Effect of the addition of the antioxidant taurine on the complete blood count of whole blood stored at room temperature and at 4ºC for up to 7 days

ORIGINAL ARTICLE

Effect of the addition of the antioxidant taurine on the complete blood count of whole blood stored at room temperature and at 4ºC for up to 7 days

Mahmoud Mohammed Sirdah^I; Abdelnasser Kassem Abushahla^I; Heba Abd Allah Al-Sarraj^II

^IAl Azhar University-Gaza, Gaza, Palestine

^IIPalestinian Ministry of Health, Gaza, Palestine

^{Corresponding author}

ABSTRACT

BACKGROUND: The complete blood count is one of the most common routine tests. This study aimed to evaluate possible effects of the antioxidant taurine on the complete blood count of whole blood stored at room temperature and at 4ºC over seven days.

METHODS: Venous blood samples of 25 healthy males were distributed into two sets of tubes with each set of four tubes containing 50 µL of solutions with zero, 2.5 g/L, 5 g/L, 10 g/L taurine. The tubes were kept at room temperature or at 4ºC. Complete blood counts were performed on seven successive days. The mean percentage changes [Δ = (mean value - mean baseline value) / mean baseline value x 100] were calculated and compared.

RESULTS: Complete blood count parameters exhibited different patterns of behavior which were affected by the storage temperature, time and taurine concentration. Taurine at room temperature significantly enhancedthe stability of: the platelet count over seven days (Δ7 at 2.5, 5 and 10 g/L taurine were 5.45, 6.11, and 5.80 x 10⁹ cells/L, respectively); the red blood cell count over five days (Δ5 at 2.5, 5 and 10 g/L taurine were 1.59, 2.79, and 1.98 x 10¹² cells/L, respectively); mean corpuscular hemoglobin over five days (Δ5 at 2.5, 5 and 10 g/L taurine were -0.91,-1.52 and -0.84 fl respectively); and red cell distribution width over two days (Δ2 at 2.5, 5 and 10 g/L taurine were 0.90%, 1.30% and -0.1%, respectively). No additional stabilizing effects of taurine were reported for the mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, hematocrit and hemoglobin, while it negatively affected the white blood cell stability.

CONCLUSION: Complete blood count parameters exhibited variable stability patterns in respect to temperature, time and taurine concentration.

Keywords: Blood preservation; Taurine/blood; Platelet count; Antioxidants; Cold temperature

Introduction

The complete blood count (CBC) is one of the most common routine laboratory tests requested as the first step to diagnose an illness or clinical presentation. With the development of automated hematological analyzers, the CBC has become an easy, quick, and reliable test that can give valuable information to physicians, leading to provisional diagnosis and to direct further testing. Currently, most clinical laboratories are equipped with modern automated analyzers that are capable of processing a large number of hematological tests in an efficient and timely manner^(1,2). However, for reliable results, it is essential that specimens are collected properly and in the right anticoagulant and then examined in a calibrated analyzer within a specified time frame according to the manufacturer instructions^(3-6).

The recent trends towards large centralized laboratories, and changes in laboratory organizations, have brought a new perspective to redistribution. Laboratories now test specimens that have been dispatched over long distances; as a result, testing is often delayed by 12-24 hours or more after venipuncture. Moreover, at weekends, this interval may exceed 36 hours. Therefore, when such specimens arrive in the laboratory, technicians must decide on whether to accept or refuse the processing of the specimens⁽⁶⁾. Although laboratories should maintain the consistency of results, disproportionate delays in processing might affect the reliability of results⁽⁷⁾.

Taurine (2-aminoethanesulfonic acid - NH₂CH₂CH₂SO₃H), which is a naturally-occurringß-sulfonated amino acid, is one of the most abundant free amino acids in the human body⁽⁸⁾; a 70 kg person can have up to 70 g of taurine⁽⁹⁾. Taurine has been demonstrated to function as a direct or indirect antioxidant, inhibiting lipid peroxidation, and stabilizing biomembrane structures and function by preventing any increase in membrane permeability due to the effect of oxidants, maintaining intracellular ion homeostasis, and inhibiting membrane protein phosphorylation^(8-10).

