Results from the ICD-10 v2010 bridge coding study: stillbirths and neonatal deaths

Transcription

1 Statistical Bulletin Results from the ICD-10 v2010 bridge coding study: stillbirths and neonatal deaths Date: 1 February 2011 Coverage: England and Wales Theme: Health The software used by Office for National Statistics (ONS) for cause of death coding has been updated this year from the International Classification of Diseases, Tenth Revision (ICD 10) v to v2010. This bulletin presents the main findings from a bridge coding study of 2009 stillbirth and neonatal death registrations (in which deaths were independently coded using v and v2010), to help users understand the impact of this change on perinatal mortality statistics for England and Wales. The impact of ICD 10 v2010 on other deaths has been investigated in a separate study. The main changes in ICD 10 v2010 are amendments to the rules used to assign underlying cause of death. However, stillbirths and neonatal deaths are certified using a perinatal death certificate where underlying cause is not assigned in the usual way. Therefore these main changes do not affect stillbirths and neonatal deaths. There were no new codes or changes to cause of death codes in the Pregnancy, Childbirth and Postnatal Care chapter. The introduction of a new code (P91.6) to further specify hypoxia does not alter the broader group of deaths due to asphyxia at, before or during labour. This was the main amendment for Certain Conditions Originating in the Perinatal Period. One minor change concerned a rare disorder for the Congenital Malformations, Deformations and Chromosomal Abnormalities chapter. Eisenmenger s defect remains as Q21.8 but Eisenmenger s syndrome or complex move to the Diseases of the circulatory system chapter. At ONS, unexplained deaths in infancy were defined by combining Sudden Infant Death Syndrome (R95) with unascertained deaths (R99). In ICD 10 v2010, R99 still includes unspecified causes of mortality such as undetermined natural causes but a new code R97 groups deaths where the cause remained unknown. Office for National Statistics Statistical Bulletin 1

2 Introduction In January 2011, the Office for National Statistics (ONS) introduced a new version of the 10th revision of the International Classification of Diseases (ICD 10) used to code cause of death. ICD 10 was introduced in England and Wales in January Since then amendments have been authorised by the World Health Organisation (WHO) to correct errors in the software supporting the automatic coding or to accommodate new codes in response to new conditions, such as the H1N1 virus (swine flu). Some of these corrections have been implemented by ONS manually. Throughout this period the international community using ICD 10 has determined changes to the classification to reflect new understandings about how causes of death are attributed. Most of the decisions impact on the rules which determine a single underlying cause from the list of conditions mentioned on the death certificate. This underlying cause is either the disease which initiated the train of events leading directly to death or the circumstances of the accident or violence which produced the fatal injury. These rules are applied to all death certificates in England and Wales for deaths occurring from 28 days after birth and older. Stillbirths and neonatal deaths A stillbirth is where a baby is born after 24 or more weeks completed gestation and does not, at any time, breathe or shows signs of life. The 24 weeks relate to the gestation period before the fetus is delivered irrespective of the gestational age when it is thought to have died. Any death before 24 weeks gestation (a fetal death) is not certificated and ONS does not report on these deaths. Neonatal deaths are those which occur under 28 days following a live birth. If the baby showed any sign of life, this is considered a live born child irrespective of the number of weeks duration of a pregnancy. In 1986 England and Wales introduced a special certificate for stillbirths and neonatal deaths following the recommendations of WHO at the international conference for the 9th Revision of the International Classification of Diseases 1. These certificates are designed to collect information about the mother and the fetus or baby in order to determine the earliest cause in the chain of events that led to the death of the fetus or baby. While this certificate permits more flexibility for those completing the certificates it is not possible to derive an underlying cause directly from the information recorded. This means that the main amendments implemented in ICD 10 v2010 do not impact on the cause coding of stillbirths and neonatal deaths. There are two ways of considering cause codes for stillbirths and neonatal deaths. All codes relating to the cause of death text ( mentions ) can be examined. The certificates have two rows relating to conditions in the fetus or baby, two pertaining to conditions in the mother and a fifth row for general conditions which may relate to both or either. Each row may have several codes allocated to it. A second approach to enable a better understanding of the causes relating to stillbirths and neonatal deaths is to group the mentions. ONS devised a hierarchical classification system 2 to identify a single underlying mechanism based on the Wigglesworth classification 3. The cause Office for National Statistics Statistical Bulletin 2

