Journal of Clinical Laboratory Analysis 0: 1–4 (2014)
Assessment of Becton Dickinson Plain and Serum Separator
Tubes in Measurement of 25-Hydroxyvitamin D3 (25OHD3) by
HPLC and Immunoassay Methods
Anwar Borai,1 Suhad Bahijri,2 Callum Livingstone,3 ∗ Mustafa Nawajha,1 Ali Bawazeer,1
Ziad Baarmah,1 Ahmed Shanaa,4 Ibrahim Kadam,1 and Mohamed Abdelaal1
1
King Abdullah International Medical Research Center, King Saud bin Abdulaziz University for Health
Sciences, Pathology King Abdulaziz Medical City, Jeddah, Saudi Arabia
2
Department of Clinical Biochemistry, Faculty of Medicine and Nutrition and Food Research Unit, King
Fahd Medical Research Center, Jeddah, Saudi Arabia
3
Department of Clinical Biochemistry, Royal Surrey County Hospital NHS Trust, Guildford, UK
4
King Faisal Specialist Hospital and Research Center, Jeddah, Saudi Arabia
Background: The accuracy of 25hydroxyvitamin D3 (25OHD3) measurement on specimens collected into serum
separator tubes (SSTs) has been questioned because of possible interference
by the gel. Possible interference was investigated in SSTs from Becton Dickinson
(BD). Design and methods: Blood specimens were collected simultaneously from
50 normal subjects into plain tubes and
SSTs. 25OHD3 was assayed on serum
using high performance liquid chromatography (Chromsystems), and Architect (Abbott) and Liaison (Diasorin) immunoassays.
Results: There were no significant differences between 25OHD3 results (means
± SE, nmol/l) obtained from specimens
collected into plain tubes and SSTs assayed by HPLC (39.0 ± 2.7 vs. 39.3
± 2.7), Liaison (32.9 ± 2.2 vs. 32.8 ± 2.3),
or Architect (43.1 ± 2.8 vs. 43.2 ± 2.8).
In specimens collected into plain tubes
and SSTs, 25OHD3 measurements by
HPLC correlated significantly (P < 0.0001)
with those from the Architect (r = 0.895,
r = 0.908) and Liaison (r = 0.907, r =
0.913), respectively. Conclusions: The gel
in SSTs (BD) does not interfere with the
measurement of 25OHD3 by HPLC or common immunoassays. This important finding
may enable clinical laboratories to make
cost savings by using SSTs without concerns about inaccuracy. J. Clin. Lab. Anal.
C 2014 Wiley Periodicals, Inc.
0:1–4, 2014.
Key words: 25OHD3; Becton Dickinson; plain tubes, SSTs; vitamin D
Vitamin D has a physiological role in calcium
homeostasis and bone turnover (1). Its insufficiency
is implicated in numerous clinical disorders (2).
The main vitamin D metabolites are cholecalciferol
(25-hydroxyvitamin D3 (25OHD3)) and ergocalciferol
(25-hydroxyvitamin D2 (25OHD2)). 25OHD3 is produced from 7-dehydrocholesterol in the skin (3) whereas
25OHD2 is derived from plants. Both 25OHD3 and
25OHD2 are used as supplements but 25OHD3 is
considered the more potent (4). HPLC and liquid chromatography-tandem mass spectrometry (LCMS/MS) are still considered the reference methods for vitamin D measurement. Commercial immunoassays were
later developed to satisfy increased demand for 25OHD
measurement.
C 2014 Wiley Periodicals, Inc.
It has recently become common practice to collect blood
into serum separator tubes (SSTs) containing a barrier gel
that separates the blood clot from serum following centrifugation. Although this method is convenient, there
have been concerns about possible analytical interference from the gel. Manufacturers of SSTs do not always
provide information on the effect of the gel on 25OHD3
Grant sponsor: King Abdullah International Medical Research Center.
