one study done on tube system and k

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Lab Medicinelabmed.ascpjournals.org

doi: 10.1309/LMZNZ2Y1P3KRDQYL (2009) LabMedicine, 40, 728-731.

Changes of Serum Lactate Dehydrogenase and Potassium Levels Produced by a Pneumatic Tube System

Ming Cui, PhD1,

Rongrong Jing, PhD1 and

Huimin Wang, PhD1,2

+ Author Affiliations

1Center of Laboratory Medicine, Affiliated Hospital of Nantong University

2Public Health Institute of Nantong University, Nantong, Jiangsu Province, People's Republic of China

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Abstract

Objective: Errors in laboratory measurements could be derived from many pre-analytical factors. The aim of this study was to assess the influence of the hospital's pneumatic tube system (PTS) on serum lactate dehydrogenase (LDH) and potassium.

Methods: Forty-five healthy blood donors were involved. We studied LDH and potassium delivered to the laboratory by a PTS with different carrier inserts and transport times. In addition, influences of the PTS sending different types of specimens on LDH and potassium were determined.

Results: Blood specimens sent via PTS several times or without carrier inserts had statistical changes in LDH; the potassium had a slightly rising trend. Of the under-filled blood draw tubes or lithium heparin tube specimens, changes were caused by the PTS, but there were no effects on pure serum specimens.

Conclusions: Many minor shakings derived from the transportation of the PTS inevitably influenced LDH and potassium.

Rapid sample delivery systems, usually pneumatic tube systems (PTSs), have been installed in hospitals to transport blood specimens from the phlebotomy site to the core laboratory and deliver patient reports to clinicians. The use of such rapid sample delivery systems can significantly reduce the turnaround times (TATs) of results, which account for approximately 40% in the laboratory median TATs.1 However, the forces applied on a blood specimen transported by a PTS include sudden accelerations/decelerations, changes in air pressures, movement of blood in the test tube, and vibrations. It should be noted that the strong forces from the PTS can potentially affect some clinical laboratory measurements, such as blood gas measurements,2 spectrophotometric analysis of cerebrospinal fluid,3 routine and novel hematology, and coagulation analyzations.4 In some cases it will induce blood cell deterioration caused by rapid a ccelerations and decelerations along its trajectory.5 Thus, considering the blood specimen's quality, Sodi and colleagues stressed that all laboratories should investigate their blood specimen's susceptibility to hemolysis when transported through the PTS.6

The aim of this study was to evaluate the possible changes to the levels of 2 sensitive indicators, lactate dehydrogenase (LDH) and potassium. Both easily leak out of the blood cells in blood specimens when transported through the PTS in our hospital.

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Materials and Methods

Description of the PTS

The PTS (Sumetzberger, Vienna, Austria) installed in our hospital had 2 subsystems, 52 stations, a constant speed of 6 m/s, and the longest route of 600 m. In our present study, the test specimens were transported by the PTS from the phlebotomy site to the clinical chemistry laboratory, which is approximately 90 m including 17 vertical and horizontal bends (800 mm radius) and 2 switches. The carriers have a diameter of 160 mm and a length of 440 mm. Two kinds of carrier inserts (sponge-rubber and plastic-bag) were used for protection during the transportation in the PTS.

Specimens and Experimental Design

The study subjects consisted of 45 healthy blood donors (21 males and 24 females, mean age 29 years, range 22–35 years). All subjects gave informed consent to participate in the study. The collection of venous blood specimens was performed by a single venipuncture from the antecubital vein by trained phlebotomists. Two kinds of Vacuette blood collection tubes, 5 mL clot activator tubes and 4 mL lithium heparin tubes, were used in this study.

Part 1: Effects of r Inserts and Transport Times

A total of 50 mL of blood from each donor was collected into 10 Vacuette clot activator tubes. Of the 10 specimens, No. 1 was hand carried from the phlebotomy site to the clinical chemistry laboratory (mode H). Numbers 2, 3, and 4 were protected with sponge-rubber inserts (mode S) and transported by the PTS 1 time, 5 times, or 9 times, respectively. Numbers 5, 6, and 7 were protected with plastic-bag inserts (mode P) and sent via the PTS for the above times respectively. Numbers 8, 9, and 10 were transported with no inserts (mode N) by the PTS for the same times respectively.

