Serum Separator Tubes Research Articles

Direct Detection of Methicillin-ResistantStaphylococcus aureusfrom Blood Cultures Using Three Non-Molecular Methods: PBP2a Latex Agglutination, PBP2a Rapid Immunochromatographic Assay and MRSA-Chromogenic Medium

Background: This study compared three non-molecular methods for the detection of methicillin-resistance directly from blood cultures containing Staphylococcus aureus: penicillin-binding protein (PBP) 2a latex agglutination (LA), PBP2a immunochromatographic assay (ICA) and MRSA chromogenic medium (CM). Methods: Fifty methicillin-resistant S. aureus (MRSA) and 50 methicillin-susceptible S. aureus (MSSA) were seeded into blood-culture bottles. When isolates returned a positive signal, 5 mL of culture was added to serum separator tubes and centrifuged at 1,300 g for 10 min. The pellets were then used as the inoculum for the PBP2a LA, MRSA-CM and PBP2a ICA. The pure colony was used for PBP2a LA test, additionally. Results: The respective sensitivities and specificities were 98 and 100% for PBP2a ICA, and 100 and 100% for MRSA-CM in direct detection of MRSA from positive blood culture. The results of PBP2a LA test using pure colony were entirely compatible with those by mecA gene PCR but the PBP2a LA test using the pellets directly isolated from positive blood culture showed sometimes ambiguous agglutination; its sensitivity and specificity were 78 and 100%, if ambiguous results were scored as negative, and were 90 and 92%, if ambiguous results were scored as positive, respectively. Conclusion: For direct detection of MRSA in positive blood culture, MRSA-CM and PBP2a ICA provided excellent results. The PBP2a LA test using pure colony also gave excellent results but the PBP2a LA test by the direct method using pellet of positive blood culture was slightly less sensitive than the other two methods. (Korean J Clin Microbiol 2012;15:27-31)

Biologic Variation of a Novel Cardiac Troponin I Assay

To the Editor: Cardiac troponin is the marker of choice for evaluating myocardial injury (1). High-sensitivity assays improve analytical detection limits, thereby allowing concentrations to be measured in the majority of healthy individuals. This capability allows an assessment of biologic variation (BV)1 to determine what constitutes a clinically important change in the cardiac troponin concentration, a critical metric for identifying acute events. Such an event is often a myocardial infarction, but any acute cardiac injury can cause increasing and/or decreasing values (1). Accordingly, we evaluated BV for a recently developed high-sensitivity cardiac troponin I (hs-cTnI) assay (2) from Beckman Coulter. We performed this study with the same cohort used to define BV for the high-sensitivity cardiac troponin T (hs-cTnT) assay (3) and according to a protocol approved by our institutional review board. For assessment of short-term BV, we collected blood into serum separator tubes (Becton Dickinson) at 0, 1, 2, 3, and 4 h, centrifuged the tubes, and stored the serum samples immediately at −70 °C. …

Evaluation of direct inoculation of the BD PHOENIX system from positive BACTEC blood cultures for both Gram-positive cocci and Gram-negative rods

BackgroundRapid identification (ID) and antibiotic susceptibility testing (AST) of the causative micro-organism of bloodstream infections result in earlier targeting of antibiotic therapy.In order to obtain results of ID and AST up to 24 hours earlier, we evaluated the accuracy of direct inoculation of the Phoenix system from positive blood cultures (BACTEC) by using Serum Separator Tubes to harvest bacteria from positive blood cultures. Results were compared to those of standard Phoenix procedure. Discrepancies between the two methods were resolved by using the API system, E-test or microbroth dilution.ResultsID with the direct method was correct for 95.2% of all tested Enterobacteriaceae (n = 42) and 71.4% of Pseudomonas aeruginosa strains (n = 7).AST with the direct method showed a categorical agreement for Gram-negative rods (GNR) of 99.0%, with 0.7% minor errors, 0.3% very major errors and no major errors. All antibiotics showed an agreement of >95%.The direct method for AST of Staphylococcus (n = 81) and Enterococcus (n = 3) species showed a categorical agreement of 95.4%, with a minor error rate of 1.1%, a major error rate of 3.1% and a very major error rate of 0.4%. All antibiotics showed an agreement of >90%, except for trimethoprim-sulfamethoxazole and erythromycin.ConclusionsInoculation of Phoenix panels directly from positive blood cultures can be used to report reliable results of AST of GNR a day earlier, as well as ID-results of Enterobacteriaceae. For Staphylococcus and Enterococcus species, results of AST can also be reported a day earlier for all antibiotics, except for erythromycin and trimethoprim-sulfamethoxazole.

