Stability of therapeutic drug measurement in specimens collected in VACUTAINER plastic blood-collection tubes

Adsorption of Therapeutic and Recreational Drugs During Prolonged Storage of Plasma Samples in Gel Separator Tubes

Hospital samples collected in gel separator tubes are often submitted to forensic toxicology laboratories for analysis in impaired driving and death investigations. Drug adsorption to the gel separator material may lead to underestimation of the drug concentration present at the time of sample collection, potentially affecting the interpretation of analytical results. Using liquid chromatography--tandem mass spectrometry (LC--MS-MS), decreases in plasma concentration of 53 drugs and metabolites relevant to forensic toxicology casework were investigated in samples stored in BD Vacutainer® PSTTM tubes for up to 3 months. After storage for only 1 day, approximately 50% of the drugs and metabolites had significantly lower concentrations in plasma separation tubes (PSTs) compared to non-gel tubes (up to 27% lower). After storage for 3 months, approximately 75% of the drugs and metabolites had significantly lower concentrations in PSTs compared to non-gel tubes (up to 69% lower). Fentanyl, carfentanil, ketamine, diphenhydramine and several antidepressants were among the drugs most susceptible to adsorption. Central nervous system stimulants (e.g., methamphetamine and amphetamine) as well as naturally-occurring and semi-synthetic opioids (e.g., morphine, hydromorphone and oxycodone) were among the drugs least susceptible to adsorption and displayed only minimal relative decreases in concentration (if any) over the 3-month sample storage period. The potential for decreases in drug concentration due to adsorption of drugs to the gel material should be considered for toxicological interpretation based on the analysis of a sample collected in a gel separator tube.

Evaluation of Serum and Rapid Serum Separator Collection Tubes for Therapeutic Drug Assays

Appropriate specimen collection and storage is essential to preserve sample integrity and ensure accurate test results. The default collection containers for blood drug concentrations are tubes without gel separators to avoid possible drug adsorption. However, routine chemistry tests are generally collected in gel separator tubes due to their convenient transport and processing; collection of an additional gel-free tube is often required for drug measurements. Citrated whole blood was pooled, spiked with drug, and transferred to three tubes (red, SST gold, RST orange) containing calcium chloride. Blood was allowed to clot, centrifuged and stored at ambient temperature (24 h) or refrigerated (7 days). At defined times, serum drug concentrations were determined (Roche cobas c502). Based on these results, specimen collection requirements were updated to allow serum separator tubes for 17 assays. Of the 21 assays evaluated, 18 displayed acceptable stability in both gel-containing tubes (acetaminophen, amikacin, carbamazepine, digoxin, ethanol, gentamicin, lamotrigine, levetiracetam, lithium, methotrexate, phenobarbital, phenytoin, salicylate, theophylline, tobramycin, valproic acid, vancomycin, voriconazole). Three drugs displayed strong decreases in measured concentrations after storage in one or both gel-containing tubes (total tricyclics, lidocaine, and free phenytoin). Following adoption of gel-containing tubes, 94% of the five most frequently ordered drug monitoring tests in the Emergency Department were collected in serum separator tubes. Evaluation of the stability and accuracy of commonly monitored drugs revealed that the majority were not affected by exposure to gel separator material under conditions similar to outpatient clinic storage, courier transport and laboratory storage. Expanding the collection requirements for appropriate drugs to include gel separator tubes decreases the number of specimens drawn and the complexity of laboratory workflows.

A comparative study on the effect of blood collection tubes on stress oxidative markers