∗ Correspondence to: Callum Livingstone, Department of Clinical Biochemistry, Royal Surrey County Hospital NHS Trust, Guildford, GU2
7XX, UK. E-mail: callum.livingstone@nhs.net
Received 22 April 2014; Accepted 11 August 2014
DOI 10.1002/jcla.21805
Published online in Wiley Online Library (wileyonlinelibrary.com).
2
Borai et al.
measurement by HPLC (5, 6). However, there have been
reports of gel interference with measurement of 25OHD
by both HPLC (7) and LC-MS (8). No study has carried
out a comprehensive investigation of the effect of SSTs
on the estimation of 25OHD3 by HPLC or immunoassay
methods. The purpose of the present study was therefore to determine whether SSTs influenced the 25OHD3
concentration. A secondary aim of the study was to
evaluate bias of the immunoassay techniques compared to
HPLC.
Blood specimens were collected from 50 healthy volunteers (22 males, 28 females, aged 42.6 ± 11.2 and
BMI 27.4 ± 5.2 kg/m2 ), ten of whom were taking
25OHD3 supplements. All subjects gave signed informed
consent for participation and the study was approved
by the Research Ethics Committee at King Abdullah
International Medical Research Center, Jeddah, Saudi
Arabia. Blood specimens were simultaneously collected
into plain vacutainer tubes and SST II advance vacutainer tubes using a standard venesection procedure. Vacutainers were from Becton Dickinson (BD). Specimens
were centrifuged within 1 h of blood collection and the
serum transferred into secondary tubes. Serum was stored
at −80°C until analysis 6 months later. Previous studies have observed that vitamin D is stable under these
conditions (9, 10).
The HPLC instrument was from Waters Corporation,
Milford, MA (Alliance) using a Chromsystems reagent kit
(Chromsystems Instruments and Chemical GmbH, Munich, Germany), which enables simultaneous chromatographic determination of 25OHD2 and 25OHD3 using
UV detection. Calibrators, controls, precipitation solution, wash buffers, elution buffer, mobile phase, and internal standard (IS) were also from Chromsystems. Solidphase extraction was used to remove interferents and
concentrate the analytes. Retention times of 25OHD2,
25OHD3, and IS were approximately 4.2, 4.6, and 7.1 min,
respectively. Chromatographic separation required about
12 min. The manufacturer’s intra-assay coefficient of variation (CV) was 0.9–3.0% and interassay CV was 2.3–3.3%.
The Liaison (Diasorin Inc., Stillwater, Italy) measures
25OHD by chemiluminescent immunoassay (CLIA). It is
a direct competitive assay that measures active vitamin D
forms (25OHD2 and 25OHD3) equally (intra-assay CV =
2.9–5.5% and interassay CV = 6.3–12.9%). The Architect
25OHD method uses a chemiluminescent microparticle
immunoassay (CMIA; Abbott Laboratories, Wiesbaden,
Germany) for the quantitative determination of total vitamin D metabolites in human serum (intra-assay CV =
1.4–3.7% and interassay CV = 2.7–4.6%).
SPSS version 20 was used for statistical analysis. Data
were transformed using natural logarithm (Ln) to approximate a normal distribution. Associations between variables were examined using Pearson’s correlation coeffiJ. Clin. Lab. Anal.
cients. Comparisons between means were performed by
paired Student’s t-tests at 95% confidence interval. Slope,
intercept, and correlation coefficients were calculated using the same program. Method comparisons were based
on the Bland and Altman (11) and analyzed using MedCalc statistical software version 12.7.5.
There were no significant differences between 25OHD3
results (means ± SE, nmol/l) obtained from specimens
collected into plain tubes and SSTs assayed by HPLC
(39.0 ± 2.7 vs. 39.3 ± 2.7), Liaison (32.9 ± 2.2 vs.
32.8 ± 2.3), or Architect (43.1 ± 2.8 vs. 43.2 ± 2.8).
