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Letters |
a Address correspondence to this author at: Servizio di Medicina di Laboratorio, Azienda Ospedaliera di Padova, Via Giustiniani 2, 35128 Padova, Italy. Fax 39-49-66-32-40; e-mail pad08821{at}pd.nettuno.it
Department of Laboratory Medicine, University-Hospital, 35128 Padova, Italy
To the Editor:
Clinical laboratories must improve the preanalytical phase, a phase highly susceptible to mistakes (1). In some reports, hemolyzed specimens, the most common reason for rejection, account for ~60% of rejected specimens, fivefold more than the second most common cause (2). Cellular contents can falsely increase values for some plasma constituents, such as potassium, lactate dehydrogenase, and aspartate aminotransferase (3). Moreover, hemolysis produces spectrophotometric interference with other laboratory methods.
In vitro hemolysis depends mainly on the way in which the blood samples are drawn and treated, and it may in particular depend on the blood being forced through too fine a needle (4) or through the large-bore needle of a syringe into a tube; it may also be caused by shaking the tube too vigorously and/or centrifuging blood specimens before clotting is complete. In vivo hemolysis, on the other hand, may have at least 50 causes. We evaluated the causes of hemolysis in samples received by our STAT section in the Department of Laboratory Medicine of the University Hospital of Padova, which performs all clinical chemistry tests on specimens collected using lithium heparin as anticoagulant (Becton Dickinson).
Specimens, collected by physicians or nurses from hospitalized patients, were mainly from the departments of internal medicine (28%) and surgery (21%), intensive care units (23%), the emergency department (16%), and the department of organ transplantation (9%). Over a 30-day observation period, we evaluated 27 540 blood specimens from 15 323 sample requests for clinical chemistry, coagulation, and toxicological tests. According to the study protocol, each time hemolysis was visually identified, even if it was only slight, the laboratory contacted the phlebotomists to find out the procedure utilized for vascular access, the technique used for drawing blood, and to obtain information on the transportation, preservation, and storage of the specimens. If no errors in these procedures were identified and in vivo hemolysis was not suspected clinically, serum haptoglobin was measured immediately and at 24 h with a view to confirming the presence of any acute hemolysis, which was clinically evaluated and then confirmed in a further phase.
We identified 505 hemolyzed specimens (3.3%); of these, 64% were affected by a small degree (<50 mg/L of hemoglobin) of hemolysis, 31% by an intermediate degree, and 5% by a high degree (>300 mg/L of hemoglobin). The concentration of hemoglobin in plasma was measured by a colorimetric assay (Plasma hemoglobin; Sigma-Aldrich). The percentages of hemolyzed specimens were similar in the internal medicine and surgery departments (3.1%), intensive care units (3.5%), the emergency department (3.3%), and in the department of organ transplantation (3.4%).
In most cases it was possible to relate the presence of hemolysis to a
specific cause because of the cooperation of phlebotomists and nurses,
and only 26 (5.1%) cases remained unresolved (Table 1
). Importantly, hemolysis from excessive aspiration force was relatively
frequent, mainly in the case of small or superficial veins. Another
frequent cause was the presence of a partial obstruction of an arterial
catheter, leading to an increase in the aspiration force when a syringe
was used to collect the sample. Yet another cause was hemolysis caused
by forcing blood from a syringe into a tube, which was confirmed by
observing a difference in the degree of hemolysis in the different
tubes filled with blood from the same syringe. Collection of samples by
syringe was associated with a higher rate of hemolysis as 83.8% of
hemolyzed specimens were collected with syringes, vs 70% of the total
number of specimens. In vivo hemolysis accounted for 16 of 505 cases
(3.2%); 7 of these cases were associated with prolonged extracorporeal
circulation during cardiac surgery; 2 with of acute ethanol toxicosis,
3 with transfusional reactions, 1 with necrotic-hemorrhagic
pancreatitis, 1 with rhabdomyolysis from drug overdose, and 2 were of
unknown etiology. Importantly, in 5 of the 16 cases, the presence of
hemolysis was not suspected by clinicians, and the laboratory finding
was essential in identifying the presence of a critical situation, thus
potentially improving the medical outcome.
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We conclude that:
References
The following articles in journals at HighWire Press have cited this article:
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  M. A. Halm and M. Gleaves Obtaining Blood Samples From Peripheral Intravenous Catheters: Best Practice? Am. J. Crit. Care., September 1, 2009; 18(5): 474 - 478. [Full Text] [PDF]
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 V. Brescia, M. Tampoia, and A. Mileti Evaluation of Factitious Hyperkalemia in Hemolytic Samples: Impact of the Mean Corpuscular Hemoglobin Concentration Lab Med, April 1, 2009; 40(4): 224 - 226. [Abstract] [Full Text] [PDF]
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 P. Bonini, M. Plebani, F. Ceriotti, and F. Rubboli Errors in Laboratory Medicine Clin. Chem., May 1, 2002; 48(5): 691 - 698. [Abstract] [Full Text] [PDF]
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