A quote from NY Times:
For the first quarter, the bureau now says G.D.P. grew at a 1.1 percent rate — after a series of reductions from its initial estimate of 2.5 percent.
Why is there no article before GDP? It is an initialism, spelled out letter-by-letter, and I've read that they are generally used with THE. What's more, the reader knows from the text that the country in question is the US, so that's a specific and definite GDP, not some GDP in general.