Paul Kim
Analyst · Piper Jaffray
Thanks, Ming. Revenue for the first quarter was $5.3 million, an increase of 54% over the first quarter of 2016. As Ming mentioned, we continue to see strong growth in our billable test volume, our revenue declined from Q4 2016, due to an increase mix of lower priced tests. Billable tests were 4,422 in the quarter, an increase of 82% year-over-year and 14% from Q4 2015.
Our average selling price was approximately $1,200, down meaningfully from last quarter due to our product mix. Cost per test for the quarter was $420 on a GAAP basis and $387, excluding equity-based compensation of $146,000, representing an 11% decrease from Q4 2016 on a non-GAAP basis.
Despite the ASP and revenue decline from last quarter, as Ming mentioned, our non-GAAP gross margin remained consistent at 68% for the quarter. We expect our gross margin may fluctuate as our test mix varies quarter-to-quarter. However, we expect to focus on continuing to drive down cost per test via increased volumes and continued automation and productivity in the lab, which will continue to counter any pricing degradation we may see in our business or in the industry generally.
Moving to operating expenses. We made meaningful investments in the quarter with the hiring of senior members to our sales team, which Ming discussed. We added 6 individuals to our sales and marketing team and anticipate having approximately 13 sales employees at the end of our second quarter. Though the changes may not impact our top line numbers in the coming few months, we anticipate the restructuring and reinforcing of the sales organization will be highly beneficial for the company longer term.
On research and development, we remain focused on advancing our technology platform and we'll continue to efficiently invest in research and development. Lastly, we saw greater than expected administrative expenses of legal and accounting expenses from the annual audit exceeded our initial estimates.
With the hiring across all departments, combined with our joint venture's operational lab in China, we now have increased capacity to handle any spike in volume. We also believe we can continue to decrease our cost per test as we increase our operating efficiencies.
Adjusted EBITDA for the first quarter was $1.2 million compared to $2.2 million last quarter and $1.2 million last year. On a non-GAAP basis and excluding equity base compensation expense, non-GAAP income for the quarter was $560,000 or $0.03 per share based on 18.2 million shares outstanding. The GAAP tax rate at the end of the first quarter was 31% and non-GAAP tax rate was 38%.
In sum, although we're not pleased with lower than anticipated revenue, we posted another quarter of GAAP income and positive cash flow, and we believe we're well positioned to continue scaling our business in the future.
Turning to the balance sheet, we remain well capitalized to support growth and expansion plans. We finished the first quarter with $47 million in cash, cash equivalents and marketable securities with no debt.
Now, I will move to our outlook for the next quarter and the balance of the year. The biggest factor we have taken into consideration in providing our outlook is the time needed for our new sales organization to have an impact on revenue generation. Though we do not expect it would take much time for these senior individuals to get up to speed, it will take a few months for them to develop familiarity with our products, tests, pricing, lab process and systems. Also there'll be a lag between obtaining any new customers and recording revenue from those customers.
Also, although we have been talking about uncertainty regarding product mix and pricing for some time, we did not anticipate a 20% drop in ASPs in one given quarter. Based on these factors, we anticipate second quarter revenues will be slightly lower than Q1 revenue. We also anticipate our revenue for the full year will be lower than our initial guidance. We now expect the revenue for the full year 2017 to be in the range of $24 million to $28 million.
Given the dynamic nature of our new sales organization, we plan on providing greater color into our business in the coming earnings calls, including order volumes and traction from new cash paying customers. Also, should product mix shift into our favor and we sell a greater portion of exome-based test, this dynamic would provide upside our guidance. Regardless of product mix or timing on how quickly the reinforced sales force can produce results, we expect we will maintain our strong gross margin as well as GAAP income for the year due to our technological and operational efficiency, even as we continue to make aggressive investments in our business.
Despite our lower outlook for the year, we remain confident in our business and opportunities ahead. We expect that the changes we have made to our sales organization will pay dividend in the long term and we are optimistic about what can be accomplished with the differentiated technology and platform in a rapidly growing market. We have a solid balance sheet and remain one of the few companies in the genetic testing space able to demonstrate GAAP profits while still investing for growth.
Operator, now we'll open it up for questions.