Study of a novel method to assist in early reporting of sepsis from the microbiology laboratory

Microbiology laboratories must provide accurate blood culture reports with rapid turnaround time (TAT) to effectively manage patients with sepsis. In this study three methods are compared for reporting blood culture results: a manual method that included use of a serum separator tube (SST), the conventional manual, and an automated method for identification and susceptibility (ID/AST). Broth from positive blood culture bottles was added to an SST and then centrifuged. The pellet obtained was used to directly inoculate biochemical tests for identification and agar plates for AST on the first day of positivity. Biochemicals and AST plates were read the next day and final results reported on the second day at 24 hours. For conventional disk diffusion testing, the newly positive blood culture broth was also inoculated on solid media on the first day and incubated overnight. The next day AST by was performed as well as biochemical tests from pure colonies. These colonies were also used to inoculate panels for ID/AST using the automated MicroScan 40SI System. These results were recorded on the third day and results reported at 48 hours. The study included 851 samples Out of 106 (12.4%) positive blood cultures, 102 were included in the study; Comparison of the 3 methods showed good correlation. Identification was correctly reported in 95 (93.1%) isolates. The overall AST error rate was 3.8%. The use of SST and direct from pellet inoculation reduced TAT for identification and AST results between 18 and 24 hours.

Estimation of the Minimal Preanalytical Uncertainty for 15 Clinical Chemistry Serum Analytes

We sought a model to estimate preanalytical uncertainty of blood samples collected and processed by using optimal procedures. Optimal preanalytical handling of blood samples included use of a loosely fastened tourniquet, wide bore needles, recommended clotting time and centrifugation speed, and minimal storage before analysis. Blood was collected from each arm of 20 volunteers into 2 rapid-serum tubes and 2 serum-separation tubes. Linear mixed-effects models were used to estimate the between-venipuncture SD, the preanalytical SD (excluding venipuncture), the measurement repeatability SD, and systematic differences between the tubes and between venipunctures. No significant systematic differences were found between successive venipunctures. However, statistically significant mean differences were seen between serum-separation tubes and rapid-serum tubes for 7 of the 15 analytes. The preanalytical SD (excluding venipuncture) for lactate dehydrogenase (3.2 U/L, 95% CI 2.8-3.7) was significantly higher than the SD for measurement repeatability (1.9 U/L, 95% CI 1.7-2.1). For potassium both the preanalytical SD (excluding venipuncture) (0.092 mmol/L, 95% CI 0.080-0.11) and the between-venipuncture SD (0.075 mmol/L, 95% CI 0.048-0.12) were significantly higher than the measurement-repeatability SD (0.031 mmol/L, 95% CI 0.028-0.035). For glucose the between-venipuncture SD (0.20 mmol/L, 95% CI 0.14-0.27) was significantly higher than the preanalytical SD (excluding venipuncture) (0.07 mmol/L, 95% CI 0.06-0.08), and the measurement repeatability SD (0.057 mmol/L, 95% CI 0.051-0.064). By applying linear mixed-effects models we have estimated the minimal preanalytical uncertainty that will influence all patient results.

Effect of Anticoagulant and Venipuncture Site on Hematology and Serum Chemistries of the Spiny Softshell Turtle (Apalone spinifera)

The effect of anticoagulant and venipuncture site on hematology and serum chemistries was evaluated in eight captive spiny softshell turtles (Apalone spinifera). Animals were randomly and evenly distributed into two groups. On day 0, blood samples were collected from the dorsal coccygeal vein in turtles from group 1 and from the subcarapacial vein in turtles from group 2. On day 15, the same procedure was repeated, but turtles from group 1 were sampled from the subcarapacial vein and turtles from group 2 from the dorsal coccygeal vein. Hematologic samples were placed in ethylenediaminetetraacetic acid (EDTA) on day 0 and in heparin on day 15. Samples for chemistries were placed in serum separator tubes. All samples in EDTA were hemolyzed. Nonparametric tests were used to assess significant differences in hematologic and biochemical parameters between the two venipuncture sites. Among the biochemical parameters, statistically significant differences were only present for glucose and potassium, with the median values being higher in samples obtained from the subcarapacial vein. Correlation tests did not show any significant correlation between the values obtained from the two venipuncture sites for any of the biochemical parameters evaluated. There was also a general lack of agreement for values obtained from different venipuncture sites. This study concluded that EDTA is not an appropriate anticoagulant for this species, and serum chemistry values from paired samples taken using different venipuncture sites did not have a significant correlation or agreement.

