Are prediction equations for glomerular filtration rate useful for the long-term monitoring of type 2 diabetic patients? Ne´ stor Fontsere´, Isabel Salinas, Jordi Bonal, Beatriz Baye´ s, Joaquim Riba, Ferran Torres, Jose Rios, Ana Sanmartı´ and Ramo´ n Romero Universidad Auto´ noma de Barcelona, Barcelona, Spain Nephrol Dial Transplant (2006) 21: 2152–2158

Background Type 2 diabetes –one of the most frequent causes of chronic renal insufficiency Purified monitoring of renal function –reducing associated comorbidity factors Isotopic determination of the glomerular filtration rate (GFR) –gold standard method –expensive option

Aim Renal function & annual slope for GFR in type 2 diabetes Isotopic method Different prediction equations  Modification of diet in renal disease(MDRD)  Simplified MDRD (sMDRD)  Cockcroft–Gault formula (CG)  Reciprocal of creatinine  Creatinine clearance using 24 h urine collection

Methods Study population –October 1989 ~ November 2003 –87 patients with type 2 DM (53 women/34 men). Demographic: age, sex Anthropometric: weight, height, body surface Biochemical: serum & urinary creatinine, urea nitrogen, albumin –Three study subgroups Normal renal function CKD stages 2–3 Hyperfiltration - GFR: 90 ~ 140 ml/min/1.73m 2 - GFR > 140 ml/min/1.73m 2 - GFR: 30 ~ 89 ml/min/1.73m 2

Study design and methods –Isotopic GFR intravenous injection of 30–50 mCi 125 I-iothalamate –Other prediction equations  CG Men: (140 - age) x weight (kg) / 72 x SCr. Women: [(140 – age) x weight (kg) / 72 x SCr] x 0.85  MDRD 170 x (SCr) x (age) x (BUN) x (Alb) x (0.762)female sex  sMDRD 186 x (SCr) x (age) x (0.762)female sex  Reciprocal of creatinine 100/SCr  Creatinine clearance Ucr x Vo/min (diuresis 24 h/1440 min) / (SCr) SCr, serum creatinine (mg/dl): UCr, 24 h urinary creatinine (mg/dl): Vo, urine volume BUN, blood urea nitrogen [urea (mg/dl)/2.14]: Alb, serum albumin (g/dl)

Table 1. Clinical and analytical data of 87 type 2 DM patients at baseline and the last observation during the follow-up period Results

Table 2. Comparison of prediction equations in normal renal function and hyperfiltration groups of type 2 DM patients during the follow-up period Normal renal function group: 47 patients, Mean age of 58 ± 8.5 years Hyperfiltration group: 27 patients, Mean age of 52 ± 9.2 years

Table 3. Comparison of prediction equations in CKD stages 2–3 of type 2DM patients during the follow-up period CKD stages 2–3 group: 13 patients, Mean age of 63 ± 7.9 years

Fig. 1. Cross- sectional comparison of standardized iothalamate clearance with five indirect methods of measuring renal function in 87 type 2 diabetic patients MDRD: to - 4.1% sMDRD: to - 0.4% CG: - 63 to 3.5% Reciprocal of creatinine : to 50.1% Creatinine clearance : to 56.6%.

Conclusion Excessive underestimation of renal function none of the prediction equations MDRD equation : GFR estimation Normal renal function & Hyperfiltration groups CKD stages 2–3 with mean serum creatinine 1.5 mg/dl