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Abstract

Introduction

The pneumatic tube system (PTS) is an automated and fast modality of transportation of biological samples, but it has been reported to induce preanalytical errors.

Aim

To study the influence of transportation by PTS on biochemistry tests which are particularly sensitive to haemolysis and atmospheric pressure variation.

Materials and methods

We compared laboratory results of arterial blood gas, sodium, potassium, chloride, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, glucose and haemolysis index of samples conveyed simultaneously by PTS and by courier.

Results

We recruited 30 patients from the sampling room and 40 patients from the intensive care unit. Transport through PTS resulted in a significant increase in aspartate aminotransferase and potassium without exceeding the limits of acceptability. Potassium was significantly more increased for samples transported in a higher speed line (p = .048) but without exceeding the limits of acceptability. No significant impact was noted on haemolysis indices. The pO₂ variations due to PTS transportation exceeded the limit of acceptability with significant intra-individual variations.

Conclusion

Our PTS is validated for biochemistry tests results. It reduces turnaround times without affecting sample quality. However, the interpretation of arterial blood gas results should be careful for samples transported by PTS.

Keywords

Pneumatic tube system preanalytical phase haemolysis biochemistry tests arterial blood gas

Introduction

Improving turnaround time is essential for laboratory quality management.¹ Thus, pneumatic tube systems (PTS) are frequently used to control the time of biological samples transportation in hospitals. PTS is an automated and fast delivery system from phlebotomy site or clinical departments to laboratories.² It significantly saves time to report results and ensures better organization in hospital structures.³

However, this mode of transport can lead to errors in the preanalytical phase.^2,4 Depending on the system configuration, the transported samples can be subject to physical forces such as sudden acceleration/deceleration waves, changes in direction, long distances, high speeds, temperature changes, atmospheric pressure changes generated by the vacuum system and blood movement in tubes and vibrations.⁵ These forces can potentially affect the quality and integrity of the samples essentially by causing haemolysis^2,4 and changes in blood gas parameters.⁶

The characteristics of the PTS vary from one system to another. Verification should be performed on each PTS and during eventual modification of system parameters.⁷ The requirements of ISO 15189 standard imply managing effectively this preanalytical device.

The aim of this study was to investigate the influence of PTS transport on biochemical tests, particularly those sensitive to haemolysis and atmospheric pressure variation.

Materials and methods

This is a cross-sectional study carried out in the Clinical Chemistry Laboratory. We recruited unselected adult volunteers from the sampling room and patients from the medical intensive care unit. Demographic and clinical data was not collected.

Materials

In the sampling room, three tubes were collected for each subject. All samples were taken by the same experienced phlebotomist by a single puncture at the elbow fold with needle collection device and collected on lithium heparinate tubes. In order to minimize as much as possible any other known factors of haemolysis, the tourniquets were loosened from the beginning of filling and the tubes were stirred by slow flips. All subjects were informed about the purpose of the study and had given oral consent. For each of the patients hospitalized in the intensive care unit, two duplicate arterial samples were taken by the nurses of the department at the femoral artery, in syringes containing heparin (heparin sodium 5000UI). Strict anaerobic conditions were respected.

The samples were immediately transported in two paths, through the PTS and on foot at room temperature, to the laboratory from the same pneumatic line.

The PTS studied (Aerocom ®) is a bidirectional network of tubes in which sample transport vectors (cartridges or capsules) are transported between transmitting and receiving stations located, respectively, in clinical departments and laboratories. The PTS is composed of a main station ‘the turbine’ (which generates a flow of compressed air to ensure the movement of cartridges), 23 peripheral stations, six exchangers and sensors. A computer system manages the PTS and ensures the traceability of all shipments. Due to the RFID (Radio Frequency Identification) electromagnetic chips on the cartridges, their movements are detected by sensors installed at each station. We conducted our study on three lines of the PTS whose characteristics are summarized in Table 1.

• Line 1: (from the sampling room to our laboratory) was chosen for the largest number of samples received on this line.

• Line 2: (from the cardiovascular surgery department to our laboratory) was analysed for its longest length travelled.

• Line 3: (from the medical intensive care unit to our laboratory) for blood gas samples.

Table 1.

Characteristics of the three lines of the pneumatic system.

	Line 1	Line 2	Line 3
Distance (m)	80	385	306
Speed (m/s)	11.4	6.4	4.4
Time (s)	7	60	70
Number of exchangers	0	5	6

m: metre; m/s: metre per second; s: second.