Oxidative stress has a major role in disease pathogenesis. However, limited studies have investigated the effect of various sample collection tubes on oxidative biomarkers. The present study aimed to evaluate the effect of different collection tubes on the variation of malondialdehyde (MDA), nitric oxide (NO), total thiol (t-SH), and ferric reducing ability of plasma (FRAP) levels. A total of 35 individuals participated in this study and each collected sample was separated into three different tubes: glass tubes (GTs), plain plastic tubes (PTs), and gel separator tubes (GSTs). The results of PTs and GSTs were compared to those of GTs as the reference tube. The comparison between the means of biomarkers in various tubes indicated that there was no significant difference in MDA results between tubes. In contrast, t-SH and NO content were significantly decreased in GSTs and PTs compared to GTs. However, the Bland-Altman analysis showed an acceptable concordance for the mentioned analytes and the statistically significant differences were not clinically significant for NO, MDA, and t-SH antioxidant parameters. Moreover, the FRAP level was considerably lower in GSTs compared to GTs. Nevertheless, the Bland-Altman analysis showed a high bias percentage for the FRAP assay when using PTs and GSTs. According to the present results, it can be concluded that switching to plastic blood collection tubes or serum separation tubes could influence the FRAP results. However, there was no interference for the interpretation of other antioxidant assays in different types of collection tubes. Hence, it is suggested to use GTs for total antioxidant capacity evaluations, especially the FRAP assay.

A Multicenter Evaluation of a Nongel Mechanical Separator Plasma Blood Collection Tube for Testing of Selected Therapeutic Drugs

BACKGROUND

Some therapeutic drugs are unstable during sample storage in gel tubes. BD Vacutainer® Barricor™ Plasma Blood Collection Tube with nongel separator was compared with plasma gel tubes, BD Vacutainer PST™, PST II, and BD Vacutainer Serum Tube for acetaminophen, salicylate, digoxin, carbamazepine, phenytoin, valproic acid, and vancomycin during sample storage for up to 7 days.

METHODS

Seven hospital sites enrolled 705 participants who were taking at least one selected drug. The study tubes were collected and tested at initial time (0 h), after 48 h of storage at room temperature and on day 7 (after additional 5 days of refrigerated storage). The performance of BD Barricor tube was evaluated for each drug by comparing BD Barricor samples with samples from the other tubes at 0 h from the same participant; stability was evaluated by comparing test results from the same tube at 0 h, 48 h, and 7 days.

RESULTS

At 0 h, BD Barricor showed clinically equivalent results for selected therapeutic drugs compared with the other tubes, except phenytoin in BD PST. Phenytoin samples ≥20 µg/mL in BD PST had 10-12% lower values than samples in BD Barricor. During sample storage, all selected drugs remained stable for 7 days in BD Barricor and in serum aliquots. In BD PST, all drugs remained stable except phenytoin and carbamazepine and in BD PST II except for phenytoin.

CONCLUSION

The BD Barricor Tube is effective for the collection and storage of plasma blood samples for therapeutic drug monitoring without sample aliquoting.

Comparison of the effect of gel used in two different serum separator tubes for thyroid function tests

BACKGROUND

Selection and verification of blood collection tubes is an important preanalytical issue in clinical laboratories. Today, gel tubes are commonly used with many advantages, although they are known to cause interference in immunoassay methods. In this study, we aimed to compare SSTs of two different suppliers (Ayset clot activator & Gel and Becton Dickinson (BD) Vacutainer SST II advance) with reference tubes and evaluate the effect of storage time in terms of commonly used endocrine tests such as thyroid-stimulating hormone (TSH), free thyroxine (fT4), and free triiodothyronine (fT3).

METHODS

Fifty-five volunteers were included in the study. Samples were taken into three different tubes and analyzed for serum TSH, fT4, and fT3 on Architect ci8200 Immunoassay System. Clinical decision levels were estimated using total allowable error (TEa).

RESULTS

No difference was found between tubes in terms of TSH, fT3, and fT4 levels. From a statistical standpoint, TSH and fT4 levels were no longer stable during 24, 48, and 72 hours storage time periods. However, their variations were not clinically significant.

CONCLUSION

Ayset clot activator & Gel tubes and BD Vacutainer SST II advance tubes have comparable results with glass tube in terms of TSH, fT3, and fT4 levels on Architect ci8200 Immunoassay Systems. From a clinical standpoint, serum TSH, fT4, and fT3 concentrations may be considered as stable when storing these tubes over 72 hours.

