I also had 'high' levels (194) at 10 weeks. We did our first repeat 24 hour when other symptoms were present, like worsening BP.
Like the previous poster said, our doctors mentioned that because we were already spilling we probably had an underlying condition causing it, or had done damage to our kidneys in our last pregnancy.
Our MFM also told us that because we were higher to start, that although 300 was diagnostic, they wouldn't really be as concerned until it was "significantly" higher, which he also said was very subjective since "significantly" higher isn't a number and can change depending on provider.
2008-Our Baby Girl, PTL born too early at 30w6d, Fought so hard... Forever Loved & Missed
2010- Lil' Bro, Pre-E at 29 weeks... Induced at 36w6d, Born 37w
2012- Lil' Sis, Super-imposed pre-e at 25 weeks, PTL & GD at 35 weeks, Evicted 36w