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Correspondence - diagnostic blunders

from Teresa K Teal, Northwick Park Hospital, Harrow
and Ruth Lapworth, William Harvey Hospital, Ashford

Dear Bandolier ,

We are pleased that Bandolier has now highlighted the important subject of blunders that affect diagnostic testing [1].

Unfortunately, the analytical blunder rate quoted for external quality assurance [EQA] samples in our study [2] was incorrect. The figure of 0.35% per analyte was the overall blunder rate, whereas the analytical blunder rate was less than 0.1%; more than one third of the errors were transcription mistakes and a further third were due to preanalytical errors.

The consistency in blunder rates quoted in your article is remarkable considering the different methods used to collect and detect blunders in the various studies [2,3,4,5]. Similar rates have also been reported by biochemists in two studies using QA samples [6,7] and in another survey using patient samples in a stat laboratory [8].

From these disparate studies an analytical blunder rate of about 0.05% emerges with overall blunder rates of 0.35% and about 1.0% for patient and QA samples respectively. Higher detection rates will occur in periods of intense scrutiny compared to routine vigilance. The precise way in which blunders are classified will also affect their occurrence. Both these factors may have contributed to the higher and unacceptable blunder rates detected in some laboratories in the Australian study [5].

Extension of the traditional method of assessing QA data in Clinical Biochemistry laboratories is a realistic way of monitoring blunder rates. However, many of the errors affecting EQA samples are due to pre- and post-analytical steps which do not occur in the processing of patient samples in fully automated and computerised laboratories.

We believe that all clinical laboratory disciplines should monitor and review blunders that affect patient samples as well as those reported by EQA schemes as part of their routine QA procedure. This will enable resources to be targeted to problem areas. It is also essential that users of the service are aware that blunders can, and will always occur, even in well managed laboratories.


  1. Blunders. Bandolier 1998 5: 6-7.
  2. Lapworth R, Teal TK. Laboratory blunders revisited. Annals of Clinical Biochemistry 1994 23: 78-84.
  3. Witte DL, Van Ness SA, Angstadt DS, Pennell BJ. Errors, mistakes, blunders, outliers, or unacceptable results: how many? Clinical Chemistry 1997 43: 1352-6.
  4. Chambers AM, Elder J, O'Reilly D St J. The blunder rate in a clinical biochemistry service. Annals of Clinical Biochemistry 1986 23: 470-3.
  5. Khoury M, Burnett L, Mackay MA. Error rates in Australian chemical pathology laboratories.. Medical Journal of Australia 1996 165: 128-130.
  6. Thijssen JHH. Immunoassays in Endocrinology. Communication in Laboratory Medicine 1992 3: 146-151.
  7. Diver MJ. Flunders or blyers - how often do they occur:? Proceedings of EQAS meeting 1990 16-19.
  8. Plebani M, Carraro P. Mistakes in a Stat laboratory: type and frequency. Clinical Chemistry 1997 43: 1348-51.

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