Comparison of Improvacuter™ tubes with BD Vacutainer™ tubes for various hormones in the aspects of stability and influence of gel separators

Validation of blood collection tubes are important to determine the role of different collection tubes which influence the assurance of laboratory results. We compared two different tubes (Improvacuter

We compared the results of nine immunoassays performed on UniCel

Estradiol and testosterone concentrations obtained from Improvacuter Gel and Clot Activator tubes and BD Vacutainer SST II Advance tubes remained below the lower limits of analytical range for the same analytes while they were within the limits in BD Vacutainer Clot Activator tubes and Improvacuter tubes. Statistical significance of stability was not clinically significant for the hormone parameters we tested in all four tubes.

Gel containing tubes (both BD and Improve) gave comparable results with the tubes which do not contain gel except for estradiol and testosterone. The use of gel containing tubes for estradiol and testosterone are not recommended on UniCel

Suitability of Becton Dickinson Vacutainer rapid serum tube for collecting and storing blood samples for antibiotic and anticonvulsant drug monitoring

Aims

To investigate the suitability of newly developed Becton Dickinson Vacutainer rapid serum tube (RST) for therapeutic drug monitoring of antibiotics and anticonvulsants.

Methods

Two pools of citrated whole blood were created by spiking high and low concentrations of gentamicin, vancomycin, phenytoin, lamotrigine and carbamazepine. After recalcification with 15 mmol/L calcium chloride, spiked whole blood was added into four different Becton Dickinson blood collection tubes: RST, serum separator tube, red top tube and polyethylene plain tube. Serum aliquots were collected at baseline (0 h), 2 h, 24 h, day 3 and day 7. Drug concentrations were measured in batch by HPLC and the Architect c8000.

Results

Gentamicin and vancomycin concentrations were stable up to 7 days in all 4 blood collection tubes. Anticonvulsants results for the RST were stable and did not deviate substantially from those of the red top and plain tubes, and demonstrated better performance than the serum separator tubes that showed significant (≥10% bias, p<0.05) decrease in phenytoin and carbamazepine levels after 3 days of storage.

Conclusions

The RST provides acceptable drug stability over the course of 7 days for gentamicin, vancomycin, phenytoin and lamotrigine and over 3 days for carbamazepine.

Impact of blood collection devices on clinical chemistry assays

Blood collection devices interact with blood to alter blood composition, serum, or plasma fractions and in some cases adversely affect laboratory tests. Vascular access devices may release coating substances and exert shear forces that lyse cells. Blood-dissolving tube additives can affect blood constituent stability and analytical systems. Blood tube stoppers, stopper lubricants, tube walls, surfactants, clot activators, and separator gels may add materials, adsorb blood components, or interact with protein and cellular components. Thus, collection devices can be a major source of preanalytical error in laboratory testing. Device manufacturers, laboratory test vendors, and clinical laboratory personnel must understand these interactions as potential sources of error during preanalytical laboratory testing. Although the effects of endogenous blood substances have received attention, the effects of exogenous substances on assay results have not been well described. This review will identify sources of exogenous substances in blood specimens and propose methods to minimize their impact on clinical chemistry assays.

[Recommendations for antibiotic monitoring in ICU patients]

Monitoring plasma concentrations of antimicrobial agents used to treat infection in critically ill patients is one of the recommended strategies for improving clinical outcome. Drug monitoring has a double aim: to limit adverse events and to increase the effectiveness of the drugs. In clinical practice, however, this approach is mainly limited to monitoring plasma concentrations of vancomycin and aminoglycosides, although future extension to other antimicrobial agents would be desirable. Application of this technique varies considerably between hospitals, and this makes interpretation and comparison of the results obtained difficult. For this reason, representatives of various scientific societies related to the pharmacokinetic area have developed a series of recommendations for monitoring plasma concentrations of antimicrobials using vancomycin and several aminoglycosides as the reference. The recommendations are based on 14 questions encompassing all steps of the process: indication for the test, blood sampling (timing of blood collection, blood volume, tubes), transport to the laboratory, techniques applied, normal values, dose adjustment, and reporting the results. The purpose of these guidelines is to develop a process of monitoring plasma antimicrobial concentrations that is as homogeneous as possible to facilitate the design of multicenter studies, as well as the interpretation and comparison of results.

