Defining Baseline Creatinine for Identification of AKI in Population-Based Laboratory Databases: A Danish Nationwide Cohort Study

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Abstract

Background

The baseline creatinine level is central in the Kidney Disease Improving Global Outcomes (KDIGO) criteria of AKI, but baseline creatinine is often inconsistently defined or unavailable in AKI research. We examined the rate, characteristics, and 30-day mortality of AKI in five AKI cohorts created using different definitions of baseline creatinine.

Methods

This nationwide cohort study included all individuals aged ≥18 years in Denmark with a creatinine measurement in 2017. Applying the KDIGO criteria, we created four AKI cohorts using four different baseline definitions (most recent, mean, or median value of outpatient creatinine 365–368 days before, or median value 90–98 days before, if available, otherwise median value 365–391 days before) and one AKI cohort not using a baseline value. AKI rate and the distribution of age, sex, baseline creatinine, and comorbidity were described for each AKI cohort, and the 30-day all-cause mortality was estimated using the Kaplan–Meier method.

Results

The study included 2,095,850 adults with at least one creatinine measurement in 2017. The four different baseline definitions identified between 61,189 and 62,597 AKI episodes. The AKI rate in these four cohorts was 13–14 per 1000 person-years, and 30-day all-cause mortality was 17%–18%. The cohort created without using a baseline creatinine included 37,659 AKI episodes, corresponding to an AKI rate of 8.2 per 1000 person-years and a 30-day mortality of 23%. All five cohorts were similar regarding age, sex, and comorbidity.

Conclusions

In a population-based setting with available outpatient baseline creatinine, different baseline creatinine definitions revealed comparable AKI cohorts, whereas the lack of a baseline creatinine when defining AKI led to a smaller AKI cohort with a higher mortality. These findings underscore the importance of availability and consistent use of an outpatient baseline creatinine, particulary in studies of community-acquired AKI.

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Most cited references 24

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A new equation to estimate glomerular filtration rate.

Andrew Levey, Lesley Stevens, Christopher H Schmid … (2009)

Equations to estimate glomerular filtration rate (GFR) are routinely used to assess kidney function. Current equations have limited precision and systematically underestimate measured GFR at higher values. To develop a new estimating equation for GFR: the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Cross-sectional analysis with separate pooled data sets for equation development and validation and a representative sample of the U.S. population for prevalence estimates. Research studies and clinical populations ("studies") with measured GFR and NHANES (National Health and Nutrition Examination Survey), 1999 to 2006. 8254 participants in 10 studies (equation development data set) and 3896 participants in 16 studies (validation data set). Prevalence estimates were based on 16,032 participants in NHANES. GFR, measured as the clearance of exogenous filtration markers (iothalamate in the development data set; iothalamate and other markers in the validation data set), and linear regression to estimate the logarithm of measured GFR from standardized creatinine levels, sex, race, and age. In the validation data set, the CKD-EPI equation performed better than the Modification of Diet in Renal Disease Study equation, especially at higher GFR (P < 0.001 for all subsequent comparisons), with less bias (median difference between measured and estimated GFR, 2.5 vs. 5.5 mL/min per 1.73 m(2)), improved precision (interquartile range [IQR] of the differences, 16.6 vs. 18.3 mL/min per 1.73 m(2)), and greater accuracy (percentage of estimated GFR within 30% of measured GFR, 84.1% vs. 80.6%). In NHANES, the median estimated GFR was 94.5 mL/min per 1.73 m(2) (IQR, 79.7 to 108.1) vs. 85.0 (IQR, 72.9 to 98.5) mL/min per 1.73 m(2), and the prevalence of chronic kidney disease was 11.5% (95% CI, 10.6% to 12.4%) versus 13.1% (CI, 12.1% to 14.0%). The sample contained a limited number of elderly people and racial and ethnic minorities with measured GFR. The CKD-EPI creatinine equation is more accurate than the Modification of Diet in Renal Disease Study equation and could replace it for routine clinical use. National Institute of Diabetes and Digestive and Kidney Diseases.

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The Danish National Patient Registry: a review of content, data quality, and research potential

Morten Schmidt, Sigrun Alba Johannesdottir Schmidt, Jakob Sandegaard … (2015)

Background The Danish National Patient Registry (DNPR) is one of the world’s oldest nationwide hospital registries and is used extensively for research. Many studies have validated algorithms for identifying health events in the DNPR, but the reports are fragmented and no overview exists. Objectives To review the content, data quality, and research potential of the DNPR. Methods We examined the setting, history, aims, content, and classification systems of the DNPR. We searched PubMed and the Danish Medical Journal to create a bibliography of validation studies. We included also studies that were referenced in retrieved papers or known to us beforehand. Methodological considerations related to DNPR data were reviewed. Results During 1977–2012, the DNPR registered 8,085,603 persons, accounting for 7,268,857 inpatient, 5,953,405 outpatient, and 5,097,300 emergency department contacts. The DNPR provides nationwide longitudinal registration of detailed administrative and clinical data. It has recorded information on all patients discharged from Danish nonpsychiatric hospitals since 1977 and on psychiatric inpatients and emergency department and outpatient specialty clinic contacts since 1995. For each patient contact, one primary and optional secondary diagnoses are recorded according to the International Classification of Diseases. The DNPR provides a data source to identify diseases, examinations, certain in-hospital medical treatments, and surgical procedures. Long-term temporal trends in hospitalization and treatment rates can be studied. The positive predictive values of diseases and treatments vary widely (<15%–100%). The DNPR data are linkable at the patient level with data from other Danish administrative registries, clinical registries, randomized controlled trials, population surveys, and epidemiologic field studies – enabling researchers to reconstruct individual life and health trajectories for an entire population. Conclusion The DNPR is a valuable tool for epidemiological research. However, both its strengths and limitations must be considered when interpreting research results, and continuous validation of its clinical data is essential.

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The Danish Civil Registration System as a tool in epidemiology.

Morten Schmidt, Lars Østergaard Pedersen, Henrik Toft Sørensen (2014)

The methodological advances in epidemiology have facilitated the use of the Danish Civil Registration System (CRS) in ways not previously described systematically. We reviewed the CRS and its use as a research tool in epidemiology. We obtained information from the Danish Law on Civil Registration and the Central Office of Civil Registration, and used existing literature to provide illustrative examples of its use. The CRS is an administrative register established on April 2, 1968. It contains individual-level information on all persons residing in Denmark (and Greenland as of May 1, 1972). By January 2014, the CRS had cumulatively registered 9.5 million individuals and more than 400 million person-years of follow-up. A unique ten-digit Civil Personal Register number assigned to all persons in the CRS allows for technically easy, cost-effective, and unambiguous individual-level record linkage of Danish registers. Daily updated information on migration and vital status allows for nationwide cohort studies with virtually complete long-term follow-up on emigration and death. The CRS facilitates sampling of general population comparison cohorts, controls in case-control studies, family cohorts, and target groups in population surveys. The data in the CRS are virtually complete, have high accuracy, and can be retrieved for research purposes while protecting the anonymity of Danish residents. In conclusion, the CRS is a key tool for epidemiological research in Denmark.