Part 2: Effects of Transportation of Under-filled Blood Specimens and Anticoagulated Specimens

We obtained 10 mL of blood from each donor. The first 1 mL of blood was drawn into a 5 mL Vacuette clot activator tube, and only 20% of the tube capacity was filled. Another 5 mL Vacuette clot activator tube was filled with 5 mL of blood, and a 4 mL Vacuette lithium-heparin tube was simultaneously filled with 4 mL of blood. Then all 3 specimens were transported by the PTS 5 times with sponge-rubber inserts.

Part 3: Effects of Transportation of Serum

The amount of 7 mL of blood from each donor was drawn into 2 Vacuette clot activator tubes and allowed to clot for 30 minutes. Pooled sera from the 2 tubes were aliquotted into 3 Vacuette tubes after centrifugation. One of them was hand carried for 1 time; the others were transported by the PTS for 1 time or 9 times, respectively.

In each part of the study, a standardized procedure was followed to eliminate certain variables: all measurements of each part were tested in the same run; all blood specimens were routinely centrifuged for 10 minutes at 2,500 × g; hand carrying was always done by the same person.

Sample Analysis

Lactate dehydrogenase activity was measured on the Hitachi 7600 instrument (Hitachi, Tokyo, Japan) with an IFCC-recommended method. An ISE method was used for measuring potassium levels. The calibration was processed with Randox calibrators (Randox Laboratories, Crumlin, United Kingdom) in accordance with the manufacturer's instructions, and internal quality controls were performed in the same batch with these analytical specimens.

Statistical Analysis

All statistical analyses were used by SPSS 15.0 or Med-Calc 9.6 software. The paired t-test or one-way ANOVA and LSD analyses were used to evaluate the statistical differences among groups. P<0.05 was regarded as statistically significant.

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Results

Part 1: Effects of r Inserts and Transportation Times

To determine the effects of the PTS with different carrier inserts on the results of serum LDH and potassium, we compared specimens sent to the laboratory via a PTS with hand-carried specimens drawn from the same donors at the same time. Table 1 shows the statistically significant changes in LDH between specimens that were hand carried and those sent through the PTS with no carrier insert (mode N). Among the 3 modes (S, P, N), significant differences were found between mode N and modes S and P (P<0.001). For potassium, there were rising trends during the PTS transportation (Figure 1).

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Table 1 Summary of Statistical Data on Specimens Sent via PTS for Different Times in 4 Sending Modes

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Figure 1 Effect of transportation modes and times on the values of LDH and potassium. Mean LDH and potassium (±SD) are represented by the box; medians are plotted as a line inside the box; error bars represent the 10th and 90th percentiles. Means of each group are linked by a line. hc1, sent by hand 1 time; sr1, sr5, or sr9, sent via PTS with sponge-rubber inserts 1 time, 5 times, or 9 times respectively; pb1, pb5, or pb9, sent via PTS with plastic bag inserts 1 time, 5 times, or 9 times respectively; ni1, ni5, or ni9, sent via PTS without carrier inserts (no inserts) 1 time, 5 times, or 9 times respectively.

Table 1 also demonstrates the effects of transport times on results of serum LDH and potassium under modes S, P, and N. When the transport time increased, the levels of LDH were higher, and statistical changes were found (P<0.001). For potassium, there were rising trends between only 1 time and many times (Figure 1).

The PTS with no carrier insert and increased transportation affected the serum LDH and potassium, but the extent of changes was different.

Part 2: Effects of Transportation of Under-filled Blood Specimens and Anticoagulated Specimens

Table 2 and Figure 2 show the data of paired specimens when sending them via the PTS 5 times with sponge-rubber protection. For LDH and potassium, there were statistically significant changes in under-filled specimens compared to filled specimens (Pâ‰¤0.0001). In addition, under complete tube-filling circumstances, statistical differences were also found between clotted specimens and lithium-heparin anticoagulated ones (Pâ‰¤0.0001). However, LDH values were higher in anticoagulated tubes than in serum tubes while potassium was lower.

The underfilled or the unclotted specimens sent via PTS have an effect on the results of LDH and potassium. The levels of serum LDH were more altered by the PTS than potassium.

