Clinical Correlates of Functional Status in Patients With Chronic Renal Insufficiency

Patients with end-stage renal disease (ESRD) are known to have significantly reduced functional abilities, as measured by the Sickness Impact Profile (SIP). We investigated the clinical correlates with SIP scores in a cohort of patients with lesser degrees of renal dysfunction recruited from an academic general medicine practice (mean calculated creatinine clearance, 25 mL/min). Of 603 eligible patients with chronic renal insufficiency (CRI) defined as a serum creatinine greater than 1.5 mg/dL and a calculated creatinine clearance less than 50 mL/min on two occasions more than 6 months apart, 360 (60%) agreed to participate. These patients were primarily elderly (mean age, 69 years) black (83%), women (69.2%), with an average of 6 years of education and a household income of $400 to $800 per month; 92% had hypertension and 57% had diabetes. The SIP was administered in-home by trained interviewers. Independent variables included demographic data, education, income, and medications (via interviewers), vital signs taken by a renal nurse, and diagnostic test results and diagnoses from patient’s computerized records. The total SIP score was the dependent variable, and its physical and psychosocial subscales were also investigated. Variables with univariate correlations with total SIP (P < 0.05) were included in a multiple regression analysis. All variables with a multivariable P value less than 0.10 were included in the final model. The mean SIP score was 24.5 ± 15.6, higher than that found in patients on dialysis. Significant (P < 0.05) independent correlates with higher SIP scores (greater disability) were lower educational level and income, prior diagnoses of coronary artery disease and stroke, and lower serum albumin. Borderline correlations (0.05 < P < 0.10) with higher SIP scores were found for white patients and women, the diagnoses of congestive heart failure and osteoarthritis, and lower serum sodium. The effect of these variables was found mostly in the SIP physical subscale. No effect of generally used measures of renal function (blood urea nitrogen [BUN], creatinine, creatinine clearance) was found. Patients with CRI are significantly disabled even before the development of ESRD, but in this population, the disability is correlated mostly with socioeconomic and comorbid conditions, not renal function. This model may help identify a subgroup of patients who would benefit from intensive outpatient management to improve function and prevent morbid events.