Wednesday, August 29, 2012

Albumin/ creatinine ratio, false positives and false negatives





Albumin/ creatinine ratio  - < 30 is a screening test generally associated with normal kidney function.
"Confirmed test " greater than 30  is a marker of increased risk of developing kidney disease.

       One problem with this test is false positives and negatives.

The test may be falsely elevated by high glucose levels , Exercise within the last 24 hours , infection , fever , high blood pressure .
 A recent follow up reports false negatives in 24% of patients with type 1 diabetes  who progressed to more severe kidney damage. The good news is that it was a useful screening tool and provided comfort in 76% of the patients . The high false negative results provides support for a better screening test such as the one we mentioned in yesterdays post. *( reference below)

The American diabets Association 2012 guidelines recommend:
" Because of the variability in urinary albumin excretion , 2 or 3 specimens collected within a 3 to 6 month period before considering a patient crossed one of the diagnostic thresholds "

more on Albumin /creatinine ratios tomorrow.

Have fun , Be Smart and remember Diabetes care is a winnable  game of numbers
David Calder,MD

* Development and Progression of Renal Insufficiency With and Without Albuminuria in Adults With Type 1 Diabetes in the Diabetes Control and Complications Trial and the Epidemiology of Diabetes Interventions and Complications Study
Molitch ME, Steffes M, Sun W, Rutledge B, Cleary P, de Boer IH, Zinman B, Lachin J, Epidemiology of Diabetes Interventions and Complications Study Gro - Diabetes Care (2010)

Bottom Line: Of these, 20 (24%) had AER <30 mg/24 h at all prior evaluations, 14 (16%) had developed microalbuminuria (AER 30-300 mg/24 h) before they reached stage 3 chronic kidney disease, and 54 (61%) had macroalbuminuria (AER >300 mg/24 h) before they reached stage 3 chronic kidney disease.Macroalbuminuria is associated with a markedly increased rate of fall in eGFR (5.7%/year vs. 1.2%/year with AER <30 mg/24 h, P < 0.0001) and risk of eGFR <60 ml/min/1.73 m(2) (adjusted hazard ratio 15.3, P < 0.0001), whereas microalbuminuria had weaker and less consistent effects on eGFR.Macroalbuminuria was a strong predictor of eGFR loss and risk of developing sustained eGFR <60 ml/min/1.73 m(2).However, screening with AER alone would have missed 24% of cases of sustained impaired eGFR.
Affiliation: Northwestern University, Chicago, Illinois, USA. cleary@biostat.bsc.gwu.edu
Abstract: This multicenter study examined the impact of albumin excretion rate (AER) on the course of estimated glomerular filtration rate (eGFR) and the incidence of sustained eGFR <60 ml/min/1.73 m(2) in type 1 diabetes up to year 14 of the Epidemiology of Diabetes Interventions and Complications (EDIC) study (mean duration of 19 years in the Diabetes Control and Complications Trial [DCCT]/EDIC).Urinary albumin measurements from 4-h urine collections were obtained from participants annually during the DCCT and every other year during the EDIC study, and serum creatinine was measured annually in both the DCCT and EDIC study. GFR was estimated from serum creatinine using the abbreviated Modification of Diet in Renal Disease equation.A total of 89 of 1,439 subjects developed an eGFR <60 ml/min/1.73 m(2) (stage 3 chronic kidney disease on two or more successive occasions (sustained) during the DCCT/EDIC study (cumulative incidence 11.4%). Of these, 20 (24%) had AER <30 mg/24 h at all prior evaluations, 14 (16%) had developed microalbuminuria (AER 30-300 mg/24 h) before they reached stage 3 chronic kidney disease, and 54 (61%) had macroalbuminuria (AER >300 mg/24 h) before they reached stage 3 chronic kidney disease. Macroalbuminuria is associated with a markedly increased rate of fall in eGFR (5.7%/year vs. 1.2%/year with AER <30 mg/24 h, P < 0.0001) and risk of eGFR <60 ml/min/1.73 m(2) (adjusted hazard ratio 15.3, P < 0.0001), whereas microalbuminuria had weaker and less consistent effects on eGFR.Macroalbuminuria was a strong predictor of eGFR loss and risk of developing sustained eGFR <60 ml/min/1.73 m(2). However, screening with AER alone would have missed 24% of cases of sustained impaired eGFR.



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Your comments and questions are appreciated. David Calder,MD