Probability of rejection predicted from ultrasonographic measurement of renal transplant swelling

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Abstract
Serial ultrasonographic measurements of renal transplant crosssectional area were used to quantify allograft swelling as a diagnostic test of acute rejection. Eighty consecutive episodes of acute allograft dysfunction (rise in creatinine level ⩾ 10 per cent or ⩾ 30 μmol l−1) were investigated. Needle core biopsy was performed in all cases to diagnose acute rejection. Rejecting transplants demonstrated a median (interquartile range) swelling of 16·2 (12·1–25·5) per cent compared with 2·2 (−2·0 to 8·4) per cent for non‐rejecting organs (P < 0·001). A ⩾ 10 per cent increase as the diagnostic threshold for rejection yielded a sensitivity of 80 per cent, specificity of 77 per cent, positive predictive value of 85 per cent, negative predictive value of 71 per cent and overall accuracy of 79 per cent. Using a logistic regression model, predictive probabilities of rejection for individual changes in cross‐sectional area were calculated. A 20 per cent increase was associated with a predicted probability of rejection of 87 per cent (95 per cent confidence interval 75–94 per cent). There was a significant correlation between the functional severity of rejection and the degree of transplant swelling (rs = 0·63, P < 0·001). Ultrasonographic measurement of renal transplant cross‐sectional area is a simple non‐invasive test for the diagnosis of acute rejection.