On clarifying the requirement for DNA testing, the U.S. consulate in Mumbai has recently indicated:
DNA testing may be recommended to support an application for an immigrant visa or to transmit U.S. citizenship.
This means DNA testing is not always required. It is wise to clarify your situation with consulate or embassy before visiting.
The United States Government requires that you use an American Academy of Blood Bank approved lab. Labs are added and removed, so you'll need to go directly to their approved list. This list can be found at http://www.aabb.org/About_the_AABB/Stds_and_Accred/aboutptlabs.htm. Some labs confuse the INS guidelines with the Dept. of State guidelines and request a case number or even refuse to send the kit to you. Start preprations early.
You’ll have to coordinate the shipping arrangements (both ways) directly with the lab. You must have the kit sent to the consulate or embassy. If you are having the kit sent to the embassy, it is wise to notify them that you have done so, so they can look out for the package and confirm receipt. At the time of testing, you will need to provide a prepaid envelope for shipping the samples from Mumbai back to the lab for processing; the lab may include this for you - check with them. The consulate will be the ones to actually initiate the shipment, but requires a prepaid return envelope for this.
In Mumbai, The DNA test must be done at Bridge Candy Hospital next to the US embassy. Either on the day of your embassy appointment or during a separately scheduled DNA appointment (it's best to discuss your case with the consulate officers, as their recommendation on whether to do both these appointments on the same day or on separte days seems to change over time) you will meet with an Indian Physician at Bridge Candy Hospital. You need to go to a building across from the embassy, which is just a stones throw away from the hospital across the parking lot to the right of the hospital entrance. Here you will be asked to produce your baby’s birth certificate. You will then pay for the swabbing (350 Rupees per person) and they will hand you a slip for the test. When that process is complete you will be directed to the appropriate place in the hospital where the swab will be performed.
In an email, the consulate indicated:
Our current procedure is that the parent(s) and child appear together (at the same time) for a single appointment at a hospital near the consulate, where a cheek swab is taken for each person to be tested. That way, there is no doubt as to from whom the contributions were collected.
A US embassy official will also be present. They will require a few items from you at that time.
1. The Original Birth Certificate and one additional copy.
2. A Copy of your passport
3. A 2x2 Photo of self
4. The DNA Kit (keep the kit in the Fedex envelope if you were the recipient of the kit)
5. DNA testing fee
Once the DNA Swab is done, the embassy official will seal it and place it in the return prepaid Fed Ex envelope provided by your lab. They will be responsible for shipment and will arrange for Fed Ex to pick up the package. Do get the tracking number so you can track the package. Once the DNA results are on their way back to the Embassy you can call them to let them know. They will notify the mailroom to expect your results.
Since this is often the most time consuming step, once the embassy receives the DNA test results, they'll contact you to come to the embassy to pick up the passport.
These procedures are all subject to change, so do contact the embassy or consulate to get an update on the most current procedures.