Preventing Pre-analytical Errors

Vol. 22 • Issue 5 • Page 24


Laboratory data influence 70% of medical diagnoses. This fact indicates that the laboratory is a major aid to the clinicians who have requested the tests. Furthermore, it means that the laboratory must try to reach the goal of zero defects.

The testing process has been divided into three major parts (pre-, intra- and post-analytical), each with a few aspects that can be identified and, in many cases, quantified. Thus, the testing process lends itself to designing a systematic approach to error detection and correction, hopefully before data are reported. While some schemes include “choosing the test” as part of the pre-analytical phase, this article will not include it.

Pre-analytical Breakdown

The pre-analytical phase includes:

• the requisition/order,

• the patient identification before drawing a sample,

• the proper sample (e.g., a ‘red top tube’),

• sufficient amount of sample

• the sample drawn in the proper order,

• avoiding hemolysis whilst drawing the sample,

• the time it takes to deliver the sample to the lab and

• the time required to enter the sample into the intra-analytical phase.

The pre-analytical phase is the most vulnerable part of the total testing process and is considered to be among the greatest challenges to laboratory professionals. Although a number of standards relating to blood sampling, sample transportation and ðhandling are available, conformity is low.1

According to reliable data,2 pre-analytical errors still account for nearly 50% – 70% of all problems occurring in laboratory diagnostics. Although most of these errors are “intercepted” before inappropriate reactions are taken, in nearly 20% of cases they produce inappropriate investigations, including more unnecessary testing and, thus, unjustifiable increase in costs, while generating inappropriate clinical decisions and causing some unfortunate circumstances.3 For example, “Out of all laboratory problems, up to 61% are associated with the preanalytical phase in the lab. Out of this, 33% of the errors are associated with the test request forms, 18% errors with sample collection.”4

Studies on Patient Safety

Electronic systems to prevent medical personnel from drawing blood from the wrong patient, and in the proper order, were introduced commercially in the early 1990s. Correct patient identification and test tube labeling before phlebotomy are of extreme importance for patient safety. Olayemi and Asiamah-Broni pointed out that the implementation of advanced information technology and robotics in the pre-analytical phase have improved accuracy and clinical efficiency of the laboratory process, and created a process “that minimizes errors.”5

Four different ways of taking blood were tested to see the effect on hemolysis: cannulation and a syringe (38%); cannula with evacuated tube and adaptor (42%); syringe and needle into vein (14%); and evacuated tube system used conventionally (6%).6 Where a syringe was used, two methods of transfer into the sample tube were observed – needle kept on with cap piercing (77%) and needle and evacuated cap both removed (23%). On 20 out of 50 phlebotomy episodes (40%), the potassium-EDTA tube was filled prior to the biochemistry serum gel tube. A search of the laboratory computer records for ward-based phlebotomy found 30 of 1,034 samples were hemolysed (2.9%). In the 50 phlebotomy episodes in the “major” area of the emergency department, 24% produced a hemolysed sample (P < 0.0001). For samples taken from all areas of emergency medicine over a seven-day period, 52 of 485 were hemolysed (10.7%; P < 0.0001).

This study has shown that phlebotomy techniques in the ED deviate from standard practice significantly. This may well be a reason for the much higher frequency of hemolysed samples and with the wrong order of collection the possibility of potassium-EDTA-contaminated samples.7

Effects of Hemolysis

Lippi and his co-workers8 studied the effects of hemolysis (a major factor on pre-analytical errors), as well as elevated bilirubin and elevated triglycerides. Inaccuracy attributable to hyperbilirubinemia is less significant using modern instruments equipped with dedicated wavelengths (i.e., with readings at 650 nm or above), so that test results in samples with a bilirubin concentration up to 20 mg/dL can still be analytically reliable. The interference observed in lipemic samples is most evident with readings using wavelengths lower than 500 nm and can be prevented with readings at 650 nm or above, and/or using higher dilutions of the test sample, or can be abated in high hypertriglyceridemic specimens (i.e., > 1,000 mg/dL) using high speed micro-centrifugation, lipid extraction with organic solvents such as fluorine-chlorinated hydrocarbon, or lipid-clearing agents such as LipoClear (StatSpin Inc., Norwood, MA) and n-hexane.9

Harrison et al.10 found that laboratory processing times were not responsible for the hemolyzed specimens, nor was the collection equipment. The ED had an excessive number of hemolyzed specimens when compared to the rest of the medical center. The collection techniques in the ED appeared to be the origin of the problem.

