Thrombotic microangiopathy - Diagnosis

Laboratory diagnostics of thrombotic microangiopathy

Diagnosis of thrombotic microangiopathy consists of identifying the main markers of this disease - hemolytic anemia and thrombocytopenia.

Anemia develops within 1 to 3 weeks from the onset of the disease, is significantly expressed in most patients and requires blood transfusions in 75% of cases. In patients with hemolytic uremic syndrome, the average hemoglobin level is 70-90 g / l, although it can quickly decrease 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, and a decrease in blood haptoglobin indicate the presence of hemolysis. The most sensitive marker of hemolysis, directly correlating with its severity, is an increase in the level of LDH. However, in thrombotic microangiopathy, an increase in LDH activity is due not only to the release of the enzyme from erythrocytes, but also to ischemic damage to organs. The microangiopathic nature of hemolysis in HUS/TTP is confirmed by a negative Coombs reaction and the detection of deformed, altered erythrocytes (schistocytes) in a peripheral blood smear.

Thrombocytopenia is more pronounced in thrombotic thrombocytopenic purpura than in hemolytic uremic syndrome. At the onset of thrombotic thrombocytopenic purpura, the platelet count often decreases to 20,000 in 1 μl, while in hemolytic uremic syndrome it usually decreases to 30,000-100,000 in 1 μl, although a normal platelet count 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. A study of platelet function reveals impaired adhesion and aggregation in vitro, a decrease in their lifespan, and signs of activation in vivo: increased levels of platelet factor 4, beta-thromboglobulin, and serotonin in plasma. Platelet dysfunction may persist even after their count has returned to normal.

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

In HUS/TTP, changes in the blood coagulation system are detected - an increase in fibrin degradation products, an increase in thrombin time. The concentration of fibrinogen is only slightly reduced at the onset of the disease (which indicates a lower consumption of it in thrombus formation processes compared to platelets), and then normalizes and even increases. Activated partial thromboplastin time and prothrombin time remain within normal limits, confirming the rarity of the development of DIC - a syndrome in thrombotic microangiopathy.

Differential diagnosis of thrombotic microangiopathy

Kidney biopsy is not indicated for children with postdiarrheal hemolytic-uremic syndrome to clarify the diagnosis of thrombotic microangiopathy due to the typical clinical picture and the possibility of complete recovery. In thrombotic thrombocytopenic purpura and atypical forms of hemolytic-uremic syndrome, morphological examination of kidney tissue is necessary to verify 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 from each other. In addition, thrombotic microangiopathy should be differentiated from rapidly progressive glomerulonephritis, sepsis with multiple organ failure, malignant arterial hypertension, systemic lupus erythematosus, acute scleroderma nephropathy, catastrophic antiphospholipid syndrome.

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