[Tamm-Horsfall protein, alpha-1- and beta-2-microglobulin as kidney function markers in heart surgery]

After cardiac surgery, transient renal dysfunction often occurs. Regional differentiation of these processes is possible only using invasive techniques, including renal biopsy. Approximately 30 different plasma protein components have been identified in the urine of healthy individuals by means of qualitative and quantitative immunochemical methods. The detection of microalbuminuria has high diagnostic relevance for the early diagnosis of renal damage at a reversible stage. One typical urinary protein is Tamm-Horsfall protein (THp). After histochemical staining of human kidney sections, activity is seen in the loop of Henle and initial distal tubule. The assay of alpha-1 microglobulin (MG) in urine is considered one of the most efficient laboratory parameters for the diagnosis of tubular lesions. Serum concentrations of alpha-1 MG are less dependent on extrarenal changes than are those of other low-molecular-weight proteins. beta-2 MG is also one of the standards used in recent years for diagnostic relevance. Urinary albumin excretion, normally less than 30 mg per day, sometimes increases after glomerular damage. Some renal function tests are used daily in many intensive care units, e.g. creatinine clearance (CCr) or urea and sodium excretion. Renal dysfunction should, however, be further examined to localise regional damage and to seek new clinical standards in addition to the conventional tests. METHODS. After obtaining the agreement of the local ethics committee, 30 patients were divided into two groups of 15 each: group I without renal dysfunction and CCr more than 60 ml/min; and group II with CCr below 60 ml/min. THp and alpha-1 MG were measured pre- and postoperatively after open heart surgery with the ELISA and beta-2 MG with the nephelometric technique. These parameters were compared with clinical standards such as albumin excretion, blood urea nitrogen (BUN), urea clearance, and fractional sodium excretion. RESULTS. The CCr did not change in group I from the pre- to postoperative period (81.5 to 85.1 and 91.4 ml/min), nor did excretion of THp (20.1 to 25.0 and 24.8 mg/day), correlation r = 0.7; P < 0.001). The elimination of alpha-1 and beta-2 MG was significantly higher in the postoperative period in this group (alpha-1: 7.2 to 44.1 and 100.6 mg/day; beta-2: 0.3 to 2.1 and 3.2 mg/day). In group II CCr showed pathological values (36.8 to 31.1 and 36.3 ml/min), as did simultaneous THp (13.5 to 9.7 and 12.7 mg/day). alpha-1 and beta-2 MG values became more pathological in the postoperative period than in group I (alpha-1: 32.8 to 113.9 and 198.5 mg/day; beta-2: 0.7 to 5.8 and 16.9 mg/day). DISCUSSION. Measurement of the excretion of THp and alpha-1 and beta-2 MG is a useful addition to present clinical standards for recognising early changes in renal function. The increases in the postoperative period after cardiac surgery showed tubular damage even in patients without predictive risk factors or clinical signs. In patients with renal dysfunction open heart surgery and extracorporeal circulation led to significant tubular damage.