Post-analytical ’error’ rates in point-of-care testing: use of a quality assurance programme

Received: 19 October 2000Accepted: 30 April 2001

Presented at “Antwerp 2000: Quality in the Spotlight in Medical Laboratories” Conference, 19–20 October 2000, Antwerp, Belgium

Abstract Laboratory tests are sub-ject to error, pre-analytical, analyti-cal and post-analytical. Post-analyti-cal error includes misinterpretationof results. Point-of-care testing(POCT) can be subject to the sameerrors This study utilized an externalquality assurance programme forcapillary blood glucose and ‘dip-stick’ urinalysis to investigate post-analytical errors of result interpreta-tion by various grades of nurse per-forming POCT. When the resultssimulated a hypoglycaemic patient,84.1% of nurses interpreted the re-sults correctly. In the case of diabe-tes mellitus, 95.7% of nurses inter-

preted the results correctly. Whereasin the simulation of a case where thecapillary blood glucose was falselyraised due to puncture site contami-nation only 5.4% of nurses interpret-ed the POCT results correctly. As theseniority of the nurse made little orno difference to the interpretationgiven, this study demonstrated theneed for improved training withinthe Taunton and Somerset NHSTrust Hospital.

Keywords Quality assurance ·Point-of-care systems · Bloodglucose · Urinalysis · Nursing education

Accred Qual Assur (2001) 6:402–404© Springer-Verlag 2001 GENERAL PAPER

Paul Tighe Post-analytical ‘error’ ratesin point-of-care testing: use of a qualityassurance programme

Introduction

Errors in laboratory testing have been divided into thoseoccurring prior to analysis (pre-analytical), during analy-sis (analytical) and after analysis (post-analytical). Causesof post-analytical error include misinterpretation of theresults Point-of-care testing (POCT) results may similarlybe subject to misinterpretation. In the United Kingdomsome POCT, commonly capillary blood glucose and uri-nalysis, is undertaken by nurses, following training, aspart of the routine nursing duties. Analytical errors in‘dipstick’ urinalysis have been demonstrated [1]. Thisstudy was designed to evaluate the post-analytical errorrate in POCT using a quality assurance (QA) programmeset up to monitor ward-based testing at this hospital [2].The programme consisted of an aqueous blood glucosesample and an aqueous urine sample to be analysed byall nurses within the Taunton and Somerset NHS TrustHospital, these samples were matched to simulate threepossible case scenarios.

Methods

Approximately 250 of the 2000 nurses in the hospitalcomplete POCT QA testing each month. Capillary bloodglucose was measured using the Medisense precisionQID meter and Precision Plus sensors (Abbott, Maiden-head UK ) and urinalysis using Multistix 8SG (Bayer,Newbury, UK).

As part of the programme each nurse was asked to an-swer the following two questions based on the resultsachieved. All nurses were advised to assume that thesewere the results from a typical patient in their particularward or clinic:

1. Are there any abnormalities?2. What further action or tests would you undertake on

the basis of these results?

The grades of nurse included in the QA programme aredefined in Table 1. Details of the three cases used in thisstudy are given in Table 2, together with suggested ‘cor-

P. TigheDirectorate of Laboratory Medicine,Taunton and Somerset NHS Trust,Musgrove Park, Taunton TA1 5DA, UKe-mail: [email protected].: +44-1823-342278

403

rect interpretation’ for each case. The responses werescored depending on the nursing grade.

Results Results were analysed on the basis of the grade of nurse,Nursing Sister, Staff Nurse and Health Care Assistantand for the purposes of this study on the basis of the ‘re-sults achieved’ rather than the ‘correct result’, as thisstudy was looking at result interpretation rather than an-alytical competence. Health Care Assistants wereawarded a correct score for giving either answer A or B,whereas Nursing Sisters or Staff Nurses were onlyawarded a correct score for answer B.