For the three lithium heparinate tubes collected for each subject, one tube was transported by line 1, one tube by line 2 and the third by foot. Line 2 has a longer distance and transport by line 1 has a higher speed.

For syringes, one was transported by line 3 and the other by courier.

The time elapsed between taking and receiving samples at the laboratory when transported by courier was noted. The variation of the temperature of the PTS in relation to the ambient temperature was controlled using a temperature logger, introduced into the cartridge.

Methods

Samples transported by PTS stored at room temperature while awaiting the couriered samples to mimic routine conditions. The samples were analysed simultaneously under the same conditions (at the same time, and on the same centrifuges and analyzer).

The choice of parameters studied was explained by the frequency of their prescription, their sensitivity to the influence of pressure variations that may occur in the PTS or to the influence of haemolysis on their concentrations.

These parameters were:

- Arterial blood gas (blood acidity (pH), oxygen partial pressure (pO₂) and carbon dioxide partial pressure (pCO₂) on the ABL800 Flex® Radiometer analyzer.

- Sodium, potassium, chloride, lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT) and blood glucose were run on Roche Cobas C501 chemistry analyser (Roche Diagnostics GmbH, Mannheim, Germany).

- The haemolysis index (HI) is a semi-quantitative indicator that assesses the degree of potential interference due to haemolysis.² It was determined for lithium heparinate tube samples, on Roche Cobas C501 chemistry analyser (Roche Diagnostics GmbH, Mannheim, Germany). HI is approximately equivalent to haemoglobin concentration of 1000 mg/dL. Manufacturer HI cut-offs were used.

Statistical analysis

The statistical analysis was performed with the Statistical Package for Social Sciences ® (SPSS) software (version 20.0). The hypothesis of the normality of the distribution was evaluated by the Shapiro–Wilk test. Data was presented as mean ± standard deviation (SD) or as median and interquartile range (IQR) when parameters were Gaussian or non-Gaussian distributed, respectively. We used Student's T-test or Wilcoxon's non-parametric test (for normal or non-normal distribution parameters, respectively) for the comparison of the matched samples of the two transport modalities (by courier and by PTS) and the two different lines of the PTS (by line 1 and line 2) for the triplet samples to study the effect of distance travelled and speed on biochemical tests. A difference between the results was considered significant for a p-value < .05.

For each parameter, we calculated the bias (%) (the average percentage of differences) according to the formula and taking into account courier transport values considered as reference values (C) and pneumatic transport values (P): Bias (%) = [(P-C)/C] x 100

The limit of acceptability for interpreting the results was the total acceptable limit variation (TALV). We compared the biases (%) obtained compared to TALV to assess clinical impact. Thus, the variation induced by the PTS routing was considered significant if exceeding the TALV. The TALV was calculated for each parameter and was expressed as a percentage (%) (Appendix 1).

T A L V = \sqrt{(2.77 CVa) 2 + (0.5 CVb) 2}

The TALV takes into account two criteria:

- Analytical variability limit = ± 2.77 CVa (CVa = mean coefficient of variation (CV) of intermediate fidelity (%) (all levels combined)).

- The limit biological variability = ± 0.5 CVb (CVb = intra-individual CV): expressed according to the tables of Ricos et al. (2014 version)⁸

For pO₂, we compared the mean variation between the 2 transport routes with the acceptability standard proposed by the French Society Of Clinical Biology (SFBC) (CVb not determined).⁸

Results

In total, we recruited 30 patients from the sample room and 40 patients from the medical intensive care unit.

The temperature variation during the transfer from the clinical unit to the laboratory did not exceed 0.5°C (27.18 ± 0.19 °C to 27.3 ± 0.18 °C; p = .78). The transport time via PTS was significantly shorter than the courier's transport time (54 s ± 18 s vs 8 min 28 s ± 4 min 15 s; p < .001).

The results of biochemical tests of samples that were pneumatically transported by line 1 and by foot showed a statistically significant increase for AST (p = .037) and potassium (p = .029). A statistically significant increase for AST (p = .046) was found when samples were transported pneumatically via line 2. Comparing the two lines 1 and 2 of the PTS (Table 2), only potassium was significantly more increased for samples transported by line 1 compared to line 2 (p = .048). Mean bias was less than TALV for all parameters (Table 3). For each biochemical test, biases for all patients were represented in relation to the corresponding TALV (Figure 1).

Table 2.

Comparison of biochemical parameters transported by courier and by two pneumatic system lines of different characteristics.