On examining results obtained from specimens collected
into plain tubes, there was a significant correlation
(P < 0.0001) between those from HPLC and from
the Architect analyzer (r = 0.895; intercept = 1.733;
slope = 0.864) and between HPLC and the Liaison analyzer (r = 0.907; intercept = 3.378; slope = 1.083).
Similarly, when SSTs were used, there was a significant
correlation (P < 0.0001) between HPLC and the Architect
analyzer (r = 0.908; intercept = 1.099; slope = 0.883) and
between HPLC and the Liaison analyzer (r = 0.913; intercept = 5.154; slope = 1.042). When compared to HPLC,
results from the Liaison analyzer correlated more strongly
than did those form the Architect, irrespective of whether
plain tubes or SSTs were used. In specimens collected into
plain tubes (Fig. 1A), there was good agreement between
the Liaison assay and HPLC with little variation at high
concentrations. The Architect assay showed a clear positive bias at high 25OHD3 concentrations. Similar results
were obtained for SSTs (Fig. 1B).
The use of SSTs is logistically advantageous because use
of the primary tube for testing reduces consumable costs
and processing time. However, it is important to exclude
the possibility of gel interference with measurement. The
data showed clearly that SSTs had no effect on serum
25OHD3 concentrations as measured by HPLC or either
of the two immunoassays (Liaison and Architect). We
conclude therefore that it is appropriate to collect blood
into a single SST for both routine biochemical analyses
and measurement of 25OHD3. This is an important finding because of the cost savings that can be made by using
a single tube for multiple tests, particularly in view of the
increase in 25OHD3 requests in recent years (12, 13).
The correlation between 25OHD concentrations estimated by LC-MS or HPLC, and various immunoassay
platforms have been investigated previously (14–17). The
results of our correlation analyses agreed well with those
reported by Ferrell et al. (18), and with evaluation reports on the Liaison (19) and Architect analyzers (20). Although there were small differences in the strength of correlation of results from HPLC and immunoassay instruments, it appears that sample collection into either tube
type is acceptable, irrespective of the analytical method
used. Bland–Altman plot analysis showed that the
25OHD3 and Serum Separator Tubes
3
Fig. 1. Bland–Altman plot for 25OHD3 results obtained from 50 subjects using the Liaison (Diasorin) and Architect (Abbott) immunoassays
compared to HPLC (Chromsystems). (A) Plain tubes: HPLC versus Liaison and Architect. (B) SSTs: HPLC versus Liaison and Architect.
Liaison analyzer agreed better with HPLC with very little variation at high levels. The Architect analyzer agreed
well with HPLC at low 25OHD3 but with more variation
at high concentrations. The observed differences between
these methods emphasize the importance of interpreting
results using method-specific reference ranges.
Future studies are warranted to investigate the effect
of SSTs on 25OHD2 measurement so that guidance can
J. Clin. Lab. Anal.
4
Borai et al.
be provided to clinical laboratories in countries where
this form of the vitamin is taken supplementally. Another
factor reported to influence 25OHD3 measurement is vitamin D binding protein (DBP) (17). This also demands
further study. A limitation of the present study was that
LC-MS measurement of 25OHD3 was not included in
the comparison. Its principle of measurement is different
from those of the methods used in this study. In order to
ensure wide applicability of the findings, the study was
performed on the commonly used BD tubes. However, it
should be emphasized that the results are not necessarily
applicable to gel tubes produced by other manufacturers.
BD gel separators do not interfere with the measurement of 25OHD3 when the analysis is carried out by
HPLC or common immunoassay methods. This important finding may enable clinical laboratories to make cost
savings without concerns about inaccuracy of measurements.
ACKNOWLEDGMENTS
The authors acknowledge the unlimited support received from King Abdullah International Medical Research Center (KAIMRC), Jeddah, Saudi Arabia. The
authors are also grateful to Abbott and Diasorin whose
representatives in Saudi Arabia kindly provided vitamin
D assay materials used in the study (Medi-Serve and Abdullah Fouad Co.).
Ethical approval: The study was approved by the Research Ethics Committee at King Abdullah International
Medical Research Center, Jeddah, Saudi Arabia.
