confused

[Leane]

  After trying to conceive last month, my period is now almost 2 weeks late.
  (It was due on 4/29) After several negative HPTs, I decided to have
  a blood test done by my doctor, which also came back negative.  She suggested I home test again in a week or two.  But blood tests are conclusive, right?????? Why is my period so late, and why should I test again if a blood test came back negative????  I am very frustrated and confused......

[hfhs.md.db]

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Blood and urine pregnancy tests measure the same thing, hCG. Blood tests will become positive earlier (several days to a week) than urine tests, but once the hCG level in the blood reaches approximately 50 mIU/ml, the urine test will become positive.
If your cycles are somewhat irregular or occasionally run long, then it is possible that you are pregnant and that the first test simply was done too early to be positive (blood tests become positive 5-7 days after conception).
More likely is that you are not pregnant and are having a delayed menses. Although this can be caused by functional ovarian cysts, usually no specific cause is identified for a late period. Although an ultrasound is useful, for the average weight patient a physical exam will detect functional cysts of significant size.
My suggestion would be to wait 1-2 weeks and have a repeat blood hCG and physical examination. If these are both negative then the options are to do nothing and wait for an eventual menses or to bring on a period (and "reset" the cycle) with a short course of Provera. Both options are essentially equivalent but the induced menses will allow you to start attempting pregnancy sooner (if this is what you desire).