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Table 2 Analytical Results of 3 Kinds of Specimens When Sent via the PTS for 5 Times and Their Significance

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Figure 2 Effect of transportation specimen types on the values of LDH and potassium. When 1 mL of blood was drawn into a 5 mL vacuum tube and 4 mL remained, the levels of LDH and potassium were higher than the values of fully-filled specimens. However, in complete fully-filled circumstances, there was a higher value of LDH and a lower value of potassium in plasma than in serum.

Part 3: Effects of Transportation of Serum

When sera were sent by the PTS many times and by hand 1 time, no statistical changes of LDH and potassium were found (Table 3).

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Table 3 Summary of Statistical Data of Serum LDH and Potassium with 2 Sent Means for Different Times

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Discussion

Pneumatic tube systems allow rapid and convenient transport of blood specimens to clinical laboratories and are widely used in modern medical centers. However, there is growing attention to blood specimen quality affected by the PTS.

To the best of our knowledge, few studies have investigated the effect of PTS on hemolysis. In a study by Stair and colleagues,7 of the 291 specimens they studied, 47 of those carried by hand were visibly hemolyzed on arrival, compared with 40 specimens transported by a PTS. The hemolysis was determined by a technologist who was blinded to how the pair of specimens had been reported. There was no significant difference in hemolysis frequency between sent specimens by hand and via PTS. Fernandes and colleagues also reported there was no significant difference in the hemolysis rate between specimens delivered by a PTS and those delivered by a human courier. In their essays, hemolysis was measured by visual inspection of the specimens using a 4-point validated Likert scale based on the plasma hemoglobin concentration.8 However, in the Steige and colleagues study, hemoglobin, LDH, and potassium of the blood specimens would alter when sent through their PTS, which had some different characteristics when compared to our PTS, such as number of bends, carriers, inserts, and transport speeds.9

From the published studies, it is apparent that differences exist in different PTSs. Therefore, PTSs should be evaluated prior to use for transport of whole blood specimens. The aim of this study was to assess the influence of the PTS in our hospital on the levels of serum LDH and potassium that easily leak out of the blood cells.

The first part of the study showed protection played an important role in the specimens' transportation. Statistical differences existed between hand-carried blood speciments and those transported via the PTS without sponge-rubber or plastic-bag inserts for 1 time, statistical differences occurred compared to hand-carried ones. In addition, we found there were statistical changes between modes S, P, and N despite the number of times sent. These indicate blood specimens should be protected with carrier inserts during transportation by the PTS. Furthermore, with increased transportation, the rising LDH values showed the statistical difference under modes S, P, and N. All of these demonstrated that during the transportation of blood specimens, too many slight shakings had inevitably influenced the stability of some blood constituents.

In addition, blood specimens transported in incompletely filled tubes appeared to have been shaken more than those transported in completely filled tubes, which was consistent with findings by Harold and colleagues.9 Additionally, we found the PTS had more influence on anticoagulated blood specimens than completely clotted specimens. The anticoagulated blood specimens induced more increased LDH values than clotted specimens transported by the PTS. It has been well known the values of LDH are higher in serum tubes than in heparin ones when these tubes were transported by hand (the routine way). However, the extent of influence was different between LDH and potassium. The probable explanation of our results was that the concentration of red cell LDH was 160-fold greater than that present in the plasma10 or 150 times greater than that of normal serum. However, the distribution of intracellular and extracellular potassium is not as obvious as LDH (ie, the concentration of potassium inside the RBC was only 23 times as much as that found in plasma).10 The shakings induced by a PTS were so slight the changes of potassium were not similar to LDH, which was higher in heparin tubes than in serum ones after being transported by the PTS. No slight influence of PTS is more easily ignored than high value variables. Although a World Health Organization document recommended plasma specimens for the test of LDH and potassium, our results showed the changes of LDH and potassium in lithium-heparin tubes after sending via the PTS could not be ignored.11

In addition, we found there were no statistical changes when sera were transported several times through the PTS. This reminds us the transportation of serum is available. The whole blood specimen should be centrifuged after completed clotting, and the sera were aliquoted into another tube to be sent via the PTS.

In conclusion, although the use of a PTS increased work efficiency and decreased TATs, all clinical laboratory staff should recognize the negative side of PTS with regards to the stability of blood constituents.

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Acknowledgments

We gratefully acknowledge Jianyou Su, Lianying Chen, and Jianhui Xu of the Clinical Chemistry Laboratory Section and Yinchun Chen of the Blood Sampling Center for their skillful work.

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