Thrombotic microangiopathy: diagnosis

Laboratory diagnosis of thrombotic microangiopathy

Diagnosis of thrombotic microangiopathy is to identify the main markers of this disease - hemolytic anemia and thrombocytopenia.

Anemia develops in the period from 1 to 3 weeks from the onset of the disease, in most patients it is significantly expressed and in 75% of cases it requires blood transfusions. In patients with hemolytic uremic syndrome, the average hemoglobin level is 70-90 g / l, although it is possible to rapidly reduce it to 30 g / l. The severity of anemia does not correlate with the degree of acute renal failure. High reticulocytosis, an increase in the level of unconjugated bilirubin, a decrease in the haptoglobin of the blood indicate the presence of hemolysis. The most sensitive marker of hemolysis, directly correlated with its severity, is an increase in LDH levels. However, with thrombotic microangiopathy, the increase in LDH activity is due not only to the release of the enzyme from erythrocytes, but also to ischemic organ damage. The microangiopathic nature of hemolysis in HUS / TTP is confirmed by the negative reaction of Coombs and the detection of deformed, altered erythrocytes (schizocytes) in the peripheral blood smear.

Thrombocytopenia is more pronounced in thrombotic thrombocytopenic purpura than in hemolytic-uremic syndrome. In the onset of thrombotic thrombocytopenic purpura, the platelet count is often reduced to 20,000 in 1 μl, with hemolytic-uremic syndrome - usually up to 30,000-100,000 in 1 μl, although a normal number of platelets in the blood is possible. Thrombocytopenia persists for 7-20 days, but its severity and duration do not correlate with the severity of the disease. The study of platelet function reveals violations of adhesion and aggregation in vitro, a decrease in their lifespan, as well as signs of in vivo activation: an increase in plasma levels of the 4 th platelet factor, beta-thromboglobulin, serotonin. Platelet dysfunction can persist even after the normalization of their number.

In patients with a typical hemolytic-uremic syndrome, leukocytosis is observed with a shift of the formula to the left, the severity of which is a prognostically unfavorable factor.

At HUS / TTP reveal changes in the coagulation system of blood - increase in products of degradation of fibrin, lengthening of thrombin time. The concentration of fibrinogen is only slightly reduced in the onset of the disease (which indicates a lower consumption of thrombocytes compared to platelets), and then normalizes and even increases. The activated partial thromboplastin time and prothrombin time remain within normal limits, confirming the rarity of the development of DIC syndrome in thrombotic microangiopathy.

Differential diagnosis of thrombotic microangiopathy

Patients with postdiadary hemolytic-uremic syndrome to clarify the diagnosis of thrombotic microangiopathy kidney biopsy is not indicated in connection with the typical clinical picture and the possibility of full recovery. With thrombotic thrombocytopenic purpura and atypical forms of hemolytic-uremic syndrome, morphological examination of the kidney tissue is necessary for verifying the diagnosis and differential diagnosis with other nephropathies occurring with progressive deterioration of kidney function. Hemolytic-uremic syndrome and thrombotic thrombocytopenic purpura must be differentiated with each other. In addition, thrombotic microangiopathy should be differentiated with rapidly progressive glomerulonephritis, sepsis with multiple organ failure, malignant arterial hypertension, systemic lupus erythematosus, acute scleroderma nephropathy, catastrophic antiphospholipid syndrome.

[1], [2], [3], [4], [5], [6], [7]