Definition of chronic kidney disease and measurement of kidney function in original research papers: a review of the literature.

BACKGROUND

Over the past decade, chronic kidney disease (CKD) has become an area of intensive clinical and epidemiological research. Despite the clarity provided by the Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines, there appears to be within the CKD research literature significant disagreement on how to define CKD and measure kidney function.

METHODS

The objectives of this study were to investigate the variety of methods used to define CKD and to measure kidney function in original research papers as well as to investigate whether the quality of the journal had any effect on the quality of the methodology used. This was a descriptive review and not a meta-analysis. Information was extracted from each article including publication details (including the journal's impact factor), definition of CKD, method used to estimate kidney function and quantity of serum creatinine readings used to define CKD. An electronic search of MEDLINE through OVID was completed using the search term CKD. The search was limited to articles in English published in 2009. Studies were included in the review only if they were original research articles including patients with CKD. Articles were excluded if they reported data from a paediatric population, a population solely on dialysis or if there was no full-text access through OVID. Each article was assessed for quality with respect to using KDOQI CKD definition criteria. A description of the pooled data was completed and chi-square tests were used to investigate the relation between article quality and journal quality. Analysis was carried out using SPSS (15.0) and a P-value of <0.05 was considered to indicate statistical significance.

RESULTS

The final review included 301 articles. There were a variety of methods used to define CKD in original research articles. Less than 20% (n = 59) of the articles adhered to the established international criteria for defining CKD. The majority of articles (52.1%) did not indicate the quantity of serum creatinine measurements used to define CKD. The impact factor or specialist nature of the scientific journal appears to have no bearing on whether or not published articles use the gold standard KDOQI guidelines for labelling a patient with a diagnosis of CKD.

CONCLUSIONS

This review of literature found that a variety of definitions are being used in original research articles to define CKD and measure kidney function which calls into question the validity and reliability of such research findings and associated clinical guidelines. International consensus is urgently required to improve validity and generalizability of CKD research findings.