I am pretty sure I am not pregnant and using the same brand tests that have produced lines before with blood on hpt , did one normal and one double dye. NOTHING. Also, when mine were producing lines before we tested my friend who was trying but was not pregnant, and also a male who volunteered, with no lines coming up for them.
So personally I think there is smth in it.
The very first time I got a line on a hpt was on frer at 10dpo, and still got a bfn with urine until late evening of 12dpo, that was with my youngest son.