There was no significant colocalization between MMP-9-positive cells and podocytes

d comparator subjects. This supports a causative association between AS and NL. To our knowledge this is the first study to assess the risk of NL diagnosis in AS patients compared to matched general population subjects based on nationwide prospective data. This association has previously been suggested by a few studies. However these studies were based on cross-sectional data in selected AS populations diagnosed and treated at single outpatient centre. Sample size was small. One study lacked control subjects, while the other 2 included small control groups selected in the same setting and without any matching. The Swedish National Patient Register consisting of the Inpatient Register and the Outpatient Register is a substantial data source in this study. All physicians in the country working in both publicly funded as well as private healthcare units are obliged to report data, including personal identity number and ICD-coded diagnosis, on all in-patient and specialist out-patient visits. Evaluations of data in the Inpatient Register have shown validity between 85 95% across different diagnoses and coverage of more than 99%. 10 / 14 Kidney Stones in Ankylosing Spondylitis Regarding data on specialist outpatient visits, the overall coverage of 80% is somewhat lower. This is primarily explained by missing data from private caregivers, whereas coverage from public non primary care outpatient units is almost 100%. Thus nationwide register-based studies like the present have the apparent strength of being population-based reducing the risk of selection bias. In addition, the large sample size allows for adjustment and sensitivity analyses. However some degree of residual confounding and bias cannot be ruled out. Selection of AS patients in this study is based on ICD-codes recorded by a specialist in rheumatology or internal medicine. This might create a selection bias towards more severe cases being included, while missing patients with mild disease who are managed entirely at primary care units. However, according to a previous study in the same setting, this is a minor problem and would only increase the number of PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19683642 cases by less than 4%, at the expense of a larger degree of misclassification. Regarding the case definitions of AS used in this study PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19682619 unpublished data and results from southern Sweden suggest that misclassification occurs in less than 10%. Concerning comorbidities such as acute coronary events, misclassification is estimated to be less than 5%. Data on NL as well as comorbidities in this study is based on ICD-codes recorded by physicians at inpatient and outpatient somatic care units irrespective of speciality. Thus our results do not account for patients who are exclusively diagnosed and treated in primary care units. This may be the case for some of the relevant comorbidities such as obesity, DM, hyperlipidaemia and hypertension. In addition some relevant comorbidities such as calcium order BQ 123 metabolic disorders and renal disease may remain undiagnosed/subclinical. Regarding NL diagnosis we assume that a high proportion of all patients with symptomatic and thus significant NL are managed in inpatient or outpatient specialist care units and thus have a recorded diagnosis of NL. However we cannot rule out the possibility, that a proportion of patients with asymptomatic or mild NL passing spontaneously are diagnosed and treated entirely in primary care. Thus, our data could have been affected by differential ascertainment of both outcome