[Recommendations for antibiotic monitoring in ICU patients]

Monitoring plasma concentrations of antimicrobial agents used to treat infection in critically ill patients is one of the recommended strategies for improving clinical outcome. Drug monitoring has a double

AIM

to limit adverse events and to increase the effectiveness of the drugs. In clinical practice, however, this approach is mainly limited to monitoring plasma concentrations of vancomycin and aminoglycosides, although future extension to other antimicrobial agents would be desirable. Application of this technique varies considerably between hospitals, and this makes interpretation and comparison of the results obtained difficult. For this reason, representatives of various scientific societies related to the pharmacokinetic area have developed a series of recommendations for monitoring plasma concentrations of antimicrobials using vancomycin and several aminoglycosides as the reference. The recommendations are based on 14 questions encompassing all steps of the process: indication for the test, blood sampling (timing of blood collection, blood volume, tubes), transport to the laboratory, techniques applied, normal values, dose adjustment, and reporting the

RESULTS

The purpose of these guidelines is to develop a process of monitoring plasma antimicrobial concentrations that is as homogeneous as possible to facilitate the design of multicenter studies, as well as the interpretation and comparison of results.

Effect of blood collection tubes on total triiodothyronine and other laboratory assays

BACKGROUND

Increased total triiodothyronine (TT(3)) assay results in apparently euthyroid patients triggered an investigation of the effect of blood collection tubes on serum TT(3) and other laboratory assays.

METHODS

We examined potential assay interference for three types of tubes: plastic Greiner Bio-One Vacuette; glass Becton Dickinson (BD) Vacutainer; and plastic BD Vacutainer SST tubes. Serum samples from apparently healthy volunteers (age range, 30-60 years; 15 males and 34 females) were collected in different tube types and analyzed in 17 immunoassays (n = 49), 30 clinical chemistry tests (n = 20), and 33 immunology assays (n = 15). Tube effects were also examined by adding pooled serum to different tube types.

RESULTS

TT(3) values, when measured by the IMMULITE 2000 but not the AxSYM analyzer, were significantly higher (P <0.0001) for SST (2.81 nmol/L) than either glass (2.15 nmol/L) or Vacuette (2.24 nmol/L) tubes. The effect was large enough to substantially shift the distribution of patient values, increasing the percentage of values above the reference interval from 11.3% to 35.8%. The degree of interference from SST tubes on TT(3) differed among various tube lots and could be attributed to a tube additive shared by other plastic tubes. Results from several other tests statistically differed among tube types, but differences were not considered to be clinically significant.

CONCLUSIONS

Assay interferences from blood collection tubes represent challenges to clinical laboratories because they are not detected by the usual quality-control or proficiency testing programs. Laboratories can, however, address this problem by monitoring distribution of patients' results.

Evaluation of fluorescence polarization assays for measuring valproic acid, phenytoin, carbamazepine and phenobarbital in serum

The authors evaluated the fluorescence polarization (FP) assay on the COBAS INTEGRA 700 using COBAS INTEGRA reagent system cassettes for estimating the antiepileptic drugs valproic acid, phenytoin, carbamazepine, and phenobarbital in serum. The study comprised the determination of precision, method comparison performed against a conventional HPLC assay and linearity studies, according to the National Committee for Clinical Laboratory Standards (NCCLS) protocols. Precision results were well acceptable for all FP assays. Intra-assay coefficients of variation (CVs) were from 1.3% to 2.4% for valproic acid, from 0.8% to 2.8% for phenytoin, from 1.7% to 3.3% for carbamazepine, and from 1.3% to 2.3% for phenobarbital. Interassay CVs for these drugs ranged from 1.5% to 2.6%, from 2.9% to 6.5%, from 1.8% to 3.7% and from 1.5% to 3.2%, respectively. Results of the FP assays showed excellent correlation with those from HPLC: r = 0.99 for valproic acid, r = 0.98 for phenytoin, r = 0.98 for carbamazepine and r = 0.99 for phenobarbital. Linearity was satisfactory, with all CVs below the acceptable level. With the COBAS INTEGRA 700 analyzer FP assays are fully automated, which is less laborious and saves time compared with HPLC. Moreover, the fast measuring procedure is convenient in short turnaround time (STAT) analysis. It is an analytically reliable and rapid system, which can be used successfully for the therapeutic monitoring of antiepileptic drugs in serum.