Parameter	Courier (n = 30)	PTS line 1 (n = 30)	PTS line 2 (n = 30)	p-value
Parameter	Courier (n = 30)	PTS line 1 (n = 30)	PTS line 2 (n = 30)	Line 1 Vs Courier	Line 2 Vs Courier	Line 2 Vs line 1
Glucose (mmol/L)	6.6 (2.15) [4.9 – 23.1]^a	6.7 (1.85) [4.6 – 23.2]^a	6.65 (1.97) [4.7 – 23.4]^a	0.821	0.336	0.214
AST (UI/L)	17.5 (5) [10.1–42.1]^a	17.45 (4.075) [10.3– 42.3]^a	17.55 (4.47) [10.1 – 42.4]^a	0.037	0.046	0.446
ALT (UI/L)	14.3 (9,475) [8,5 – 32.8]^a	14.25 (10.27) [7.6 – 32.3]^a	14.4 (8.97) [8.7 – 32.6]^a	0.888	0.321	0.341
LDH (UI/L)	197.5 (53.25) [133 – 381]^a	198.5 (70.5) [140 – 412]^a	206 (69.5) [155 – 394]	0.113	0.217	0.509
Sodium (mmol/L)	139 (3) [133 – 144]^a	138.5 (3) [133 – 145]^a	139 (2.25) [133 – 144]^a	0.420	0.765	0.822
Potassium (mmol/L)	4.2 ± 0.27 [3.8 – 4.9]^b	4.3 ± 0.31 [3.8 – 5]^b	4.2 ± 0.28 [3.8 – 4.9]^b	0.029	0.851	0.048
Chlorine (mmol/L)	102.5 (2) [96 – 108]^a	103 (3) [95 – 108]^a	103 (3.5) [95 – 107]^a	0.622	0.635	0.157
HI	1.0 (2.0) [0 –27]^a	2.5 (6.0) [0 –16]^a	2 (5.0) [0 –32]^a	0.185	0.568	0.769

PTS: pneumatic tube system; AST: aspartate aminotransferase, ALT: alanine aminotransferase; HI: Haemolysis index; LDH: lactate dehydrogenase.

^aThe values were expressed in median (IQR) [min, max].

^bValues were expressed as mean ± SD [min, max]; VS.: versus.

Table 3.

Median bias relative to the calculated total acceptable limit variation (TALV).

		Glucose	AST	ALT	LDH	Na	K	Cl
Median bias [min-max] (%)	Line 1	1.91 [0-12.31]	4.47 [0-24.59]	2.56 [0-10.59]	11.30 [0-24.29]	0.49 [0-1.5]	2.01 [0-12.20]	0.45 [0-1.04]
Median bias [min-max] (%)	Line 2	1.46 [0-12.28]	4.17 [0-14.75]	3.26 [0-20]	13.55 [0-135.9]	0 [0-2.88]	1.5 [0-7.50]	1 [0-1.96]
TALV (%)		7.21	16.86	18.45	16.27	3.06	5.32	4.47

AST: aspartate aminotransferase, ALT: alanine aminotransferase; LDH: lactate dehydrogenase; Na: Sodium; K: Potassium; Cl: Chlorine; TALV: total acceptable limit variation.

Figure 1.

Representation of parameter variations according to acceptable limits. Note. The minimum and maximum acceptable limits of total acceptable limit variation (TALV) (for pO₂ according to the SFBC acceptable limits) are marked by red lines. Each dot is an individual patient bias. The dots in blue correspond to the biases in line 1. The dots in yellow correspond to the biases in line 2; AST: aspartate aminotransferase; ALT: alanine aminotransferase; LDH: lactate dehydrogenase; pH: blood acidity; pO₂: oxygen partial pressure; pCO₂: carbon dioxide partial pressure.

The median and IQR differences in HI were: 1.0 (2.0) for the walking route, 2.5 (6.0) for line 1 and 2.0 (5.0) for line 2 (Table 2). HI increased slightly by pneumatic transport (the two lines) compared to pedestrian transport but the difference was not statistically significant (Table2, Figure 2). For all samples, HI did not exceed the limits described for glucose, ALT, AST, potassium, sodium and chloride. LDH is the most sensitive parameter to haemolysis with possible interference for HI that exceeds 15 (arbitrary unit). The frequencies of the samples with an HI that exceeded the limit for the LDH were 4.93%, 3.7% and 6.66% for the pedestrian track, line 1 and line 2, respectively. For samples with HI that exceeded the limit for LDH, haemolysis was associated in only one patient with a significant change in LDH (Bias = 22%) after transport by PTS.

