The most common cause of bruises is minor capillary break. There is no specific cause for it, is a self resolving phenomenon and is not worrisome. This is termed as Ecchymoses (bruise). This usually develop with or without noticeable trauma and do not spread into deeper tissues. This can occur due to the structural abnormalities of the small blood vessels called as capillaries, which break even with the slightest of the injury. This can occur due to the scurvy (vitamin C deficiency), steroid-induced purpura, small vessel vasculitis, and purpura associated with the presence of paraproteins. Aspirin or other pain medications may also be responsible which can increase the bleeding time. The diagnosis is based on the investigations. Though, with the possible exception of a prolonged bleeding time, screening tests are usually normal in patients with bleeding disorders related to vascular abnormalities (ecchymoses / bruising). Investigations are only advised, if this occur recurrently / frequently. Taking Vitamin C or eating citrus fruits or fresh juices may help.
The investigations done are;
1) platelet count,
2) bleeding time (BT),
3) prothrombin time (PT),
4) activated partial thromboplastin time (aPTT),
5) thrombin time (TT)
6) peripheral blood smear,
7) platelet aggregation in response to ADP, epinephrine, collagen, and ristocetin;
8) platelet release assays,
9) coagulation factor assays,
10) assessment of factor XIII activity via clot solubility testing
11) Tests of fibrinolysis; measurement of fibrin split products and D-dimer levels.
Your PCP can get them done. An initial screening can be done by the first 5 or 6 tests which would give very definitive clue to the diagnosis, but as we discussed are done when phenomenon is frequent.
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.