Determination of antiepileptic drugs in biological material

Current analytical methodologies applied to the determination of antiepileptic drugs in biological material are reviewed. The role of chromatographic techniques is emphasized. Special attention is focused on new chemical entities as well as current trends such as high-speed liquid chromatographic techniques, hyphenated techniques and electrochromatography techniques. A review with 542 references.

Stability of Therapeutic Drugs in Serum Collected in Vacutainer Serum Separator Tubes Containing a New Gel (SST II)

The stability of therapeutic drugs in sera collected in Becton-Dickinson Vacutainer serum separator SST tubes has been well studied. Although most therapeutic drugs are stable, certain drugs such as phenytoin, carbamazepine, and phenobarbital decrease in concentrations over a long storage time. To circumvent this problem, Becton-Dickinson devised a new gel formulation. The authors studied the stability of 14 commonly monitored drugs in sera when stored on the new gel of the SST II tubes and compared the concentrations of drugs in sera stored in plain tubes (no gel), those stored in the old SST tubes, and those stored in the SST II tubes containing a new serum separator gel. The concentrations of most drugs studied did not decline even after 24 hours of storage in SST II tubes. After storage for 7 days in SST II tubes, the concentration of carbamazepine declined by 10% and that of phenytoin decreased by 4%. This is a significant improvement over the existing tube, where concentrations of several drugs declined with prolonged storage. The authors conclude that new SST II tubes are effective in collecting blood for therapeutic drug monitoring.

Time-dependent absorption of therapeutic drugs by the gel of the Greiner Vacuette blood collection tube

Stability of therapeutic drugs in sera collected in Becton-Dickinson VACUTAINER serum separator SST tubes has been well studied. Recently, the Greiner Vacuette serum separator tube has become available for blood collection. However, stability of therapeutic drugs in sera when the specimen is collected in the Greiner tube has not been reported. The authors studied the stability of 15 commonly monitored drugs in sera when stored on the gel of the Greiner serum separator tubes. The drugs studied were amikacin, gentamycin, tobramycin, vancomycin, digoxin, quinidine, theophylline, carbamazepine, phenobarbital, phenytoin, valproic acid, tricyclic antidepressants, salicylate, acetaminophen, and ethanol. The authors compared the concentrations of drugs in sera stored in plain tubes (no gel) and in sera stored in the Greiner tubes containing serum separator gel. They observed a significant decline in the concentrations of tricyclic antidepressants when stored in the Greiner tubes. Interestingly, concentrations of amitriptyline declined more than its metabolite nortriptyline and concentration of imipramine also decreased more than its metabolite desipramine. The concentration of carbamazepine also decreased slightly over time when serum was stored in the Greiner tube. Although declines in carbamazepine concentrations on prolonged storage in the Greiner tubes were statistically significant, the decreases may not be clinically significant. The concentrations of the other drugs studied did not decline when stored in the Greiner tubes. The authors conclude that the Greiner brand tube is not suitable for blood collection for analysis of tricyclic antidepressants.

Suitability of collection tubes with separator gels for collecting and storing blood samples for therapeutic drug monitoring (TDM)

In this study, we present significant changes occurring in serum drug concentrations while using blood collection tubes that contain a barrier gel. This report also contains results with antidepressant drugs, which have not been studied before with human samples. The drug concentrations were measured either with high performance liquid chromatography (HPLC) or fluorescence polarization immunoassay (FPIA). The results show that gel tubes are suitable for blood collection for antiepileptic, antibiotic, asthma and cardioactive drug measurements, since only slight adsorption was seen (0-5%). However, the studied tubes are not suitable for blood collection of antidepressants nor benzodiazepines, because the adsorption can be 5-30%. The adsorption was even higher (up to 40%) when samples were stored for 24 h after centrifugation in gel tubes. When the centrifugation step was performed after storage the effect of the barrier gel was lower (only 0-13%). Antidepressant drug measurements performed from patient specimens collected in the studied gel tubes and stored for 3 h showed <10% adsorption of the studied drugs. After 24 h storage time, concentrations of all analysed drugs decreased even more: adsorbed amount of drugs were about 5-20%. The studied gel tubes are proposed to be satisfactory for blood collection for antidepressant drug measurements if separation step is performed within 3 h after blood clotting. With the spiked samples the adsorption to barrier gel was higher, so it seems that adsorption is faster when drugs are not highly bound to serum proteins.