LXR ligand lowers LDL cholesterol in primates, is lipid neutral in hamster, and reduces atherosclerosis in mouse

Liver X receptors (LXRs) are ligand-activated transcription factors that coordinate regulation of gene expression involved in several cellular functions but most notably cholesterol homeostasis encompassing cholesterol transport, catabolism, and absorption. WAY-252623 (LXR-623) is a highly selective and orally bioavailable synthetic modulator of LXR, which demonstrated efficacy for reducing lesion progression in the murine LDLR(-/-) atherosclerosis model with no associated increase in hepatic lipogenesis either in this model or Syrian hamsters. In nonhuman primates with normal lipid levels, WAY-252623 significantly reduced total (50-55%) and LDL-cholesterol (LDLc) (70-77%) in a time- and dose-dependent manner as well as increased expression of the target genes ABCA1/G1 in peripheral blood cells. Statistically significant decreases in LDLc were noted as early as day 7, reached a maximum by day 28, and exceeded reductions observed for simvastatin alone (20 mg/kg). Transient increases in circulating triglycerides and liver enzymes reverted to baseline levels over the course of the study. Complementary microarray analysis of duodenum and liver gene expression revealed differential activation of LXR target genes and suggested no direct activation of hepatic lipogenesis. WAY-252623 displays a unique and favorable pharmacological profile suggesting synthetic LXR ligands with these characteristics may be suitable for evaluation in patients with atherosclerotic dyslipidemia.

Latent Cytomegalovirus Infection Exacerbates Experimental Colitis

Inflammatory bowel disease (IBD) severity is positively correlated with cytomegalovirus (CMV) infection. This may reflect CMV triggering and/or exacerbating flares of IBD and/or IBD or immunosuppressive drugs administered to patients with IBD increasing susceptibility to CMV infection. Herein, we performed studies in mice to investigate these possibilities. Mice administered murine CMV (MCMV) developed signs of acute viral infection (malaise and weight loss) and had MCMV loads that were readily detected in numerous organs including the intestine. By 4 weeks, these mice manifested a "latent" infection in which MCMV levels were low but detectable by PCR. Such MCMV infection did not induce acute colitis in either wild-type mice or IL-10(-/-) mice, which are highly prone to developing colitis. However, underlying MCMV infection in an acute or latent state exacerbated the severity of colitis induced by dextran sodium sulfate (DSS). Such potentiation of DSS colitis by latent MCMV infection seemed to occur without viral reactivation. Whereas initial MCMV infection induced acute alterations in serum and intestinal cytokines, such cytokine levels returned to baseline before administration of DSS. However, the initial infection resulted in lasting elevation of antibodies to commensal bacterial antigens, suggesting that MCMV infection may have potentiated colitis via priming of the intestinal immune response to gut microbiota. Thus, underlying CMV infection can alter mucosal immunity, potentially increasing the tendency of CMV-infected hosts to develop colitis.

Stability of blood analytes after storage in BD SST™ tubes for 12 mo

Objectives We studied the stability of 33 analytes related to clinical chemistry, bone, and vitamin metabolism, after storage in serum separator tubes (SST™). Design and methods Blood was collected from 6 subjects using SST tubes. Some serum remained in the tube in contact with the barrier gel and was stored at − 80 °C for 12 mo. Results Clinically significant changes occurred only in 1,25-dihydroxyvitamin D and retinol-binding protein. Conclusions Freezing SST tubes before sample analysis is a viable option for some analytes.

Assay Imprecision and 99th-Percentile Reference Value of a High-Sensitivity Cardiac Troponin I Assay

We undertook a performance evaluation and determination of the 99th-percentile reference value for the Siemens cTnI-Ultra with a fully characterized population that had undergone noninvasive cardiac imaging. Permission for the study was obtained from the local research ethics committee. Participants >45 years of age were randomly selected from the practice lists of 7 representative local community practices; 1392 individuals from the general population were invited. Demographic data were collected from the participants by questionnaire. Heart rate and blood pressure measurements (mean of 2 readings) and spirometry, electrocardiography, and echocardiography evaluations were performed. For measurements of fasting serum glucose, creatinine, and cardiac troponin, venous blood was collected into Becton Dickinson serum separator tubes and centrifuged. The serum was removed and stored at −70 °C. Frozen samples were thawed to room temperature, mixed, and centrifuged before analysis. The left ventricular ejection fraction was calculated quantitatively with Simpson’s apical biplane method (1). The left ventricular mass was calculated with the Devereux-modified American Society of Echocardiography equation(2). Valvular regurgitation and stenosis were assessed qualitatively on a 5-point scale. Diastolic heart failure …