Different studies have revealed the stability of whole blood samples when stored at a low temperature or when certain anticoagulants are used^(2,5,11-13), however, to the best of our knowledge no published studies have investigated or considered the effect of antioxidants on the stability of CBC parameters. Therefore, due to the aforementioned effects of taurine, the present work was designed to evaluate any possible effects of the antioxidant taurine on the reliability of the CBC of whole blood specimens stored in vitro at room temperature and at 4ºC over seven days.

Methods

Sampling

After the approval of the study by both the Biology Department Council (BDC) and the Deanship of the Scientific Research Council (DSRC) of the Al-Azhar University, Gaza,apparently healthy nonsmoking male university students (18-20years old) were informed about the objectives and scope of the study and invited to participate. Twenty-five students freely accepted andall signed the consent form of the study thus accepting enrollment and the drawing of venous blood. The study was performed inaccordance with the ethical standards laid down in the 1964 and 1975 Declarations of Helsinki and the modifications of 1996.

Venous blood samples (20 mL each) were collected in K₃ethylenediaminetetraacetic acid (EDTA) tubes and distributed almost equally into two groups. One set of tubes was kept at the ambient room temperature (23 ± 2ºC) while the other set was kept refrigerated at 4ºC. Each set contained four K₃-EDTA tubes, and each tube represented a study subgroup. Therefore, four study subgroups (one control and three with different taurine concentrations) were included in each set for the present study.

For each set, CBC measurements [white blood cell (WBC),red blood cell (RBC), hemoglobin (Hb), hematocrit (Hct), meancorpuscular volume (MCV), mean corpuscular hemoglobin (MCH),mean corpuscular hemoglobin concentration (MCHC), red celldistribution width (RDW), and platelets (PLT)] were performed atthe time of collection and then daily for the following seven daysusing an Abbot CELL-DYN 1800 Sapphire Hematology Analyzer(Abbott Diagnostics, Santa Clara, CA, USA).

Study subgroups

The four subgroups at each storage temperature were as follows:

Subgroup I: 2.5 mL of venous blood was collected in K₃-EDTA and 50 µL of normal saline solution, no addition of taurine (Control Group).

Subgroup II: 2.5 mL of venous blood was collected in K₃-EDTA and 50 µL of 2.5 g/L taurine solution (five times the normal plasma taurine concentration⁽¹⁴⁾) was added.

Subgroup III: 2.5 ML of venous blood was collected in K3-EDTA and 50 µL of 5 g/L taurine solution (ten times the normal plasma taurine concentration) was added.

Subgroup IV: 2.5 mL of venous blood was collected in K3-EDTA and 50 µL of 10 g/L taurine solution (twenty times the normal plasma taurine concentration) was added.

Statistical analysis

The IBM SPSS program (version 17, IBM Corporation, Somers, NY) was used for all statistical analyses in the study. Comparisons between the mean values of the hematological parameters were made using the t-test. One-way analysis of variance (ANOVA) was used to compare the means of more than two groups. Any two-tailed p-value < 0.05 was considered to be statistically significant. In addition, for each parameter the mean percentage change (Δ_i = [mean value on day _i - mean baseline value] / mean baseline value x 100) was calculated and compared, where _i represents the day during the storage period.

Results

Baseline values and reliability of complete blood count parameters

There were no significant differences between the baseline means of all CBC parameters of samples stored at room temperature and at 4ºC either when compared to the control group or between different taurine subgroups (p-value > 0.05). The reliability of different CBC parameters was evaluated in terms of stability from baseline values. Non-significant differences or changes from baseline values indicate stability and hence reliability. Moreover, for each parameter the mean percentage change (Δ_i) was calculated over the seven days compared to baseline values, which could be used to describe the level of precision of the readings compared to baseline values. So, when a precision level of 5% is acceptable this is reflected by Δ_i < ± 5%.

Platelet count and mean platelet volume

The PLT count changed significantly and was affected by storage temperature and time (Table 1). However, storage with taurine at room temperature considerably enhanced the stability of the PLT count over seven days, with no significant differences compared to the baseline. In terms of mean percentage changes, all the values were within ± 10% except for the seventh day (10.96%). While storage of blood in taurine at 4ºC showed no remarkable effect toward the stability of the PLT count.

Neither storage temperature nor the addition of taurine at the different concentrations stabilized mean platelet volume (MPV). The ANOVA statistical test showed significant changes of MPV over the seven days of storage, with a trend towards an increase in MPV. The mean percentage change in MPV increased considerably with time and by the seventh day it reached values of 24.97% and 28.60% at room temperature and at 4ºC, respectively.

