Hello, I can understand your concern very well. I would like to tell you that all the pregnancy test strip works on same principle, so you can use the strip of any of the manufacturing company. Coming to your confusion regarding in vitro use only , i would like to tell you that all the pregnancy test strips should be used in vitro only. In vitro means outside your body, so you need to put a drop of urine (possibly early morning urine after voiding few drops) on the strip and after 5 to 10 minutes you will see the lines, so you can interpret whether its positive or negative. This test usually becomes positive after 30 to 35 days of your last period, but in some cases (low HCG levels) it might be very faint positive or false negative, so in that case you can repeat the test after a week or go for ultrasound to confirm the pregnancy. Hope this answers your question and let me know directly if you are having any follow up queries.