CONFLICT OF INTEREST
The authors declare no conflict of interest.
REFERENCES
1. Holick MF. Vitamin D deficiency. N Engl J Med 2007;357:
266–281.
2. Zhang R, Naughton DP. Vitamin D in health and disease: Current
perspectives. Nutr J 2010;9:1475–2891.
3. Holick MF. Environmental factors that influence the cutaneous
production of vitamin D. Am J Clin Nutr 1995;61:638S–645S.
J. Clin. Lab. Anal.
4. Armas LA, Hollis BW, Heaney RP. Vitamin D2 is much less
effective than vitamin D3 in humans. J Clin Endocrinol Metab
2004;89:5387–5391.
5. 25-OH Vitamin D3 HPLC Assay KEB, Inc. Available from: http://
stores.eaglebio.com/images/VD331-H100.pdf.
Accessed
on
October 2013.
6. Evacuated Blood Collection System For In Vitro Diagnostic Use Gb-o. Available from: http://www.gbo.com/documents/
980200_IFU_VenousBloodCollection_rev11_GB.pdf. Accessed on
October 2013.
7. Lensmeyer GL, Wiebe DA, Binkley N, et al. HPLC method for 25hydroxyvitamin D measurement: Comparison with contemporary
assays. Clin Chem 2006;52:1120–1126.
8. Elder PA, Lewis JG, King RI, Florkowski CM. An anomalous
result from gel tubes for vitamin D. Clin Chim Acta 2009;410:95.
9. Colak A, Toprak B, Dogan N, Ustuner F. Effect of sample type,
centrifugation and storage conditions on vitamin D concentration.
Biochem Med (Zagreb) 2013;23:321–325.
10. Wielders JP, Wijnberg FA. Preanalytical stability of 25(OH)vitamin D3 in human blood or serum at room temperature: Solid
as a rock. Clin Chem 2009;55:1584–1585.
11. Bland JM, Altman DG. Statistical methods for assessing agreement
between two methods of clinical measurement. Lancet 1986;1:307–
310.
12. Mula-Abed WA. 25- hydroxyvitamin d: Explosion in clinical interest and laboratory requests. Oman Med J 2009;24:239–241.
13. Krasowski MD. Pathology consultation on vitamin D testing. Am
J Clin Pathol 2011;136:507–514.
14. Hermida FJ, Fernandez M, Laborda B, et al. Assessment of ADVIA
Centaur analyzer for the measurement of 25-OH vitamin D. Clin
Lab 2012;58:987–995.
15. Mochizuki A, Kodera Y, Saito T, et al. Preanalytical evaluation of
serum 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 measurements using LC-MS/MS. Clin Chim Acta 2013;420:114–120.
16. Koivula MK, Matinlassi N, Laitinen P, Risteli J. Four automated
25-OH total vitamin D immunoassays and commercial liquid chromatography tandem-mass spectrometry in Finnish population. Clin
Lab 2013;59:397–405.
17. Heijboer AC, Blankenstein MA, Kema IP, Buijs MM. Accuracy
of 6 routine 25-hydroxyvitamin D assays: Influence of vitamin D
binding protein concentration. Clin Chem 2012;58:543–548.
18. Farrell CJ, Martin S, McWhinney B, Straub I, Williams P, Herrmann M. State-of-the-art vitamin D assays: A comparison of automated immunoassays with liquid chromatography-tandem mass
spectrometry methods. Clin Chem 2012;58:531–542.
19. D-Facts Vitamin D Competitive Evaluation. Available at:
http://wwwilmarorgil/diasorin/D-fact_Competitive_Eval0112
pdf. Accessed on October 2013.
20. Wallace AM, Gibson S, de la Hunty A, Lamberg-Allardt C, Ashwell
M. Measurement of 25-hydroxyvitamin D in the clinical laboratory:
Current procedures, performance characteristics and limitations.
Steroids 2010;75:477–488.