Figure 2.

Hemolysis index stratified by transportation modality. Note. PTS: pneumatic tube system; HI: Haemolysis index; The values were expressed in median (IQR) [min, max].

pO₂ values were significantly increased (p = .001) during transport by PTS compared to transport by courier (Table 4). No statistically significant differences were found for pH and pCO₂. The values of the pO₂ differences obtained by the two transport modalities were blotted according to the acceptable limit of the SFBC (=12.4 mmHg) (Figure 1). It was noted that 30% of pO₂ values exceeded this. Significant intra-individual variations were noted with a maximum variation of +73 mmHg (from 85.9 mmHg to 159 mmHg). The mean pH bias (=0.15%) was lower than the TALV (5.8%). The mean pCO₂ bias (=3.42%) was lower than the TALV (15.42%). All pH and pCO₂ biases were below the TALV.

Table 4.

Comparison of blood gas parameters between transport modalities (PTS Versus Courier).

Parameter	Courier (n = 40)	PTS (line 3) (n = 40)	p-value
pH	7.41 (0.06) [6.9 - 7.49]^a	7.41 (0.07) [6.9 - 7.49]^a	0.604
pO2 (mmHg)	89.43 ± 29.19^b	99.06 ± 34.33^a	0.001
pCO2 (mmHg)	37.25 (9.08) [26.8 – 57.5]^b	37.05 (10.67) [26.2 – 58.1]^a	0.069

PTS: pneumatic tube system; pH: blood acidity; pO₂: oxygen partial pressure; pCO₂: carbon dioxide partial pressure.

^aThe values were expressed in median (IQR) [min, max].

^bValues were expressed as mean ± SD.

Discussion

The installation of the PTS at our University Hospital Center managed the problems of staff shortage and organized the internal logistics of the hospital. Our study reconfirmed the effectiveness of the PTS by reporting a considerably shorter delivery time compared to the transport on foot. This has been reported in almost all publications on PTS.^3,4 To study the effect of transporting blood samples by PTS under conditions close to practice, we recruited unselected patients.

Previous studies have shown that samples transported by PTS have a significantly higher haemolysis frequency.^2,9 Several factors could induce haemolysis by pneumatic transport, such as the level of filling of the tubes and the technical characteristics of the PTS.⁴ Rapid transport of blood samples in the PTS can cause red blood cell degradation following rupture of the erythrocyte membrane associated with the release of haemoglobin and other intracellular components of erythrocytes into plasma.^2,4 In our study, HI had low values and the difference between the 2 modes of transport was not significant (Figure 2). Potassium, LDH and AST results were not influenced by changes in HI induced by PTS except the LDH result of one sample. These results are consistent with those of Fernandes' study.¹⁰ In our study, PTS transport induced minimal variations in the results of biochemical tests (Table 2) including those most likely to be affected by pneumatic transport (LDH, potassium, AST).^11,12 These variations did not exceed the TALV (Table 3).

For LDH, previous studies have shown that this is the parameter most frequently influenced by PTS.^13,14 In our study, PTS did not significantly influence LDH levels (Table 2).

It has been described that transport by PTS would have increased potassium levels.^15,16 This increase in potassium has been explained by the increase in the plasma concentrations of intra-erythrocyte compounds following cell lysis.¹⁷ In our study, the mean potassium level increased significantly when the samples were transported via line 1, but the median bias was acceptable (Table 2). This increase was not related to changes in HI. All HI determined did not exceed 32 (Manufacturer HI cut-off for potassium is 90) (Figure 2). In addition, by comparing the effect of transport by the two lines of PTS of different characteristics, the average potassium level increased significantly when the samples were transported by line 1 with a higher speed. The comparison between the two lines showed a statistically significant difference (Table 2). Indeed, the physical stress induced by PTS has been shown to be closely related to acceleration, deceleration and changes in direction. The acceleration vector (velocity) could increase haemolysis and could be considered a quality objective.⁹ Evliyaoğlu et al. found that the HI values slightly increased as the transport rate and distance of the PTS increased.¹⁸ Thus, in our study, the variation in velocity would have an effect on potassium levels but this variation would not have an impact on clinical interpretation.

Transport by PTS resulted in a statistically significant increase in AST but not exceeding the TALV (Table 3). The maximum variation of +3.5 IU/L did not impact the clinical interpretation of this test. This effect was described in several studies.^2,12 Moreover, for the studies of Poznanski et al.¹³ and Steige H and Jones JD,¹¹ the variations between courier and pneumatic transport were not significant. The variation of AST levels induced by PTS transport would be independent of the characteristics of the lines. Comparison between the two lines did not show a statistically significant difference (Table 2).

