Efficacy of patient questionnaire in predicting renal dysfunction in outpatients older than 60 years of age prior to contrast-enhanced computed tomography.

INTRODUCTION: Contrast-induced nephropathy (CIN), a common iatrogenic cause of acute renal failure, is preventable. Identification of impaired renal function prior to intravenous contrast is important. Questionnaire screening has been useful to negate the need for cumbersome and costly renal function testing on all patients prior to contrast-enhanced CT (CECT). The Royal Australian and New Zealand College of Radiologists guidelines include age older than 60 as a risk marker requiring renal function testing. The aim of this retrospective study is to assess the efficacy of the pre-CT questionnaire in identifying patients with pre-existing renal impairment even in this older than 60 age group.

METHODS: All outpatients were given questionnaires containing 11 CIN risk markers prior to CECT. Radiographers documented age, gender, serum creatinine and/or estimated glomerulofiltration rate (eGFR mL/min/1.72 m(2) ) within 3 months of CT. Questionnaires of all patients older than 60 years were collated. The data was tabulated and analyzed. Incomplete questionnaires were excluded.

RESULTS: 134/171 (78.4%) patients had eGFR ≥ 60 and 37/171 (21.6%) had eGFR < 60, with 31/171 (18.1%) having eGFR between 30 and 60 and 3/171 (1.8%) having eGFR < 30. 47/171 (27.5%) circled 'no' to all risk markers. Percentage for sensitivity is 81.1% (95% confidence interval (CI) 64.8-92%), for specificity 29.9% (95% CI 22.3-38.4%), for positive predictive value 24.2% (95% CI 17-32.7%) and for negative predictive value 85.1% (95%CI 71.7-93.8%). Kidney disease, anaemia, myeloma and vasculitis seem to be statistically significant risk factors (P < 0.05). All three true-positive patients with eGFR < 30 indicated known kidney disease. Seven false-negative patients had eGFR 30-60, with 4/7 (57.1%) having CIN risk markers in their medical records.

CONCLUSION: Questionnaire screening for CIN risk has a high negative predictive value (85.1%) even in patients older than 60 years.