Record-linkage methodology for prescribing research

Are women with major depression in pregnancy identifiable in population health data?

BACKGROUND

Although record linkage of routinely collected health datasets is a valuable research resource, most datasets are established for administrative purposes and not for health outcomes research. In order for meaningful results to be extrapolated to specific populations, the limitations of the data and linkage methodology need to be investigated and clarified. It is the objective of this study to investigate the differences in ascertainment which may arise between a hospital admission dataset and a dispensing claims dataset, using major depression in pregnancy as an example. The safe use of antidepressants in pregnancy is an ongoing issue for clinicians with around 10% of pregnant women suffer from depression. As the birth admission will be the first admission to hospital during their pregnancy for most women, their use of antidepressants, or their depressive condition, may not be revealed to the attending hospital clinicians. This may result in adverse outcomes for the mother and infant.

METHODS

Population-based de-identified data were provided from the Western Australian Data Linkage System linking the administrative health records of women with a delivery to related records from the Midwives' Notification System, the Hospital Morbidity Data System and the national Pharmaceutical Benefits Scheme dataset. The women with depression during their pregnancy were ascertained in two ways: women with dispensing records relating to dispensed antidepressant medicines with an WHO ATC code to the 3rd level, pharmacological subgroup, 'N06A Antidepressants'; and, women with any hospital admission during pregnancy, including the birth admission, if a comorbidity was recorded relating to depression.

RESULTS

From 2002 to 2005, there were 96698 births in WA. At least one antidepressant was dispensed to 4485 (4.6%) pregnant women. There were 3010 (3.1%) women with a comorbidity related to depression recorded on their delivery admission, or other admission to hospital during pregnancy. There were a total of 7495 pregnancies identified by either set of records. Using data linkage, we determined that these records represented 6596 individual pregnancies. Only 899 pregnancies were found in both groups (13.6% of all cases). 80% of women dispensed an antidepressant did not have depression recorded as a comorbidity on their hospital records. A simple capture-recapture calculation suggests the prevalence of depression in this population of pregnant women to be around 16%.

CONCLUSION

No single data source is likely to provide a complete health profile for an individual. For women with depression in pregnancy and dispensed antidepressants, the hospital admission data do not adequately capture all cases.

Association between allopurinol and mortality in heart failure patients: a long-term follow-up study

AIMS

The aim of the study was to explore the long-term effect of allopurinol on mortality and cardiovascular hospitalisations in heart failure (HF) patients.

METHODS

This is a population-based cohort study using a record-linkage database in Tayside, Scotland. A total of 4785 HF patients (4260 non-users, 267 incident users and 258 prevalent users) were studied between 1993 and 2002.

RESULTS

Compared with non-users, low-dose users in the incident group had a significant increased risk of all-cause mortality, cardiovascular mortality and cardiovascular recurrence (adjusted HR, 1.60, 95%CI 1.26-2.03; 1.70, 1.29-2.23 and 1.44, 1.01-2.07). For the prevalent users, the adjusted HR were 1.27, 0.98-1.64; 1.43, 1.07-1.90 and 1.27, 0.91-1.76 respectively. There was no increased risk of outcome for high-dose users when compared with non-users (adjusted HR, 1.18, 0.84-1.66; 1.14, 0.76-1.71 and 1.36, 0.88-2.10 for the incident users, and 0.86, 0.64-1.15; 0.90, 0.64-1.26; and 1.27, 0.93-1.74 for the prevalent users respectively). High-dose allopurinol was associated with reduced risk of all-course mortality for prevalent users when compared with low-dose (adjusted HR 0.65, 95%CI 0.42-0.99).

CONCLUSIONS

The prevalent high-dose allopurinol use had a lower risk of mortality than the prevalent low-dose use suggesting that allopurinol may be of benefit in HF patients.

Pharmacovigilance in pregnancy using population-based linked datasets

PURPOSE

National dispensing data for subsidized prescription medicines have recently been approved for linkage to the population-based health datasets in Western Australia (WA), creating the capacity to study how these medicines are used and their impact on pregnancy outcomes.

METHODS

Pregnancy events were identified in the Hospital Morbidity Data System from 2002 to 2005 (N = 164,278 admissions; N = 98,265 women) and linked to the midwives' notification system (MNS), the registry of births and deaths, the Western Australian birth defects registry and the pharmaceutical benefit scheme. Dispensing records were extracted for each pregnancy event (N = 1,276,084 dispenses).

RESULTS

There were 106,074 births, 1527 ectopic pregnancies and 25,180 terminations of pregnancy. Dispensed medicines were linked to 28.0% of the pregnancy events. Multiple birth pregnancies were 50% more likely to be dispensed a medicine in the first trimester. As parity increased, so did the likelihood of a medicine being dispensed in pregnancy. Women who were dispensed a medicine were twice as likely to smoke during pregnancy and were 14% more likely to have a registered birth defect. During the first trimester, medicines from category D or X of the risk of drug use in pregnancy were dispensed to 2.1% of all pregnancy events. The WHO ATC 'Psychoanaleptics' category was dispensed to 3.8% of all pregnancy events.

CONCLUSION

Linkage of dispensing data to pregnancy events is feasible and this approach to post-marketing surveillance will add to the resources available in Australia to investigate pregnancy outcomes in relation to the safe use of prescribed medicines in pregnancy.

Developing prevalence-based prescribing units for analysing variations in general practitioner prescribing: a case study using statins

OBJECTIVE

To develop regionally specific prevalence-, age- and sex-standardized prescribing units (PASS-PUs) and to relate these to statin prescribing.

DESIGN

Cross-sectional.

SETTING

Ninety-four general practitioner (GP) practices within one health authority in the north-west of England.

MAIN OUTCOME MEASURES

Comparisons between specific therapeutic group age-sex-related prescribing units (STAR-PUs) and PASS-PUs for statin prescribing.

RESULTS

STAR-PUs and PASS-PUs were calculated for all GP practices and there was a high degree of correlation (Spearman's rank coefficient 0.88; P < 0.001). Using actual prescribing data for statins for a 12-month period, a statistically significant correlation was found between net ingredient cost per patient and STAR-PUs per patient (Spearman's rank coefficient 0.36; P < 0.01). However, the correlation between average daily quantities per patient and PASS-PUs per patient was not statistically significant. A scatter plot revealed a pattern whereby GP practices with high proportions of patients aged over 75 years exhibited low statin prescribing in relation to the expected prevalence of treated coronary heart disease (CHD) in their patient population.

CONCLUSIONS

Low weightings for patients aged over 75 years in calculating STAR-PUs lead to a much lower number of prescribing units within GP practice populations when compared with PASS-PUs. Current statin prescribing across GP practices in this study correlates with national prescribing cost patterns (as measured by STAR-PUs) although not with expected prevalence of treated CHD (as measured by PASS-PUs). PASS-PUs reflect prevalence of treated CHD and may therefore be used to monitor and predict GP prescribing arising from the implementation of the National Service Framework targets for CHD. In addition, PASS-PUs maybe derived for a wide range of therapeutic areas.