Since blood and daily urine excretion of creatinine shows minimal fluctuation, creatinine excretion is useful in determining whether 24-hour urine specimens for other analytes (e.g., protein) have been completely and accurately collected. To view specimen requirements and codes please Select a regional laboratory.
Ultrasound is almost foolproof at diagnosing twins, but the greater the number of babies, the less accurate the ability to detect how many there are. It's possible to see twins (or more) on a scan at around six weeks, though one baby may be missed at this early stage. Sometimes a heartbeat is seen in one sac, but not in the other. Rescanning in a week or two may reveal a second heartbeat, or the scan may show that one sac is growing and the other still empty.
And as far as a test goes, I did test positive at 11dpo, but I don't know if having twins had anything to go with it. I found out by u/s at 6 weeks. I think 5-6 weeks is the earliest you can really know by u/s. As far as other ways, my hCG didn't really lead me to believe twins. It was 77 at 12dpo, then 1489 one week later... so pretty on par with doubling every 48 hours.