Final answer:
Positive pressure in the intercapillary lumen during dengue fever is a symptom and refers to increased fluid pressure within the capillaries, associated with complications such as dengue hemorrhagic fever and dengue shock syndrome. Serologic testing, such as ELISA and RT-PCR, are used for the diagnosis of dengue fever.
Step-by-step explanation:
The correct answer to the question is b. A symptom of dengue fever. The term 'positive pressure intercapillary lumen' in relation to dengue fever refers to the state where there is an increased pressure exerted by the fluid within the capillary space. This symptom is indicative of the increased vascular permeability that can occur during dengue infection, which could lead to dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS) in severe cases. Diagnostic tests for dengue fever include serological testing, such as ELISA and reverse transcriptase-polymerase chain reaction (RT-PCR) of blood samples.
Venoconstriction, mentioned in a separate context, increases blood pressure within the vein, blood flow within the vein, and the return of blood to the heart. Yet, it should be noted that this is not directly related to the symptoms or diagnostic approaches for dengue fever.