Regarding the determinations of glucose, ALT, sodium and chloride, no significant differences were found (Table 2). Our results were consistent with the results of the other studies.^2,4 These tests are not very sensitive to hemolysis.

In our study, transport by PTS had no effect on pH and pCO₂ measurements (Table 4). For pO₂, the values of the pneumatically transported samples were significantly higher than the values obtained by courier (Table 4). Variations exceeded the limit of acceptability with significant intra-individual variations (Figure 1). These results were consistent with previous studies.^19,20 The study by Peter et al.²⁰ showed that the effect of PTS on pO₂ induced significant intra-individual differences up to 40 mmHg for pO₂ measurements compared to the transport by courier. This variation could be explained by contamination by ambient air due to the effect of pressure.²⁰ Given the pO₂ of the ambient air is approximately 160 mmHg, it is likely that the rapid transit and agitation of the sample through the PTS caused the pO₂ in the syringes to be balanced with the air in the PTS cartridge. In our study, we eliminated the air bubbles and sent the syringes tightly closed. However, it is possible that “microbubbles” in the syringes combined with the effects of the pressure of the PTS caused these changes in the pO₂ values.¹⁹ In contrast, Poznanski et al.¹³ found no difference in results on pH, pCO₂ and pO₂ measurements between the two modalities of transport. The transport speed of the cartridges containing the samples was constant and low (3.6 m/s) with controlled deceleration prior to arrival at destination and wide use of padding to minimize agitation during transport.¹³ This speed was lower than the transport speed by line 3 of our study (4.4 m/s). Thus, the increase in pO₂ by PTS in our study could be caused by the relatively high transport speed.

Conclusion

The evaluation of the pneumatic transport modality showed that our PTS is validated for biochemical results. It reduces turnaround times without affecting the quality of the sample.

In addition, the interpretation of arterial blood gas results should be careful for pneumatically transported samples. This modality of transport could induce significant biases for pO₂ exceeding the limits of acceptability. This increase could be explained by the subsequent ambient air contamination to errors of the preanalytical phase. The preanalytical phase is the most vulnerable part of the entire analytical process and is considered one of the biggest challenges for the laboratory.

Footnotes

Acknowledgements

We would like to thank Mme Islem Baddel and Mme Nessrine Ben Salem for providing help in collecting samples and in laboratory assays.

Data Availability Statement

The data supporting the findings of this study are available upon reasonable request. As the data are generated and owned by the authors, there is no specific external publication or reference associated with the dataset.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethical approval

Rihab Makhlouf declares as first author.

Guarantor

RM.

Contributorship

Dr. RM was responsible for study design and conception, data analysis, interpretation, analysis and redaction of the manuscript. Dr SF and Mme ZL participated in study design and conception and redaction of the manuscript. Dr. FAM, Dr DJ, Mr LF, Dr KC and Dr. AE helped draft the manuscript. All authors read and approved the final manuscript.

Consent to participate

Participants provided oral consent.

Consent for publication

All relevant bodies and authors gave consent for publication.

ORCID iD

Rihab Makhlouf

Total acceptable limit variation (TALV)

Parameter	Mean CVa	Analytical variability limit	CV within subject⁸	TALV
Glucose	2.40	6.65	5.60	7.21
ASAT	5.67	15.70	12.30	16.86
ALAT	5.67	15.70	19.40	18.45
LDH	5.67	15.70	8.60	16.27
Sodium	1.10	3.05	0.60	3.06
Potassium	1.73	4.80	4.60	5.32
Chlorine	1.60	4.43	1.20	4.47
pH	2.00	5.54	3.50	5.81
pO₂	2.00	5.54	NA	NA
pCO₂	5.33	14.77	4.80	14.97

CVa: analytical coefficient of variation; CVb: Biological coefficient of variation; TALV: Total acceptable limit variation; NA: non-applicable.

Appendix 2

References

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Influence of pneumatic tube delivery system on laboratory results

Abstract

Introduction

Aim

Materials and methods

Results

Conclusion

Keywords

Introduction

Materials and methods

Materials

Methods

Statistical analysis

Results

Discussion

Conclusion

Footnotes

Acknowledgements

Data Availability Statement

Declaration of conflicting interests

Funding

Ethical approval

Guarantor

Contributorship

Consent to participate

Consent for publication

ORCID iD

Total acceptable limit variation (TALV)

Appendix 2

References