Coagulation Testing in Hypertensive Disorders of Pregnancy
Abstract & Commentary
To determine which routinely ordered laboratory tests could best predict abnormalities in prothrombin time (PT), activated partial thromboplastin time (aPTT), and fibrinogen, Barron and colleagues performed a retrospective pilot study of 73 women being evaluated for hypertensive disorders in pregnancy. They found that the platelet count and lactate dehydrogenase (LDH) best predicted coagulation abnormalities. These findings were then applied to a retrospective review of 732 women being evaluated for hypertensive disorders in pregnancy. About 30% of the larger group had coagulation tests obtained. An abnormal platelet count was defined as less than 150 × 109/L, an abnormal PT as a result exceeding the upper limit of normal or greater than 18 seconds, and an abnormal aPTT as exceeding the upper limit of normal or more than 40 seconds. Fibrinogen was considered abnormal if it was below 250 mg/dL. The overall likelihood of a coagulation abnormality was low in this population, no patient had a PT greater than 18 seconds, two had an aPTT greater than 40 seconds, and three had a fibrinogen below 200 mg/dL. All patients with a normal platelet count and a normal LDH had a normal PT and aPTT, and 99% had normal fibrinogen levels.
An abnormal platelet count or an elevated LDH had a sensitivity of 70% for the detection of an abnormal PT or aPTT and 79% for a fibrinogen below 250 mg/dL. There was no relationship between the results of the PT, aPTT, or fibrinogen in eight patients requiring transfusion of coagulation factors. Only the platelet count was correlated with this outcome.
Barron et al conclude that a PT, aPTT, or fibrinogen need not be ordered in patients suspected of having preeclampsia when there is no evidence of bleeding, or a condition that might produce a coagulopathy such as placental abruption, and the platelet count and LDH level are normal. (Barron WM, et al. Obstet Gynecol 1999;94:364-370).
Comment by Steven G. Gabbe, MD
On many obstetric units, when a patient with suspected pregnancy-induced hypertension or preeclampsia is admitted, a battery of laboratory tests is ordered including a complete blood count, platelet count, urinalysis, creatinine, uric acid, hepatic transaminases, LDH, and albumin. In some institutions, coagulation tests are obtained as well including a PT, aPTT, and fibrinogen. The coagulation tests are not only expensive but are usually requested as a "rush," further stressing the laboratory. This retrospective study by Barron et al demonstrates that, when the platelet count and LDH are normal, the coagulation tests will rarely be abnormal.
Although not evaluated in this study, Barron et al point out that other coagulation studies such as fibrin-fibrinogen degradation products, D-dimer, and anti-thrombin III should not be ordered routinely. An unpublished research project I completed with Bruce Farringer, MD and Patricia Temple, MD. revealed similar findings. Unless the patient with preeclampsia had thrombocytopenia or right upper quadrant pain, coagulation abnormalities or abnormalities in liver function tests were unusual. This information should be helpful in reducing unnecessary lab studies in patients with hypertensive disorders in pregnancy.
Based on the data of Barron et al, which of the following laboratory tests is not needed when the patient with pregnancy-induced hypertension is found to have a normal platelet count and a normal LDH value?
a. fibrinogen
b. creatinine
c. complete blood count
d. urinalysis
e. albumin
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