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Letters |
Division of Clinical Laboratories, Bikur Cholim Hospital, 5 Strauss Street, Jerusalem 91004, Israel
a Author for correspondence. Fax 972-2-6464289; e-mail
almagors{at}hotmail.com.
To the Editor:
Numerous preanalytical variables may affect the outcome of clinical laboratory tests (1)(2)(3). Blood-collection procedures are considered an important impact factor because they are associated with several possible sampling problems, including the use of a tourniquet with hand-clenching, the site of venipuncture, hemolysis because of venipuncture, and the inappropriate use of sample tubes.
In our hospital, two systems are used for venous blood collection: the Becton Dickinson (BD) VacutainerTM system and the Greiner Vacuette® system (Greiner Labortechnik GmbH). The BD product includes a specific blood-collection needle, a holder into which the needle is assembled before phlebotomy, and evacuated blood collection tubes. The Greiner product consists of a sterile holder (Holdex®) with a luer adapter to fit regular needles and evacuated blood collection tubes. The design of the BD needle holder enables direct linear flow of blood from the venipuncture site into the blood collection tubes. The Greiner Holdex was designed with an offset luer adapter to enable a convenient puncture angle. Therefore, the straight path within the Holdex is interrupted twice by angles of 90°, thus forming three consecutive flow segments. These changes in the linear flow of blood might impose mechanical strain on blood cells, affecting membrane integrity, which may cause efflux of intracellular constituents into the serum.
We compared the Greiner system to the BD system by evaluating within-subject variations in the results of blood analyses.
Fifty-five healthy individuals participated in our study (mean age ± SD, 26.7 ± 4.3 years). Seventeen volunteers were women (age, 25.8 ± 2.1 years) and 38 were men (age, 27.2 ± 5.0 years). All resided in Jerusalem and its environs. The study protocol was approved by the institutional research ethics board, and all subjects gave their informed consent.
The study participants were seated for 5 min before the tourniquet was applied. Hand-clenching was avoided. A 21-gauge needle attached to its specific holder (BD or Greiner) was inserted into the antecubital vein, and blood was collected into evacuated tubes (into the serum separation tube, followed by the citrate tube, and then into the EDTA tube). The tourniquet was released when blood began flowing into the first tube. The tubes were inverted six times after withdrawal from the holder to ensure proper mixing of the blood with anticoagulants. Phlebotomy was performed twice in each patient. By random assignment, the BD blood-collection system was used in one arm and the Greiner blood collection system was used in the opposite arm.
Serum and plasma were prepared by centrifugation of blood (1200g for 10 min) at room temperature within 30 min of collection. Each serum sample was analyzed for sodium and potassium using ion-selective electrodes (Cobas Integra chemistry analyzer; Hoffmann-La Roche). Additionally, aspartate aminotransferase, alanine aminotransferase, amylase, alkaline phosphatase, lactate dehydrogenase, bilirubin, HDL-cholesterol, magnesium (Mg2+), and calcium were determined by specific colorimetric assays (Cobas Integra analyzer). Differential blood counts were carried out using the Vega blood cell counter (ABX Hematologie). Coagulation assays [prothrombin time (PT), activated partial thromboplastin time, and fibrinogen] were performed with the ACL 1000 coagulation analyzer (Instrumentation Laboratory). Hemoglobin in plasma was measured by spectrophotometric scanning technique as described previously (4).
Statistical analyses were performed with the use of SPSS statistical software (Ver. 7.5.21). Differences in quantitative variables were assessed for statistical significance with the Student paired t-test.
In blood samples obtained by the nonlinear blood collection system
(Greiner), significant increases were observed in serum
Mg2+ concentration, plasma hemoglobin, and PT
(Table 1
). All other analytes were essentially unchanged compared with
the direct-flow system (BD). The 31% increase in hemoglobin was not
accompanied by changes in serum potassium concentrations and lactate
dehydrogenase activity. This indicates that the extent of
erythrocytolysis was relatively low and the leakage of intracellular
constituents was negligible. Our results are consistent with the study
by Sonntag (2), which showed that the concentrations of
potassium and lactate dehydrogenase in serum are affected by hemoglobin
concentrations 
0.2 g/L.
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Unexpectedly, we measured a 2.4% increase in Mg2+ concentrations in the Greiner samples. We assumed that optical interference of hemoglobin caused the artifactual increase in Mg2+ in these samples. Hypomagnesemia is associated with alcoholism, pancreatitis, gastrointestinal diseases, glomerulonephritis, hyperthyroidism, hyperparathyroidism, metabolic acidosis, and drug administration. Furthermore, in patients with acute myocardial infarctions, serum Mg2+ <0.82 mmol/L may increase the risk of ventricular arrhythmia. Falsely increased concentrations of Mg2+ might then be a concern if the Greiner system is used. Presumably, in such cases the Mg2+ assay with an ion-selective electrode is preferable to the spectrophotometric method.
The 8% increase in PT values after blood collection with the Greiner
system (Table 1
) may be a result of interference with clot formation.
We assume that membrane phospholipids exposed by the slight
erythrocytolysis may compete with the PT reagent (thromboplastin) used
for the assay of extrinsic pathway factors, causing prolongation of PT.
It is also possible that the different composition of the coagulation
tubes (glass in the BD vs plastic in the Greiner) may have affected the
results.
Although the degree of hemolysis was significantly higher in the Greiner system than in the BD system, all test results remained within the reference intervals for the young healthy individuals in our study. However, in hospitalized patients, quantitative differences in blood analytes may be accentuated, particularly when intravascular erythrocyte destruction is expected to occur, such as in bacterial or viral infections (5), hypersplenism, cardiac and hepatic abnormalities (6), exposure to venoms and toxins (6), and the use of oxidant drugs (7).
Obviously, the decision of which blood-collection system (or systems) should be used in a healthcare center depends on considerations of cost, safety, and convenience. Along with these considerations, it is appropriate to document the effect of a specific system on laboratory test results.
References
The following articles in journals at HighWire Press have cited this article:
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  G. Lippi and G. C. Guidi Effect of Specimen Collection on Routine Coagulation Assays and D-Dimer Measurement Clin. Chem., November 1, 2004; 50(11): 2150 - 2152. [Full Text] [PDF]
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