What is the role of blood tests in the evaluation of hypertensive disorders during pregnancy?

Updated: Jun 12, 2018
  • Author: Michael P Carson, MD; Chief Editor: Edward H Springel, MD, FACOG  more...
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Include a CBC count. In cases in which an incidental platelet count is less than 150,000/µL, 75% are secondary to dilutional thrombocytopenia of pregnancy, 24% are due to preeclampsia, and about 1% of cases are due to other platelet disorders not related to pregnancy. Counts less than 100,000/µL suggest preeclampsia or immune thrombocytopenic purpura (ITP). Examination of the peripheral blood smear for evidence of microangiopathic hemolysis and thrombocytopenia may reveal the presence of red blood cell (RBC) fragments. In this setting, the diagnoses of hemolytic-uremic syndrome (HUS), thrombotic thrombocytopenic purpura (TTP), and HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet [count]) should also be considered.

Hemoglobin levels greater than 13 g/dL suggest the presence of hemoconcentration. Low levels may be due to microangiopathic hemolysis or iron deficiency. Prothrombin time (PT) and/or international normalized ratio (INR) and/or activated partial prothrombin time (aPTT) results may be abnormal in consumptive coagulopathy and disseminated intravascular coagulopathy (DIC) complicating severe preeclampsia. However, checking the PT/INR/aPTT is not necessary in the absence of abnormal liver transaminases or thrombocytopenia.

Abnormal values of lactate dehydrogenase (LDH), bilirubin, haptoglobin, fibrinogen, and D-dimers may confirm the presence of hemolysis and DIC, along with coagulation testing. It is unnecessary to check levels of LDH, bilirubin, haptoglobin, fibrinogen, and D-dimers, unless the PT/INR/aPTT results are abnormal, thrombocytopenia is present, or the hemoglobin level is dropping.

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