Beta-2-microglobulin for differentiation between ciclosporin A nephrotoxicity and graft rejection in renal transplant recipients.

The clinical relevance of daily measurement of beta 2-microglobulin in serum and urine was evaluated in 49 patients undergoing renal transplantation. The changes in beta 2-microglobulin levels were compared to standard parameters for assessment of renal function. One hundred episodes of acute deterioration of renal function, clinically diagnosed as rejection, were analyzed retrospectively: (1) In 18 episodes renal malfunction did not respond to methylprednisone but improved immediately upon dose reduction of ciclosporin A, thus indicating a nephrotoxic effect of the drug. In these cases a mean increase of beta 2-microglobulin in urine as high as 7.9 mg/l was observed while serum values decreased. (2) Fifty episodes of apparent rejection (responsive to steroids) were preceded by a 3-day lasting continuous rise of beta 2-microglobulin in serum of up to 3.6 mg/l as a mean with only a moderate elevation in urine. (3) In 13 episodes antirejection treatment could have been avoided as continuously declining laboratory parameters indicated spontaneous improvement of renal function. We conclude that parallel determination of beta 2-microglobulin in serum and urine allows to differentiate between ciclosporin A nephrotoxicity and rejection in 91% of the cases.