 254 blood donors (20-65 years) and 117 outpatients older than 65 years of age without evidence of diabetes or neurological conditions. Serum was separated by centrifugation at 3000 g for 5 min and frozen at -20°C for <2 months within 7 h of blood collection unless otherwise specified. The effects of pre-centrifugation storage and serum storage at room temperature were investigated by storing blood from inpatients (diagnosis not specified) that were 30 (3 patients), 50-60 (3 patients), or >80 years old (4 patients) at room temperature for 1, 2, 5, 7 and 9 h before serum isolation; and storing serum (separated from blood within 1 h of collection) at room temperature for 0, 1, 2, 3, 5 and 7 days before freezing at -20°C. The effects of storing serum at -20°C was investigated by storing pooled serum with different GFAP levels (no other details provided) at -20°C for 0 (fresh), 1, 2 and 4.5 months. The effect of freeze thaw cycling was investigated by freeze-thaw cycling pools of serum between room temperature and -20°C once, twice, and three times. To investigate effects of hemolysis, 800 mg/dL hemolysate was added to pools of serum with low, medium or high GFAP levels (no other details of pools provided) and subsequent serial dilution of the serum pools to obtain hemoglobin levels of 11.6, 28.6, 53.2, 101.5, 20.0 and 386.9 mg/dL. GFAP levels were quantified using the Simoa GFAP Discovery Kit on an HD-1 autoanalyzer.
Summary of Findings:
The authors calculated the following age-specific reference intervals for GFAP levels in serum: 25–136 ng/L (20-39 years of age), 34–242 ng/L (40-64 years of age), and 5–438 ng/L (65–90 years of age); the authors stated there were no gender-based differences in GFAP reference levels. Variability in GFAP reference intervals increased with patient age. Storage of blood for 2, 5, 7 and 9 h at room temperature before centrifugation led to average increases of 2.5%, -0.1%, 2.9% and 2.3%, respectively in serum GFAP levels. Similarly, GFAP levels in serum stored at room temperature for 1, 2, 3, 7 days had average changes of -4.3%, -0.6%, -1.4%, 1.4% and 3.1%, respectively. Storage of serum at -20°C for 42, 57 and 133 days resulted in average changes in GFAP levels of -7.7%, -7.8% and 10.4%, respectively; and 1, 2 and 3 freeze-thaw cycles resulted in average changes of 5.5%, 8.6% and 1.4%, respectively. Importantly, notable changes (that exceeded the maximum allowable bias of 10.2%) were limited to those observed after serum was stored at -20°C for 133 days or after serum underwent three freeze-thaw cycles. A slight increase in GFAP levels was observed in most serum specimens after addition of hemolysate, but the effect did not increase with increasing hemoglobin level and remained within the maximum allowable bias.
Biospecimens
Preservative Types
- None (Fresh)
- Frozen
Diagnoses:
- Not specified
- Normal
Platform:
Analyte Technology Platform Protein Clinical chemistry/auto analyzer Pre-analytical Factors:
Classification Pre-analytical Factor Value(s) Preaquisition Patient age 20-39 years
40-64 years
>65 years
Preaquisition Patient gender Female
Male
Storage Storage temperature Room temperature
-20°C
Biospecimen Aliquots and Components Hemolysis No hemolysate added
Hemolysate added
Storage Storage duration 0 days
42 days
57 days
133 days
Storage Time at room temperature 1 h
2 h
5 h
7 h
9 h
0 days
1 days
2 days
3 days
7 days
Storage Freeze/thaw cycling 0 cycles
1 cycle
2 cycles
3 cycles