The results of the study are given in Tables 3–5. Allresults are given as the number of staff giving the partic-ular answer, with percentages for that staff group in pa-renthesis. Case A: Results (Table 3) from samples simulating a pa-

tient with a low capillary blood glucose and a ‘nor-mal’ urine. Of the 24 responses with ‘incorrect inter-pretation’, 9 recorded ‘no abnormality detected’. Theother 15, whilst making no comment on the low glu-cose, would have sent the urine for culture because ofa trace result they detected for urine protein.

Case B: Results (Table 4) from samples simulating a pa-tient with a raised capillary blood glucose and urinecontaining both glucose and ketones. All respondents

giving ‘incorrect interpretation’ answers suggestedurine culture.

Case C: Results (Table 5) from samples simulatingeither, a patient in renal failure where an unwashedcapillary blood puncture site contaminated the blood

Table 1 Nursing grades in United Kingdom hospitals

Type of nurse Definition

Nursing Sister Senior Nurse/Ward ManagerStaff Nurse Qualified NurseHealth Care Assistant Unqualified Nursing Assistant

Table 2 Analytical results forcases A, B and C, together withthe expected “correct” answers

Analyte Case A Case B Case C

Blood Glucose 2.6 mmol/l 16.9 mmol/l 28.0 mmol/lUrine Glucose Negative 20 mmol/l NegativeUrine Ketones Negative 1.0 mmol/l NegativeUrine Spec. Gravity 1.017 1.007 1.027Urine Blood Negative Negative Positive+++

Urine PH 7.25 5.75 7.25Urine Protein Negative Negative 10.0 g/lUrine Nitrite Negative Negative NegativeUrine Leucocyte Negative Negative Negative

Suggested ‘correct’ A. Show results to a A. Show results to a A. Show results to a interpretation senior colleague senior colleague. senior colleague.

B. Any comment B. Any comment B. Any comment indicating low recognizing undiagnosed recognizing theblood glucose. or out of control inconsistency of the

diabetes mellitus results, recommending repeat of one or bothtests immediately

Table 3 Results for case A given as numbers of participants ateach nursing grade and as a percentage

Grade of nurse ‘Correct ‘Incorrectinterpretation’ interpretation’

Nursing Sister 22 (73.3%) 8 (26.7%)Staff Nurse 55 (87.3%) 8 (12.7%)Health Care Assistant 50 (86.2%) 8 (13.8%)Total (all nurses) 127 (84.1%) 24 (15.9%)

Table 4 Results for case B given as numbers of participants ateach nursing grade and as a percentage

Grade of nurse ‘Correct ‘Incorrectinterpretation’ interpretation’


Table 5 Results for case C given as numbers of participants ateach nursing grade and as a percentage

Grade of nurse ‘Correct ‘Incorrect interpretation’ interpretation’


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glucose test or a mix-up of patient’s urine samples.The ‘incorrect interpretation’ group contained 8 Nurs-ing Sisters, 26 Staff Nurses and 7 Health Care Assis-tants who suggested that they would repeat the testsafter varying periods of time (1, 2 or 4 h), the othersintimated that they would record the results as usualin the patient’s file.

Discussion

POCT tests for blood glucose and urinalysis are generallyregarded as technically undemanding procedures whichcan, with training, be undertaken by nurses outside of thelaboratory environment The study demonstrated the im-portance of post-analytical errors when these tests were

performed by nursing staff. The similarity of responsebetween the three staff grades may suggest that the train-ing of all staff performing these types of test must in-clude ‘what it means’ as well as ‘how to do it’.

Conclusions

The results of this study demonstrate a training need inour hospital and raise issues of the post-analytical errorrates of other POCT tests in use throughout the healthcare system.

Acknowledgements Thanks to Brian Jones (Lab. Medicine) andJudy Moss (Med. Photography) at Taunton and Somerset NHSTrust for their help in preparing this paper.

References

1. Tighe P (2000) Accred Qual Assur5:488–490

2. Tighe P (1999) Br J Biomed 56:6–15

Documents

Post-analytical ’error’ rates in point-of-care testing: use of a quality assurance programme