Red blood cell count and related indices

Table 2 illustrates the instability of the RBC count over time with significantly different values from baseline (p-value < 0.05). However taurine at 10 g/L tends to exert some stabilizing effect at room temperature over the first five days of storage. While the mean percentage changes in the RBC count at day seven were almost 3% and 2.2% at room temperature and at 4ºC, respectively, with the addition of 2.5 g/L taurine these mean changes reduced to 1.59% and 1.17%, respectively.

At all investigated concentrations, taurine did not enhance the stability of MCV at room temperature or at 4ºC. The MCV was stable for two days both at room temperature and at 4ºC (Table 3). However mean percentage changes of MCV increased over time but these changes were lower at 4ºC with a value of about 10% by day seven compared to 14.31% at room temperature.

MCH values were found to be unstable over the seven days both at room temperature and at 4ºC (Table 4). However the addition of taurine increased the stability of MCH at both temperatures. Mean percentage changes in MCH were very small with a maximum change of 2.25%.

Additionally, MCHC values were not stable at both temperatures even with the addition of taurine. The values of MCHC decreased significantly with time. However, mean changes in MCHC values were less than 10% for four days at room temperature and for six days at 4ºC without showing any significant effect of taurine.

Hct at room temperature and at 4ºC showed significant increases over the seven days of storage. Taurine did not stabilize Hct at both temperatures, however, the mean percentage changes in Hct values were less than 10% over four days at room temperature and over six days at 4ºC, whether taurine was added or not.

The Hb concentration remained stable over the seven days of storage compared to baseline values at room temperature and at 4ºC, and thus there was no advantage on the stability of Hb with the addition of taurine (Table 5). The mean percentage change was almost 1% in the Hb concentration over the seven days without any significant effect of taurine.

At room temperature, the RDW changed significantly over time starting from the second day. However, taurine at the different concentrations stabilized RDW readings for two days after which taurine had no stabilizing effect and all RDW readings after the second day were significantly different from the baseline values. While at 4ºC, the RDW values were stable for two days with and without taurine. Moreover, storage with taurine at 5 g/L enhanced the stability of RDW value for an additional 24 hours. The mean changes in RDW were less than 10% at room temperature for the first three days and less than 10% at 4ºC for 5 days.

White blood cell count

WBC count was stable with non-significant changes from the baseline value when preserved at room temperature over seven days (Table 6). The addition of taurine at 2.5 g/L did not alter the stability, however, increasing the concentration of taurine to 5 and 10 g/L, negatively affected the stability of WBC counts. On the other hand, at 4ºC the WBC counts were stable only for four days compared to baseline values. The changes in the WBC counts at room temperature were less than 4% over the seven days, while the changes reached almost 20% when the sample was kept at 4ºC.

Discussion

The CBC or hemogram is a routine laboratory test The CBC or hemogram is a routine laboratory test that evaluates number, size, morphology and related indices of the blood: RBC, WBC, and PLT. Significant time-and temperature-dependent morphological changes can occur with the prolonged storage of blood^{(6,7,13,15,16)}. The CBC as well as blood smears should be processed as quickly as possible after collection to avoid normal degenerative changes in blood cell morphology, which are mainly due to weakness in controlling cell membrane integrity, and consequently changing cell volume and related indices. Most importantly, blood cells can rupture after swelling⁽¹⁷⁾. Different studies have been performed to evaluate the effect of storage time and temperature on the stability of CBC parameters and indices. Most of such studies define stability in terms of mean percentage changes and authors usually considered parameters stable when the mean percentage change is within 5% of baseline values^(7,15,16,18). However, other studies defined stability differently and used the ANOVA or t-test to identify significant differences compared to baseline values over the study period^(13,19,20). In the current work both approaches were used and presented, however, parameters or indices were considered stable when there were no significant differences in the mean values compared to baseline values according to the ANOVA or t-test. Furthermore, it is worth mentioning that none of the published studies investigated the effect of antioxidants on the stability of CBC parameters. Thus, to our best knowledge, this work may be considered the first work where the possible effects of antioxidants are investigated and discussed.