Effect of heating human sera at a temperature necessary to deactivate human immunodeficiency virus on measurement of free phenytoin, free valproic acid, and free carbamazepine concentrations

Minimizing the risk for infection to laboratory staff from a contaminated blood sample is a major safety goal in the clinical laboratory. One dangerous pathogen, the human immunodeficiency virus (HIV), can be deactivated by heating sera at 56 degrees C for 30 minutes. The authors previously reported that if serum was subjected to those conditions, the concentrations of the nine most commonly monitored drugs were not altered, whereas phenytoin and carbamazepine concentrations were reduced slightly. Monitoring free phenytoin, free valproic acid, and free carbamazepine concentrations is strongly recommended for patients with uremia, liver disease, and hypoalbuminemia. Because drug protein binding can be affected by temperature, the authors investigated the effect on free drug concentrations of sera heated to levels necessary for deactivation of the HIV virus. They measured total and free drug concentrations in serum pools prepared from patients receiving phenytoin, valproic acid, and carbamazepine. Serum pools were heated at 56 degrees C for 30 minutes and then brought to room temperature. The total and free drug concentrations were measured immediately after heating and then at 20- and 45-minute intervals. The concentrations of free phenytoin and free valproic acid were significantly higher after heat treatment. However, after equilibration of sera at room temperature for 20 minutes, the free concentrations of phenytoin were comparable to preheating values, although total phenytoin concentrations (Serum Separator Tubes) were reduced slightly. In contrast, free valproic acid concentrations did not return to the original levels even after 45 minutes. Free carbamazepine concentrations did not change even immediately after heating. However, total carbamazepine concentrations were reduced slightly when sera were heated in serum separator tubes (SST Tubes).

Standards of laboratory practice: cardiac drug monitoring

In this Standard of Laboratory Practice we recommend guidelines for therapeutic monitoring of cardiac drugs. Cardiac drugs are primarily used for treatment of angina, arrhythmias, and congestive heart failure. Digoxin, used in congestive heart failure, is widely prescribed and therapeutically monitored. Monitoring and use of antiarrhythmics such as disopyramide and lidocaine have been steadily declining. Immunoassay techniques are currently the most popular methods for measuring cardiac drugs. Several reasons make measurement of cardiac drugs in serum important: their narrow therapeutic index, similarity in clinical complications and presentation of under- and overmedicated patients, need for dosage adjustments, and confirmation of patient compliance. Monitoring may also be necessary in other circumstances, such as assessment of acetylator phenotypes. We present recommendations for measuring digoxin, quinidine, procainamide (and N-acetylprocainamide), lidocaine, and flecainide. We discuss guidelines for measuring unbound digoxin in the presence of an antidote (Fab fragments), for characterizing the impact of digoxin-like immunoreactive factor (DLIF) and other cross-reactants on immunoassays, and for monitoring the unbound (free fraction) of drugs that bind to α1-acid glycoprotein. We also discuss logistic, clinical, hospital, and laboratory practice guidelines needed for implementation of a successful therapeutic drug monitoring service for cardiac drugs.

Laboratory guidelines for monitoring of antimicrobial drugs

Few antimicrobial drugs meet the requirements for therapeutic drug monitoring. Those that are monitored include the aminoglycosides (gentamicin, tobramycin, and amikacin), chloramphenicol, and in some cases, vancomycin. For these drugs, there is evidence of a relationship between serum concentration, efficacy, and/or the incidence of adverse or toxic events. Monitoring begins with the appropriate timing of collection and continues through the analytical process to the integration of all data used to guide the clinician’s next decision.