Coagulation is important in two groups of renal disorders in man. In one group, the kidney is the major site of disease, and localized thrombosis and fibrin formation is superimposed on demonstrable immunological and or endothelial damage. These disorders will not be discussed here. In the second group, renal lesions associated with fibrin formation are involved as a consequence of systemic intravascular coagulation or DIC [
99]. In the latter group, acute renal failure (ARF) is the usual associated renal presentation, occurring in the course of sepsis, major surgery, severe trauma, and hypovolemic and cardiogenic shock. The pathogenesis of ARF in these conditions is caused by hypoperfusion resulting in ischemia–reperfusion injury. The decrease in oxygen saturation and hormonal dysregulation causes acute tubular necrosis [
100]. At least in septic shock, it has been suggested that microthrombi contribute to ARF [
101,
102]. The older literature strongly suggests that intravascular coagulation causes immediate changes that are detrimental to renal function. Electron microscopical studies have shown that coagulation causes mesangial swelling and an increase in vacuoles, organelles free ribosomes, and mitochondria [
103]. These changes were associated with phagocytosis of fibrin and secretion of basement membrane-like material. The glomerular lesions occurring in the course of DIC may resemble those seen in acute glomerulonephritis, with platelets and fibrin deposits intraluminally, swollen endothelium, subendothelial deposits of fibrin cleavage fragments, and cellular proliferative effects. When these processes continue, complete occlusion of glomerular capillaries and hyalinization of glomeruli may follow [
99]. The pathophysiology of renal failure in shock is also thought to be influenced by vasoactive substances, and renal damage was markedly reduced by adrenergic blockade in a model of hemorrhagic shock or endotoxin shock [
104]. Catecholamine infusion in experimental animals causes shock and DIC. Heparin reduces the effects of catecholamine-induced shock and endotoxin-related complications in animal models. It thus appears that the combination of hypoperfusion-related ischemia–reperfusion injury and vasoactive reactions are of major influence on the occurrence of ARF in shock. The finding of fibrin deposits suggests that DIC contributes to organ damage, and the observed improvement under heparin treatment supports this concept. The trigger to thrombosis is probably locally induced by the ischemia–reperfusion responses of hypoxia-inducible factor-mediated TF expression [
105]. In addition, systemic stimuli such as endotoxin cause cytokine-mediated upregulation of TFmRNA in the kidney, while local fibrinolytic defense mechanisms are also activated (u-PA and t-PA, without concurrent upregulation of PAI-1). Furthermore, experimental studies have demonstrated that specific blockade of the factor VII–TF complex reduced fibrin in the kidney [
106]. Infusion of hirudin caused a dose-dependent decrease in mortality and also reduced the amount of fibrin deposition in the kidney. An important role of the protein C system in preventing glomerular thrombosis may be inferred from the abundant presence of thrombomodulin expression on endothelial cells in the glomerulus [
107]. In inflammatory glomerular disease, such as acute membranoproliferative or lupus glomerulonephritis, an increase in thrombomodulin expression has been implicated [
108]. In contrast, in ischemia–reperfusion injury in kidneys, thrombomodulin has been markedly downregulated. Administration of soluble thrombomodulin to rats with renal ischemia–reperfusion injury prevented massive glomerular thrombosis and kidney dysfunction [
109]. In another experimental study of renal ischemia and reperfusion, administration of activated protein C prevented histological changes and the decrease in renal blood flow, and preserved kidney function, whereas treatment with active site-blocked factor Xa, heparin, and inactivated protein C were less effective [
110]. It therefore appears that inhibition of coagulation also reduces the amount of fibrin in the kidney. This may imply an improvement of renal function; however, there have been no controlled trials in which the beneficial effect of anticoagulant treatment in patients with DIC and ARF was investigated.