Baseline values were not significantly different between the two sets of tubes and subgroups which shows the homogeneity of the data. It is worth mentioning that all investigated blood samples were drawn from apparently healthy never-smoker males which minimizes any interfering or confounding factors related to physiological and hematological differences between males and females and also between smokers and nonsmokers⁽²¹⁾.

The PLT count was found to be considerably changed over time with no stabilizing effect of storage temperature. These changes could be attributed to alterations in PLT morphology, movement and aggregation during storage⁽¹³⁾. However, taurine significantly enhanced PLT stability at room temperature, but not at 4ºC where fluctuating and dissentious stabilities are observed. Therefore, for the PLT count, the preservation of samples at room temperature with taurine, even at low concentrations such as 2.5 g/L, could enhance stability and provide reliable results for at least seven days. The instability of the PLT count over time, whether kept at room temperature or refrigerated at 4ºC, are concomitant to the findings of other works^(15,16,20) although one study in 2008 reported a better stability of the PLT count at room temperature⁽¹⁸⁾. These stabilizing effects of taurine on the PLT count may be attributed to different mechanisms including the stabilization of the PLT membrane, re-supplementing PLT with taurine in vitro⁽⁹⁾, an antithrombotic effect^(22,23) and decreased PLT aggregation⁽²⁴⁾.

The RBC count was found to be instable over time as indicated by the significant differences between means. While, when defining stability in terms of mean percentage changes, the RBC count could be considered stable within a precision of ± 5%, which is comparable to the findings of other researchers^(7,16,18). The stabilizing effect of taurine on RBC might be attributed to its antioxidant role by scavenging free radicals that stimulate membrane lipid peroxidation and hence stabilize the RBC membrane^(7,9,10). Therefore, the addition of taurine could be suggested for late-arriving EDTA blood samples when the evaluation of RBC count is of central importance.

Although, taurine was found to exert stabilizing effects on PLT and RBC counts, it did not stabilize the mean volumes of these blood components, the MPV and MCV, respectively, as have been observed elsewhere^(6,7,15,16). This may be attributed to the preservation of structural integrity of their membranes by taurine but not the functional transport across the membrane which seems to be independent of the action of taurine.

It is worth mentioning that the addition of taurine was found to exert some stability on the MCH values both at room temperature and at 4ºC for five and four days, respectively, but at different concentrations. The instability of MCHC values at different temperatures and despite the addition of taurine may be attributed to the increasing MCV over time and consequently increases in Hct which is the denominator for calculating MCHC. On the other hand, hemoglobin concentration was found to be stable over the seven days of the study at both temperatures, which is concomitant to other findings^(7,16,19). Storage with taurine did not enhance hemoglobin stability. Therefore, hemoglobin concentration can be considered reliable for one week whether the blood is kept at room temperature or at 4ºC. Effectively, taurine exerted a stabilizing function on the RDW values both at room temperature and at 4ºC. However, it exerted a negative effect on the stability of the WBC count, therefore, WBC counts of blood preserved in EDTA at room temperature without taurine are more reliable as these conditions will provide laboratories with reliable results for seven days.

Hematological changes of whole blood collected for diagnosisand for transfusion purposes may be co-related. Therefore, werecommend that other researchers investigate the addition oftaurine together with anticoagulant-preservative solutions suchas acid-citrate-dextrose (ACD) and citrate phosphate dextroseadenine (CPDA-1) on the physiological and biochemical propertiesof whole blood used for transfusion purposes. We expect promisingeffects of taurine due to its many important and beneficial effectsand safety in the human body and on aforementioned cells.

Conclusion

The different CBC parameters and their related indicesexhibited variable stability patterns according to storagetemperature, time of storage and the addition of taurine.Some parameters and indices are more stable at 4ºC than at room temperature (RDW, RBC), one is more stable at roomtemperature than at 4ºC (WBC), and others exhibited differentlevels of stability at the different temperatures (MCV, Hb).Several are limited or unstable at any temperature over time(PLT, MPV, MCH, MCHC, Hct) while for some, the stabilitycould be partially or totally enhanced by the addition of taurine(PLT, RDW, MCH).

Submitted: 10/5/2012

Accepted: 11/4/2012

Conflict-of-interest disclosure: The authors declare no competing financial interest

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Publication Dates

• Publication in this collection
  05 Apr 2013
• Date of issue
  2013

History

• Received
  05 Oct 2012
• Accepted
  04 Nov 2012