Homeostatic Role of Transforming Growth Factor-β in the Oral Cavity and Esophagus of Mice and Its Expression by Mast Cells in These Tissues

Transforming growth factor-beta (TGF-beta) is a pleiotropic growth factor; its overexpression has been implicated in many diseases, making it a desirable target for therapeutic neutralization. In initial safety studies, mice were chronically treated (three times per week) with high doses (50 mg/kg) of a murine, pan-neutralizing, anti-TGF-beta antibody. Nine weeks after the initiation of treatment, a subset of mice exhibited weight loss that was concurrent with decreased food intake. Histopathology revealed a unique, nonneoplastic cystic epithelial hyperplasia and tongue inflammation, as well as dental dysplasia and epithelial hyperplasia and inflammation of both the gingiva and esophagus. In an effort to determine the cause of this site-specific pathology, we examined TGF-beta expression in these tissues and saliva under normal conditions. By immunostaining, we found higher expression levels of active TGF-beta1 and TGF-beta3 in normal tongue and esophageal submucosa compared with gut mucosal tissues, as well as detectable TGF-beta1 in normal saliva by Western blot analysis. Interestingly, mast cells within the tongue, esophagus, and skin co-localized predominantly with the TGF-beta1 expressed in these tissues. Our findings demonstrate a novel and restricted pathology in oral and esophageal tissues of mice chronically treated with anti-TGF-beta that is associated with basal TGF-beta expression in saliva and by mast cells within these tissues. These studies illustrate a previously unappreciated biological role of TGF-beta in maintaining homeostasis within both oral and esophageal tissues.

Thyroglobulin measurement on fine‐needle washout fluids: Influence of sample collection methods

Thyroglobulin (Tg) measurement on fine-needle aspiration (FNA) specimens (Tg-FNA) is useful in the management of patients affected by differentiated thyroid carcinoma. However, the preanalytical procedure for FNA-Tg measurement is not standardized. We evaluated the accuracy of FNA-Tg measurement by using different tubes for needle washout fluids collection.Ultrasound-guided FNA was performed on a combined 156 lesions from 108 patients. Following cytology sampling, the needles were rinsed by normal saline and aliquots collected into three different tubes (plain serum tube, serum separator tube, and lithium-heparin tube, respectively). The Tg-FNA was measured by an immunoradiometric assay.The cytological examination was nondiagnostic in six cases, false-positive in one, and false-negative in two cases. The Tg-FNA was higher in plain serum tubes as compared with serum separator and lithium-heparin ones. FNA-Tg measurement on plain serum and serum separator tubes showed a 100% sensitivity while two false-negative results occurred by lithium-heparin tubes (sensitivity 98%).The diagnostic performance of FNA-Tg compared favorably with cytology. However, biases in FNA-Tg measurement may be introduced by different collection tubes. A collection of standardized washout fluids volume into plain serum tubes is highly recommended. Serum separator tubes and lithium-heparin tubes may lower measured FNA-Tg concentration.

