[alpha 2-macroglobulin in urine. Significance for differential diagnosis of rejection and infections after kidney transplantation].

: The value of measuring the urinary concentration of alpha 2-macroglobulin in addition to that of C-reactive protein (CRP) was assessed in a prospective study of 78 consecutive patients (29 women, 49 men; mean age 48.7 [19-75] years) after renal transplantation. alpha 2-Macroglobulin was never demonstrated in urine when the course was normal (n = 38), cytomegalovirus infection had occurred (n = 26) or acute cyclosporin nephrotoxicity (n = 5) or glomerular disease in the transplant (n = 10). CRP was present in only a few such cases. Interstitial rejections (n = 26) always led to urinary alpha 2-macroglobulin and CRP excretion without haematuria, while in vascular rejection (n = 3) the haemoglobin test was also positive. Urinary infection (n = 20) and urosepticaemia (n = 6) always brought about the urinary excretion of alpha 2-macroglobulin and CRP, as well as a usually highly positive haemoglobin test. alpha 2-Macroglobulin was absent but CRP always present in extrarenal bacterial infections (n = 30). Postrenal blood admixture was always characterized by a positive haemoglobin test and alpha 2-macroglobulin in urine, while in most cases (83%) CRP was absent. --These results indicate that the constellation "alpha 2-macroglobulin negative/CRP positive" is a pathognomonic for extrarenal bacterial infection (sensitivity 100%, specificity 98.9%). The presence of alpha 2-macroglobulin alone makes postrenal blood admixture probable. If both proteins are present in the urine, rejection and urogenital bacterial infection must be excluded by further tests.