Can clearblue dig. test be wrong if ur periods are irregular but u take it on the 30th day my periods have been up to 40 days apart?

HPT not =100%: Although the hpts are quite good and many claim over 99% accuracy, which means less than 1% false. So, it is possible to have a pregnancy and the test is not picking it up, but low chance. More often than not is that it is too early for the test to pick-up (less than 14 days since conception). Repeat in few days or have a blood test will confirm your suspicion. Consult doc. Good luc.