Thanks, Ming. Revenue for the fourth quarter was $5.85 million, which is double last year's fourth quarter and a 17% increase over the third quarter of 2016. Our revenue growth was driven by increased penetration into our current customer base and market share gains in our core hospital market, both domestically and internationally. And though still a very small portion of revenues, we continue to make headlines to establishing a presence in the third-party payer market by signing on regional states and are continuing to negotiate agreements with additional territories as well as various national payers. We expect to make incremental progress with third-party payers throughout 2017.
We generated 53% of our revenue in the U.S. and Canada and 47% outside of North America in the quarter. Our strong revenue growth overall was driven by a significant increase in billable test volumes, which grew to approximately 3,900 tests in the quarter, a sequential increase of 13% over approximately 3,400 billable tests in the third quarter.
Our average selling price was a record $1,509, which was a slight uptick from last quarter. Cost per test continue to decrease and was $437 for the quarter, excluding stock-based compensation of $168,000. This resulted in a record high non-GAAP gross margin of 71% in the quarter, an increase of over 700 basis points versus the fourth quarter of last year and up over 200 basis points sequentially.
In terms of operating expenses, we're continuing to invest heavily into sales and marketing and research and development as we look to capitalize on the technological advantage of our platform and our expanding market opportunity.
In the quarter, we invested in our sales force expansion, staffing support, operating infrastructure and cycle management to support our increasing volume and our growing engagement with the reimbursement market. We added 5 experienced sales professionals, bringing our ramp sales and marketing team to 10 professionals and expanded our sales footprint into new regions while further penetrating existing markets.
Despite these investments, our GAAP operating margins were in excess of 20% in the quarter. Excluding stock-based compensation, non-GAAP operating margins were over 30%. We believe we have lots of excess capacity and can demonstrate further leverage as we continue to bring down COGS in 2017.
Adjusted EBITDA for the quarter was $2.3 million or approximately 40% of revenues. On a non-GAAP basis and excluding stock-based compensation, income for the quarter was $1.1 million versus $0.06 per share on 17.8 million shares outstanding. The tax rate at the end of the fourth quarter was 38%.
And looking at our balance sheet, we're well capitalized to support our growth and expansion plans. We entered 2017 with a strong liquid balance sheet with no debt. We have excess capacity and minimal capital expenditure needs and expect to generate positive cash flow and profits through 2017 even as we continue to invest heavily in core business. For the full year 2016, revenue roughly doubled from 2015, and the number of billable tests grew from approximately 6,800 to approximately 12,500.
As we look into 2017, we expect to continue the rapid growth we have seen in our business. We should be able to collect on almost all of our billable tests and anticipate the number of collectible tests in 2017 to more than double versus the total billed in 2016. We expect to see continued strength in our core hospital market and more traction with reimbursement. In addition, we see multiple opportunities with research institutions via pharma organizations and larger labs. We expect some of these opportunities could provide additional upside to our business in 2017.
As Ming indicated in prior, the progress with our joint venture with Xi Long, some of our Asian customers have begun sending tests to our lab in China. We see tremendous potential in our positioning and partnership with Xi Long in 2017 and beyond. We also see lots of untapped opportunity abroad in areas such as Europe, the Middle East, Australia and Canada and continued expansion in international business.
In sum, with collectible tests at least doubling the number of 2016 billable tests and with conservative assumptions about [ ASPs to clients ], which we haven't experienced yet, we expect revenue for 2017 to be in the range of $30 million to $36 million, which represents a year-over-year growth of 65% to close to 100%.
For Q1, we expect revenue to be roughly flat sequentially and up approximately 70% year-over-year. As our Asian customers increasingly send samples directly to our JV partners in Asia, we will not see this revenue contribution directly and instead recognize this value to our joint venture investment. Based on the revenue we generated from our Asian customers in Q4, we expect this dynamic will have an impact of $1 million to $2 million on our top line revenue in the first quarter, and we have factored this into our guidance.
Also, please note that although we expect to see royalty payments from our joint venture with Xi Long over the course of the year, we have not incorporated this uplift into our guidance. Even with the assumptions regarding the price declines and continued investment, we see non-GAAP gross and operating margins for 2017 in excess of 65% and 30%, respectively. We also see upside to these margins as price declines have not materialized for our business as we continue to broaden our offerings and look furthering into our technology beyond genes and panels.
We also have excess capacity and have yet capitalize on operational efficiencies. With the well-capitalized balance sheet, with cash and investment in excess of $46 million along with the business that produces GAAP profits and positive cash flow, armed with technology and a rich project portfolio in a huge addressable market, we look forward to achieving record returns.
Operator, you can now open it up for questions.