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Who and how to screen for chronic kidney disease

Stein Hallan

MD PhD St Olav University Hospital
Trondheim, Norway
MAY 12th - Symposium 14 - HALL A1  11:30 - 12:30

The number of patients starting dialysis has increased more than five-fold during the last three decades representing an immense socioeconomic burden. Most of these patients suffer from chronic kidney disease (CKD), a group of kidney diseases caused by diabetes mellitus, hypertension, autoimmunity, atherosclerosis, or genetic disease. CKD is usually a silent, slowly progressing disease causing no symptoms until more than 80% of kidney function (measured as glomerular filtration rate, GFR) is lost. It is well documented that intervention during the early stages of CKD can reduce the rate of progression towards kidney failure. Since the publication of the US KDOQI guidelines on the classification of CKD in 2002, several studies based on this classification system have shown very high prevalence estimates of CKD in the general population (10-13%), and screening for CKD is therefore increasingly suggested. 
Screening the general population would be expensive and difficult to implement, so targeting more high risk subgroups is therefore advisable. Screening for kidney damage in patients with diabetes has long been recommended, and hypertensive patients are now also considered for kidney testing. This has been shown to be an efficient approach, but such a screening strategy would only detect half of all CKD patients. Many other “at-risk” subgroups have been suggested, but the screening strategy could end up too complicated for successful implementation. Inclusion of all subjects above age 55 has been found equally efficient and simpler. Pre-selection of subjects by home-testing of the urine is also suggested and have been applied on the entire population of the Netherlands.  
However, only a very small proportion of CKD cases progress to kidney failure. This implies that the current classification system, which is mainly based on categories of GFR, is not optimal. Proteinuria has long been recognized as a very important marker of kidney prognosis, but we do not yet know how to combine GFR and proteinuria optimally. Several other factors have also been identified as risk factors for CKD progression. A simple method for risk assessment analogous to the Framingham risk scores for coronary heart disease, are urgently needed. Hopefully new tests based on genetic information or specific urinary substances will bring this work forward.
In conclusion, although many kidney authorities advocate screening for CKD, the documentation do not convincingly fulfill all formal criteria needed for large-scale screening of the general population. This especially relate to the screening tests used. An extraordinary low false positive rate is needed as we, contrary to e.g. cancer screening programs, do not have the opportunity to refer subjects testing positive to an absolute confirmatory test. Randomized controlled trials comparing the benefits and cost in a population offered screening versus a population not offered screening is needed before we can conclude on CKD screening.