Additionally, they studied samples from the EMS (n = 200) and the ED (n = 200). The redraw rate was higher for the ED group (11.5%) than the EMS group (9.5%).10 The primary reason for redraw in the EMS group was insufficient quantity (52.6%; ED=8.7%). The primary reason for redraw in the ED group was hemolysis (52.2%; EMS=31.6%). Median ED throughput time was 17 minutes less for the EMS group (163 minutes) than for ED group (180 minutes). No incidences of undue blood exposure was seen in either group.

Specimen Transport

Sample transportation is one of the major factors contributing to delays in returning high-quality clinical laboratory results to the patient bedside. Furthermore, sample quality can be compromised by exposure to extremes of temperature and physical forces during transportation. Uncontrolled temperature-induced errors are well understood and often prevented by using environmentally controlled transportation containers.11 The educational program for nursing personnel is relevant, as evidenced by a decrease of sample errors and resulting quality improvement.12

A variety of resources are available to aid in managing the extra-analytical phase. The recent publication of quality indicators and proposed performance levels by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) working group on laboratory errors and patient safety provides particularly useful benchmarking data.13

For many years, the clinical laboratory’s focus on analytical quality has resulted in an error rate of 4 – 5 sigma, which surpasses most other areas in healthcare. As more laboratories use electronic readers for orders and patient identification, one of the major sources of error will decrease. Implementing procedures to avoid hemolysis and a reduction in time from the draw to the intra-analytical phase will move the laboratory closer to the goal of zero defects.

David Plaut is a chemist and statistician in Plano, TX.


1. Preanalytical phase–a continuous challenge for laboratory professionals. Biochem Med (Zagreb). 2012;22(2):145-9, Simundic AM, Lippi G.

2. Preanalytical quality improvement: from dream to reality.Clin Chem Lab Med. 2011 Jul;49(7):1113-26. Lippi G, Chance JJ, Church S, et al. see also Ann Clin Biochem. 2008 Sep;45(Pt 5):463-6. and Clin Lab. 2011;57(9-10):749-52.Preanalytical error occurrence rate in clinical chemistry laboratory of a public hospital in India. Singla P, Parkash AA, Bhattacharjee J

3. Incomplete laboratory request forms: the extent and impact on critical results at a tertiary hospital in South Africa., Ann Clin Biochem. 2008 Sep;45(Pt 5):463-6, Nutt L, Zemlin AE, Erasmus RT.

4. Inappropriate investigations Incomplete laboratory request forms: the extent and impact on critical results at a tertiary hospital in South Africa. Pan Afr Med J. 2011;8:33, Nutt L, Zemlin AE, Erasmus RT.

5. Evaluation of request forms submitted to the haematology laboratory in a Ghanaian tertiary hospital, Ann Clin Biochem. 2011 Nov;48(Pt 6):562-5, Olayemi E, Asiamah-Broni R.

6. Variation in phlebotomy techniques in emergency medicine and the incidence of haemolysed samples, Ann Clin Biochem. 2011 Nov;48(Pt 6):562-5, Berg JE, Ahee P, Berg JD.

7. Preanalytical error occurrence rate in clinical chemistry laboratory of a public hospital in India, Clin Lab. 2011;57(9-10):749-52, Singla P, Parkash AA, Bhattacharjee J.

8. Interference in coagulation testing: focus on spurious hemolysis, icterus, and lipemia Semin Thromb Hemost., 2013 Apr;39(3):258-66, Lippi G, Plebani M,

9. A comparison of the quality of blood specimens drawn in the field by EMS versus specimens obtained in the emergency department, J Emerg Nurs. 2010 Jan;36(1):16-20, Favaloro EJ.

10. Reducing preanalytical laboratory sample errors through educational and technological interventions, Harrison G, Speroni KG, Dugan L, et al.

11. Preanalytical Errors Introduced by Sample-Transportation Systems: A Means to Assess Them, Clin Chem. 2011 Oct;57(10):1349-50, Felder RA.

13. Reducing preanalytical laboratory sample errors through educational and technological interventions. Clin Lab. 2012;58(9-10):911-7, Lillo R, Salinas M, Lopez-Garrigos M et al.

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