Low-Intensity Exercise Exerts Beneficial Effects on Plasma Lipids via PPARγ

An important mechanism by which physical activity reduces the risk of cardiovascular disease is through regulating plasma lipids. We investigated whether low-intensity exercise modulates lipid metabolism and the transcription factors peroxisome proliferator-activated receptor gamma (PPARgamma) and liver X receptor alpha (LXRalpha) responsible for controlling reverse cholesterol transport (RCT). Thirty-four sedentary adults, mean age 45.6 +/- 11.1 yr, participated in an 8-wk low-intensity exercise program consisting of walking 10,000 steps, three times a week. Subjects were randomly allocated to either an exercise group or a sedentary control group, and serum lipid or lipoprotein concentrations were determined. Compared with controls, there was a significant decrease in total cholesterol (preexercise, 5.73 +/- 1.39 mmol x L; postexercise, 5.32 +/- 1.28 mmol x L) and a significant increase in HDL (preexercise, 1.46 +/- 0.47 mmol x L; postexercise, 1.56 +/- 0.50 mmol x L) after the exercise program. There was a significant increase in serum oxidized LDL (oxLDL) concentrations in the exercise group before and after exercise (0 wk, 554 +/- 107 ng x mL; 4 wk, 698 +/- 134 ng x mL; 8 wk, 588 +/- 145 ng x mL). A significant increase in leukocyte mRNA expression for PPARgamma (4 wk, 1.8 +/- 0.9-fold; 8 wk, 4.3 +/- 1.9-fold) was observed, which was reinforced by increased PPARgamma DNA-binding activity postexercise (preexercise, 0.22 +/- 0.09 OD units; postexercise, 1.13 +/- 0.29 OD units). A significant increase in gene expression was observed for the oxLDL scavenger receptor CD36 (4 wk, 3.8 +/- 0.6-fold; 8 wk, 2.7 +/- 0.5-fold) and LXRalpha (8 wk, 3.5 +/- 0.8-fold). Two LXRalpha-regulated genes involved in RCT, namely, ATP-binding cassette transporters A1 and GI (ABCA1 and ABCG1, respectively), were significantly up-regulated postexercise (8 wk: ABCA1, 3.46 +/- 0.56-fold; ABCG1, 3.06 +/- 0.47-fold). We propose that the net effect of these changes may be to increase oxLDL uptake, to stimulate RCT, and thus to promote clearance of proatherogenic lipids from the vasculature, ultimately contributing to the cardiovascular benefits of low-intensity aerobic exercise.

Performance of two tube coagulase methods for rapid identification of Staphylococcus aureus from blood cultures and their impact on antimicrobial management

Test parameters and clinical impact of the direct tube coagulase test (DTCT) for rapid identification of Staphylococcus aureus from blood culture were investigated. The sensitivity of the DTCT at 4 h using saline dilution was 96%, compared with 93% using serum separator tubes; specificity was 100% for both methods. Among 32 patients with S. aureus bacteraemia, treatment modifications were based on microbiology results from the primary source of infection in 12 patients, on a Gram's stain from blood culture in seven patients, and on the DTCT in nine patients. The DTCT is a valuable adjunct in the routine microbiology laboratory because of its good performance, technical simplicity and low cost.

Biological Variation of Myeloperoxidase

Myeloperoxidase (MPO)1 has been shown to play a role in the pathogenesis of coronary artery disease. It is released from activated neutrophils at sites of vascular damage and has been shown to increase in atherosclerotic plaques before the onset of myocardial injury (1). Elevations in MPO occur independently of C-reactive protein (CRP) and other markers of inflammation, and it has been suggested as a marker of risk in patients who have high as well as low cardiac troponin T concentrations and who present with acute coronary syndrome (2). We recruited 12 apparently healthy individuals, 10 women and 2 men with a mean age of 33 years (range 27–43) for estimation of the biological variation of MPO. None had a history of heart disease or any clinically apparent inflammatory processes. Serum samples were collected between 0800 and 1000 on the same day of the week, weekly for 5 weeks as described by Fraser and Harris (3). Venous blood was collected in plastic serum separator tubes. All samples were centrifuged after clotting and were stored …

The Approach and Design of a Surrogate Protease Substrate for Disease Biomarker Discovery

Biomarker discovery investigations utilizing sera samples typically show differences in peptides originating from high abundant proteins. These peptides, produced from the activity of one or more protease(s), by themselves may not reflect a disease-associated biomarker(s), but in fact, show the downstream effect of disease specific protease(s). The ability to select “true” biomarkers of disease is mired by the inter- and intrapatient variability typically observed in a proteomics approach to serum biomarker discovery. As an example, serum from an individual was collected with three types of serum separator tubes (SST) and stored at 4°C for prolonged periods of time. The postcollection integrity of the serum was examined using microcapillary nanoflow reversed-phase liquid chromatography (nano-RPLC) tandem mass spectrometry (MS/MS) of the trypsin-digested, low molecular weight protein fraction. An increase in unique peptides per protein was observed for the highest abundant proteins with prolonged storage times. Of note was the presence of truncated variations of high abundant parent peptides, which presumably arise from the action of endogenous exo- and endo-peptidases in human serum. Based on these observations, a surrogate peptide was synthesized with a central affinity label as a means to screen enzymatic activity in serum. The surrogate peptide was used to screen cell-free media of two human breast cancer cell lines, SKBr3 and MDA-MB-231, for differential enzymatic activity as an initial disease model. In light of these results, the use of a “spiked” protease substrate may provide an additional means to differentiate between sera from diseased versus healthy individuals.

