The Modification of Diet in Renal Disease Trial is a multicenter randomized clinical trial for men and women aged 18-70 years with chronic renal disease who are not on dialysis and who have not had a kidney transplant. Study participants are randomized in a 2 × 2 factorial design to diets containing different amounts of protein and phosphorus and to two levels of blood pressure control. The prescribed modifications differ depending on the level of a patient's kidney function. The primary outcome variable to compare diet or blood pressure groups is each patient's slope (or the change) in glomerular filtration rate (GFR) with time.

Selection of patients is conducted in two periods: a screening period for initial determination of eligibility and a 3-month baseline period. The baseline period is used to instruct patients about study procedures; to assess GFR and dietary protein intake; and to control blood pressure according to standard medical practice. GFR, dietary protein, and urinary protein must meet the eligibility criteria at the end of the baseline period before an individual can be randomized.

Two different strata or studies are used depending on the level of an individual's GFR at the end of the baseline period. Study A is for individuals with a GFR from 25 to 55 ml/min/1.73 m^2 and a usual dietary protein intake of at least 0.90 g/kg/day, where kg are standard body weight. Study B is for persons with a baseline GFR from 13 to 24 ml/min/1.73 m^2 and no specification of protein intake.

Individuals who are randomized in the trial are prescribed one of three diets and one of two target mean arterial blood pressure goals (MAP). MAP is a weighted average of the diastolic and systolic blood pressures (two-thirds diastolic plus one-third systolic). The goals depend on the person's age. The moderate goal of 107 mm Hg is equivalent to a blood pressure of 140/90 mm Hg, the usual limits of normal blood pressure. The low-MAP goal of 92 mm Hg is a more strict level of control than usually achieved, equivalent to, for example, 125/75 mm Hg.

Inclusion Criteria:

• Increased serum creatinine: Men: 1.4-7.0 mg/dl, Women: 1.2-7.0 mg/dl, or other objective evidence of kidney disease
• Mean arterial blood pressure <=125 mm Hg
• GFR 13-55 ml/min/1.73 m^2
• Urinary protein excretion <10 g/day
• Protein intake >0.90 g/kg/day if GFR 25-55 ml/min/1.73 m^2

Exclusion Criteria:

• Insulin-dependent diabetes or fasting serum glucose >200 mg/dl
• Patient on dialysis
• Kidney transplant recipient
• Lactating or pregnant woman or woman planning to become pregnant within the time frame of the study
• Doubtful compliance
• Body weight <80% or >160% of standard body weight
• Serum albumin <3.0 g/dl
• Selected renal disorders: Upper or lower urinary tract obstruction, Renal artery stenosis, Branched or staghorn calculi, Cystinuria
• Serious medical conditions: Malignancy (excluding skin cancer) within 1 year, Heart failure, New York Heart Association class 3 or 4, Lung disease, Liver disease, Gastrointestinal disease, Chronic systemic infections, including AIDS, Collagen vascular disease (other than rheumatoid arthritis), Frequent hospitalizations or disability
• Drugs: Immunosuppressive agents, Corticosteroids in excess of replacement dosage for 2 months per year or more, Gold or penicillamine within past month, Salicylates: more than 20 tablets per week, Other nonsteroidal antiinflammatory agents more than 3 times per week in past 2 months, Investigational drugs
• Allergy to iothalamate or iodine
• Inability or unwillingness to give consent

Data and samples are available at the National Institute of Diabetes Digestive and Kidney Diseases (NIDDK) Central Repository