Can blood tests tell if you have a blood clot?

D-dimer: Depending on the cutoff level, this point-of-care test can help rule out a dangerous blood clot such as one in the leg or lung.

Yes but not where: D-dimer is a blood test that is very sensitive to tell you if you have blood clot or not but does not tell you where is the clot. So even minor trauma or cut can cause elevation but in normal person if d-dimer is normal this can rule out clot.

Not really: There is a test called d dimer that, if negative, makes having a blood clot very unlikely. However a positive test may not mean much. The test provides many false positives. If concerned, a painless ultrasound is the best way to make the diagnosis.