Serum amyloid A protein: a sensitive indicator of renal allograft rejection in humans

Acute human renal allograft rejection induces a dramatic elevation of serum amyloid A protein (SAA). To evaluate the clinical significance of this finding we monitored 31 consecutive recipients of cadaveric renal allografts by daily SAA measurements. SAA increased significantly during 37/38 rejection episodes. Mean peak SAA level during the reversible rejections was 271 +/- 31 mg/L (SE, median 220 mg/L, n = 35) and during the irreversible rejections 680 +/- 29 mg/L (median 705 mg/L, n = 3). Excluding the predictable operation-induced SAA elevations that peaked on the second post-operative day, there were seven out of 42 SAA elevations (greater than or equal to 100 mg/L) not due to rejection. They were all caused by severe infections, and in one instance by a surgical complication. In 17 of the 35 SAA-positive rejections the SAA elevation (greater than or equal to 100 mg/L) preceded the clinical diagnosis by 1-5 days; in 11 it occurred on the same day; and in 7 one day later. Rejection episodes in recipients with initially nonfunctioning grafts were all also characterized by significant SAA elevations. We conclude that daily monitoring of SAA concentrations offers a valuable aid in the early diagnosis of acute allograft rejection. The SAA test is not a renal function test, so it can also be carried out in transplant patients who are anuric or oliguric in the postgrafting stage.