WORCESTER, MASS--Measurement of both D-dimer and fibrinogen/fibrin degradation products (FDP) appears to be the best method currently available for diagnosing disseminated intravascular coagulation (DIC). In a recent retrospective study of 82 critically ill patients, this combination was 91% sensitive and 94% specific for DIC.[1]

"Physicians order an indiscriminate number of tests when they suspect DIC," Liberto Pechet, MD, one of the study authors, recently told Pulmonary Reviews. "This approach is costly and nonspecific." Among the battery of tests commonly used to diagnose DIC are thrombin time (TT), prothrombin time (PT), partial thromboplastin time (PTT), and antithrombin (AT) assays. Dr. Pechet and colleagues found that although these tests had high sensitivity for DIC, their specificity was low.

SEARCHING FOR SUBJECTS

To identify study subjects, the authors searched their laboratory's computer system for patients in the intensive care unit (ICU) who had undergone fibrinogen or FDP tests during a three-month period. Those assays are "the two tests most commonly used by our staff to diagnose DIC," the investigators explained. Patients who presented with isolated thrombosis were excluded from the study. Subjects with potentially chronic DIC were excluded as well, because of the study's focus on ICU patients.

Because no independent diagnostic criterion for DIC exists that is both practical and reliable, the authors devised a scoring system incorporating clinical presentation and diagnostic tests. The score assigned one point for each of the following: DIC-related diseases or injuries (eg, septicemia, leukemia, or crush injuries); thrombohemorrhagic events (eg, petechiae, purpura, or wound bleeding); elevated PT, PTT, or TT; thrombocytopenia; decreased fibrinogen; elevated FDP; elevated D-dimer; and low AT. A score of at least five was required for diagnosis of DIC.

HOW THE TESTS PERFORMED

The diagnosis was confirmed in 31 (37.8%) of the 82 patients in whom the disorder was suspected. These 31 patients accounted for 7.8% of all ICU patients during the three-month study.

The combination of FDP and D-dimer testing was by far the best diagnostic method. Not only did this combination have high sensitivity and specificity, but its efficiency (defined as whether the test result, positive or negative, correctly classified the presence or absence of DIC) was 95%. The second best test for DIC diagnosis was the FDP assay alone; it had 100% sensitivity, 67% specificity, and 87% efficiency. After that came the FDP-PT-PTT combination and the D-dimer test alone. Both methods had 91% sensitivity, about 70% specificity, and at least 80% efficiency.

By itself, the fibrinogen measurement was 100% specific but only 22% sensitive and 65% efficient. In contrast, five other tests (PT, PTT, TT, AT assay, and platelet count) had high sensitivity but low specificity and efficiency. The presence of schistocytes had only 23% sensitivity, 73% specificity, and 51% efficiency for diagnosing DIC.

The authors concluded that the combination of FDP and D-dimer testing is the best method for DIC diagnosis in most settings. However, Dr. Pechet, Director of the Hematology Laboratory at the University of Massachusetts Memorial Health Care in Worcester, added that fibrinogen testing may be preferable in obstetric patients; such patients were not included in this study.

In addition, Dr. Pechet noted that "the AT assay is also useful, but not as a diagnostic test." Because AT levels reflect DIC severity, he explained, this measurement may help in forming a prognosis. It may also help to monitor AT replacement, an emerging therapy for DIC patients with decreased AT levels.

--Timothy Begany

Reference
1. Yu M, Nardella A, Pechet L. Screening tests of disseminated intravascular coagulation: guidelines for rapid and specific laboratory diagnosis. Crit Care Med. 2000;28:1777-1780.

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