2 d) Proteinuria as a screening tool
Proteinuria and impaired renal function are both strong predictors for progressive renal failure and perhaps more importantly for cardiovascular disease (Halbesma et al, 2006). Screening for renal disease may make sense as interventions such ACE inhibition and control of cardiovascular risk factors in at risk subjects is effective in prevention or retardation of progressive renal impairment and avoidance of cardiovascular complications. Nevertheless there is ongoing debate on the cost effectiveness of population based screening for renal disease (de Jong et al, 2006).
Detection of chronic kidney disease (CKD) requires quantitative evaluation of both renal function (for stages 2 to 5) and proteinuria (for stages 1 and 2). Presence of proteinuria is an independent marker of progression of renal failure at all levels of renal function (Halbesma et al, 2006). Cost effectiveness may be improved by confining screening to high risk populations identified as having predisposition for CKD or individuals having abnormal results using cheaper “pre-screening” tests such as dip stick urinalysis.
Bang et al. (2007) have developed a simple model for prediction of occult CKD based upon demographic parameters and the presence of various health conditions such as hypertension, diabetes and peripheral vascular disease. Iseki (2006) and Iseki et al (2007, 2007) have examined mass screening data from Okinawa and have shown changes in the demographic characteristics of Japanese patients with CKD between 1993 and 2003. Dipstick positive proteinuria and both high systolic and diastolic blood pressure were useful to identify individuals at risk of developing progressive CKD. Another study (Ishizaka et al, 2007) demonstrated that overweight and obesity were strong independent predictors of increased risk of CKD in Japanese individuals.
Albuminuria of greater than 30 mg/day is one of the criteria for CKD but this requires collection of a 24 hour urine sample which is expensive, inconvenient and may lead to inaccuracy due to incomplete collection. Two studies have examined the effectiveness of pre screening using spot urine sample for albumin concentration or albumin creatinine ratios (Jafar et al, 2007; Gansevoort et al, 2005). Of note, both studies found the diagnostic performance of assessment of the albumin concentration and the albumin:creatinine ratio comparable. From an economic perspective this is an important observation. In order to keep costs involved in mass screening for micro-albuminuria as low as possible, it was therefore proposed that pre-screening should take place by measuring only albumin concentration in a spot morning urine sample.
Best practice for screening for renal disease in the UK is under discussion. The National Institute for Clinical Excellence have produced draft guidance (NICE, 2008) which is published for consultation on their web site. Current recommendations include the use of an albumin creatinine ratio to quantify proteinuria and screening for CKD using the MDRD formula in all people with diabetes, hypertension, cardiovascular disease, family history of CKD stage 5, known structural renal tract disease such as stones, incidental urine sediment abnormality or know use of nephrotoxic drugs.
References
1. Halbesma N, Kuiken DS, Brantsma AH, Bakker S, et al. Macroalbuminuria is a better risk marker than low estimated GFR to identify individuals at risk for accelerated GFR loss in population screening. Journal of the American Society of Nephrology 2006;17(9):2582-90. [PubMed]
2. de Jong PE, Halbesma N, Gansevoort RT. Screening for early chronic kidney disease - What method fits best? Nephrology Dialysis Transplantation 2006;21(9):2358-61. [PubMed]
3. Bang H, Vupputuri S, Shoham D, A, Klemmer P, J, et al. SCreening for Occult REnal Disease (SCORED): A simple prediction model for chronic kidney disease. Archives of Internal Medicine 2007;167(4):374-81. [PubMed]
4. Iseki K. Screening for renal disease - What can be learned from the Okinawa experience. Nephrology Dialysis Transplantation 2006;21(4):839-43. [PubMed]
5. Iseki K, Kohagura K, Sakima A, Iseki C, Kinjo K, Ikemiya Y, et al. Changes in the demographics and prevalence of chronic kidney disease in Okinawa, Japan (1993 to 2003). Hypertens Res 2007 Jan;30(1):55-62. [PubMed]
6. Iseki K, Iseki C, Ikemiya Y, Kinjo K, Takishita S. Risk of developing low glomerular filtration rate or elevated serum creatinine in a screened cohort in Okinawa, Japan. Hypertens Res 2007 Feb;30(2):167-74. [PubMed]
7. Ishizaka N, Ishizaka Y, Toda E, Koike K, Seki G, Nagai R, et al. Association between obesity and chronic kidney disease in Japanese: differences in gender and hypertensive status? Hypertens Res 2007 Nov;30(11):1059-64. [PubMed]
8. Jafar TH, Chaturvedi N, Hatcher J, Levey AS. Use of albumin creatinine ratio and urine albumin concentration as a screening test for albuminuria in an Indo-Asian population. Nephrology Dialysis Transplantation 2007;22(8):2194-200. [PubMed]
9. Gansevoort RT, Verhave JC, Hillege HL, et al. for the PREVEND Study Group. The validity of screening based on spot morning urine samples to detect subjects with microalbuminuria in the general population. Kidney Int Suppl (2005) 94:S28–S35. [PubMed]
10. NICE (full guideline due in September 2008): Early identification and management of adults with chronic kidney disease in primary and secondary care. [Consultation documents]
Link to 2008 NICE Chronic Kidney Disease guideline
Link to National Knowledge Week contents page