3 groups are organised around the likely timing of the condition or damage leading to the death in relation to birth: before, during or, for neonates, after. New and amended codes present in ICD 10 v2010 will be added to the algorithm creating the ONS cause groups for stillbirths and neonatal deaths. The ICD 10 manual groups diseases into chapters. The three chapters which are most relevant for stillbirths and neonatal deaths are Chapter XV Pregnancy, Childbirth and the Puerperium (codes O00 O99); XVI Certain Conditions Originating in the Perinatal Period (Codes P00 P96); and XVII Congenital Malformations, Deformations and Chromosomal Abnormalities (Codes Q00 Q99). Each chapter is further divided into blocks, for example the birth trauma grouping is one of 10 blocks in Chapter XVI. Bridge coding study To understand and quantify the impact of the introduction of ICD 10 v2010 on mortality statistics, ONS carried out a bridge coding study in which deaths were independently coded using the ICD 10 introduced in 2001 (ICD 10 v2001.2) and the new ICD 10 version 2010 (ICD 10 v2010). Stillbirths and neonatal deaths are not processed through the main Automated Cause Coding System (PC-ACCS) to determine underlying cause but are instead run through a modified version of the ONS software. This TRACER dictionary system allocates ICD 10 codes to all mentions. The v coding was performed on TRACER in the main production environment and records were then extracted and run through the updated TRACER dictionary (v2010) in the test environment. There were 3,688 stillbirths registered in England and Wales in Of these, 3,632 were fully coded using both ICD 10 versions (98.5 per cent). The remaining 56 stillbirths went to inquest and were coded manually using ICD 10 v and were not coded again for ICD 10 v2010.there were 2,251 neonatal deaths registered in England and Wales in 2009 and all were fully coded on both versions. Deaths from 2009 were chosen because this was the most recent published data year available. Results The number of mentions varied between 1 and 7 for stillbirths and 1 and 10 for neonatal deaths. As expected, the vast majority of codes were unchanged at the chapter and block level. Known code changes relevant for stillbirths and neonates are highlighted below. XV Pregnancy, Childbirth and the Puerperium (Codes O00 O99) No new codes or code changes in ICD 10 v2010 concerned this chapter. XVI Certain Conditions Originating in the Perinatal Period (Codes P00 P96) In the P91 group Other disturbances of cerebral status of newborn, a new code has been introduced: P91.6 Hypoxic ischaemic encephalopathy of newborn. Previously, this disorder was coded in P21.9 Birth asphyxia, unspecified. Other mentions of anoxia, asphyxia and hypoxia not otherwise specified still code to P21.9. This change will not affect the ONS Classification where group P200 P219 and group P910 P919 were both included in the Asphyxia, anoxia or trauma cause group. Office for National Statistics Statistical Bulletin 3

4 XVII Congenital Malformations, Deformations and Chromosomal Abnormalities (Codes Q00 Q99) One amendment concerns a rare congenital heart defect. Eisenmenger s defect is still coded to Q21.8 but Eisenmenger s syndrome or complex is coded to I27.8 Other pulmonary heart diseases. In 2009 there were no stillbirths or neonatal deaths coded to this rare congenital condition. Other minor amendments in this chapter did not have an impact on the stillbirths or neonatal deaths. XVIII Symptoms, Signs and Abnormal Clinical and Laboratory Findings, not elsewhere classified: code block Ill-defined and unknown causes of mortality (R95 R99) There are no changes to code R95 Sudden Infant Death Syndrome. Deaths so coded have been included with v code R99 Other ill-defined and unspecified causes of mortality to produce reports on Unexplained deaths in infancy. In ICD 10 v2010, this code is further divided. The undetermined and unspecified causes of death still go to code R99 but deaths of unknown cause go to new code R97. To further clarify this distinction, R99 includes deaths where the cause cannot be determined due to the circumstances (for example, only a skeleton was found) and deaths of natural causes though unspecified. R97 includes deaths where the aetiology remained undetermined despite medical investigations. This distinction will be further explored when the deaths occurring in 2011 and coded to ICD 10 v2010 are reported for the Unexplained deaths in infancy report. Future work ONS introduced the new version of the ICD 10 software for all deaths that are registered from January 2011 onwards. Infant and perinatal mortality statistics by ONS Classification of cause of death for the 2011 data year coded using ICD 10 v 2010 are expected to be published in autumn While this bulletin has highlighted the main changes relevant for perinatal mortality, any impact of these changes on the ONS cause groups will be explained when these statistics are published. Office for National Statistics Statistical Bulletin 4

5 Background Notes 1. A Bridge coding analysis of the impact on all deaths at 28 days and over is also available on the ONS website at: 2. All figures in this bulletin are based on 2009 death registrations data for England and Wales. 3. Examples of the stillbirth certificate (Annex A) and the neonatal death certificate (Annex B) can be found in the ONS publication Mortality statistics: Childhood, infant and perinatal, available on the ONS website at: 4. A brief description of the ONS cause groups can be found in Notes and definitions and the list of ICD 10 codes assigned to each group can be found in Annex J for stillbirths and Annex K for neonatal deaths in the ONS publication Mortality statistics: Childhood, infant and perinatal, available on the ONS website at: childhood--infant-and-perinatal/2009/index.html 5. Details of the policy governing the release of new data are available from the Media Relations Office. 6. National Statistics are produced to high professional standards set out in the Code of Practice for Official Statistics. They undergo regular quality assurance reviews to ensure that they meet customer needs. They are produced free from any political interference. Crown copyright References 1 World Health Organisation (1977) Manual of the international statistical classification of diseases, injuries, and causes of death, Volume 1. World Health Organization: Geneva. 2 Dattani, N. and Rowan, S. (2002) Causes of neonatal deaths and stillbirths: a new hierarchical classification in ICD 10, Health Statistics Quarterly 15 pp 16 22, available on the Office for National Statistics website at: autumn-2002/index.html 3 Wigglesworth, J.S. (1980) Monitoring perinatal mortality. A pathophysiological approach, Lancet 2 pp Issued by: Office for National Statistics, Government Buildings, Cardiff Road, Newport NP10 8XG Media contact: Tel: Media Relations Office Emergency on-call media.relations@ons.gsi.gov.uk Statistical contact: Tel: Julie Messer Office for National Statistics Statistical Bulletin 5

6 Website: Office for National Statistics Statistical Bulletin 6