Laboratory Studies
Once purpura fulminans is suspected, workup should begin immediately to identify the underlying etiology. Laboratory studies are the primary diagnostic tools for working up purpura fulminans and should include the following:
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Complete blood count (CBC) with differential
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Basic metabolic panel
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Liver function tests
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Prothrombin time, international normalized ratio, and activated partial thromboplastin time
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Fibrinogen, D-dimer levels
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Blood cultures
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Qualitative/quantitative coagulation cascade protein assays
Abnormalities in the CBC and coagulation cascade indicate DIC, as highlighted in the table below.
Table 1. (Open Table in a new window)
Typical Lab Values in Acute Disseminated Intravascular Coagulation (DIC)* |
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Lab Test |
Acute DIC |
Reference Range |
Platelet count |
< 150,000/L |
150,000-450,000/L |
Fibrinogen |
>340 mg/dL |
170-340 mg/dL |
Prothrombin time (PT) |
>13 seconds |
9-13 seconds |
Activated partial thromboplastin time (aPTT) |
>35 seconds |
23-35 seconds |
D-dimer |
>250 ng/mL |
0-250 ng/mL |
*Table created using data from: Levi M, Toh CH, Thachil J, Watson HG. Guidelines for the diagnosis and management of disseminated intravascular coagulation. British Committee for Standards in Haematology. Br J Haematol. 2009 Apr;145(1):24-33.
Histologic Findings
A peripheral blood smear may indicate microangiopathic hemolytic anemia (MAHA) with schistocytes, bite cells, and helmet cells. (See the image below.)
Schistocytes (arrows) on a peripheral smear. Courtesy of Bodhit AN, Stead LG. Altered mental status and a not-so-benign rash. Case Rep Emerg Med. 2011;2011:684572.
A study by Brozyna et al indicated that even in culture-negative cases, acute infectious purpura fulminans can be identified based on its histopathology. The 11 patients in the study were diagnosed with signs of acute infectious purpura fulminans, including sepsis and, histopathologically, intravascular thrombosis and/or DIC. These findings correlated with lesions identified on clinical examination. Focal epidermal ischemia or necrosis was found in most of the 13 skin biopsies, with full-thickness epidermal necrosis demonstrated in three of them. The underlying dermis was seen to feature “fibrin thrombi in superficial and deep blood vessels with acute inflammation,” while five cases revealed changes related to an inflammatory, destructive vasculitis. Bacteria and fungi, however, did not show up on histopathologic examination. [20]
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Lesion associated with purpura fulminans in an adult patient. Courtesy of DermNet New Zealand.
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Schistocytes (arrows) on a peripheral smear. Courtesy of Bodhit AN, Stead LG. Altered mental status and a not-so-benign rash. Case Rep Emerg Med. 2011;2011:684572.
Tables
Typical Lab Values in Acute Disseminated Intravascular Coagulation (DIC)* |
||
Lab Test |
Acute DIC |
Reference Range |
Platelet count |
< 150,000/L |
150,000-450,000/L |
Fibrinogen |
>340 mg/dL |
170-340 mg/dL |
Prothrombin time (PT) |
>13 seconds |
9-13 seconds |
Activated partial thromboplastin time (aPTT) |
>35 seconds |
23-35 seconds |
D-dimer |
>250 ng/mL |
0-250 ng/mL |
