How can you tell the difference between a blood clot and a muscle strain when you have mild calf pain?

Calf pain: Strain is usually caused my a history of trauma. Very localized tenderness and swelling.Blood clots in the calf typically present with widespread swelling ,tenderness, increase in pain with squeezing the whole calf but can only be diagnosed by testing. Currently tested by a Doppler study. Many times the calf pain produced by a clot increases with time.