Stability of oleander extract and oleandrin in sera stored in plastic serum separator tubes

Oleander poisoning is common in the southern parts of the United States as well as part of Europe and South East Asia. The fluorescence polarization immunoassay (FPIA) for digoxin cross-reacts with oleandrin, the major poison of oleander extract and can be used for rapid detection of oleander poisoning. However, for medicolegal investigation, the presence of oleandrin should be confirmed by a more sophisticated analytical technique such as liquid chromatography combined with tandem mass spectrometry. We studied stability of oleander extract as well as oleandrin in serum samples stored in Becton Dickinson plastic serum separator tubes (SSTs) by comparing values obtained in parallel specimens stored in plain glass tubes and in red-topped plastic tubes. Oleander leaves were extracted using absolute ethanol, and drug-free serum pools were supplemented with oleander extract or ethanolic solution of pure oleandrin. Aliquots of the supplemented pools were then stored in plain glass tubes, red-topped plastic tubes or SSTs and the stability of oleander extract or oleandrin in sera were studied by the FPIA digoxin assay for varying times up to seven days. We observed no statistically significant change in apparent digoxin concentrations in specimens stored in SSTs even after seven days of storage compared to original values observed in the supplemented serum pools. Specimens can be stored in SSTs for up to seven days prior to analysis of oleandrin concentration.

Influence of Sample Collection and Storage on the Detection of Platelet Factor 4–Heparin Antibodies

Heparin-induced thrombocytopenia is a life threatening thrombotic disorder caused by antibodies to platelet factor 4 (PF4) and heparin. Commercial immunoassays are frequently used for the detection of PF4-heparin antibodies, and several studies have reported that higher antibody titers are more frequently associated with adverse events. It is not known if conditions involving sample preparation and/or storage affect the operational characteristics of PF4-heparin immunoassays. We compared the detection of PF4-heparin antibodies from 48 patient samples collected concordantly in serum separator tubes or tubes containing EDTA or sodium citrate. We also examined the effects of extended sample storage on whole blood collected in serum separator, EDTA, or citrate tubes at 4 degrees C for up to 96 hours on antibody detection. We noted that serum or plasma anticoagulated with sodium citrate or EDTA yielded comparable results. In addition, we could not demonstrate any significant sample deterioration after storage at 4 degrees C in any medium for up to 4 days. These findings suggest that PF4-heparin antibodies are largely insensitive to the effects of sample preparation and storage.

Dengue Virus Detection Using Whole Blood for Reverse Transcriptase PCR and Virus Isolation

Dengue is one of the most important diseases in the tropical and subtropical regions of the world, with an estimated 2.5 billion people being at risk. Detection of dengue virus infections has great importance for the clinical management of patients, surveillance, and clinical trial assessments. Traditionally, blood samples are collected in serum separator tubes, processed for serum, and then taken to the laboratory for analysis. The use of whole blood has the potential advantages of requiring less blood, providing quicker results, and perhaps providing better sensitivity during the acute phase of the disease. We compared the results obtained by reverse transcriptase PCR (RT-PCR) with blood drawn into tubes containing EDTA and those obtained by RT-PCR with blood samples in serum separator tubes from 108 individuals clinically suspected of being infected with dengue virus. We determined that the extraction of RNA from whole blood followed by RT-PCR resulted in a higher detection rate than the use of serum or plasma. Using a selection of these samples, we also found that our ability to detect virus by direct C6/36 cell culture and mosquito inoculation was enhanced by using whole blood but not to the same extent as that seen by the use of RT-PCR.

The effect of potassium EDTA on the stability of parathyroid hormone in whole blood

The stability of parathyroid hormone (PTH) in whole blood has not been well characterized. Previous studies show EDTA plasma samples to be more stable than serum samples. Blood from 17 haemodialysis patients and five healthy volunteers was collected into serum separator tubes (SSTs) and potassium EDTA tubes (EDTA-Ts) and incubated at room temperature before separation and storage for PTH analysis using the Bayer Advia Centaur. Initial PTH concentrations were 7% higher (95% confidence interval [CI] 2-16%, P=0.016) in EDTA-Ts compared to the SSTs in the renal cohort. PTH concentrations in SSTs were significantly lower after 8 (10%, 95% CI 3-17%) and 20 h (22%, 95% CI 11-31%) but did not change significantly in EDTA-Ts (P=0.1543). PTH concentration in EDTA-Ts from healthy volunteers was also independent of incubation time (P=0.1165). The greater stability of PTH in whole blood anticoagulated with potassium EDTA allows PTH analysis to be offered to sites such as satellite clinics and primary care sites which do not have centrifugation and refrigeration facilities.