Executive Vice President and Chief Financial Officer at IQVIA
Thanks, Ari, and good morning, everyone. Let's start by reviewing revenue. Fourth quarter revenue of $3,636 million grew 10.2% on a reported basis and 11.6% at constant currency. You'll recall that last year's fourth quarter was a much tougher comparison than earlier quarters as we picked up incremental demand for mega vaccine studies in R&DS in government-related COVID work within TAS. Also, the core business began to rebound from the effects of COVID-19.
In this year's fourth quarter, COVID-related revenues were approximately $325 million, down about 25% versus the fourth quarter of 2020. In our base business, that is excluding all COVID-related work from both 2021 and 2020, organic growth at constant currency was mid-teens. Technology and Analytics Solutions revenue for the fourth quarter was $1, 496 million, up 5% reported and 6.6% at constant currency. Year-over-year, TAS experienced just over 400 basis points of headwind due to a step down in COVID-related work. Excluding all COVID-related work, organic growth at constant currency in TAS was high-single digits.
R&D Solutions fourth quarter revenue of $1,944 million was up 15.4% at actual FX rates and 16.3% at constant currency. Excluding all COVID-related work, organic growth at constant currency and R&DS was approximately 25%. Contract Sales and Medical Solutions or CSMS fourth quarter revenue of $196 million grew 3.7% reported and 7.4% at constant currency. Excluding all COVID-related work, organic growth at constant currency and CSMS was low single digit.
For the full year, revenue was $13, 874 million, growing at 22.1% reported and 21.1% at constant currency. COVID-related revenues in 2021 were approximately $1.8 billion, with just under 80% of that attributable to R&DS, about 20% due to TAS and the remainder in CSMS. The incremental COVID-related revenues in 2021 versus 2020 accounted for approximately half of our growth in 2021.
Full year Technology and Analytics Solutions revenue was $5, 534 million, up 13.9% reported and 12.4% at constant currency. Excluding COVID-related work, organic growth at constant currency and TAS was high single-digit. Full year revenue in R&D Solutions with $7, 556 million, growing at 312% reported and 30.4% at constant currency. Excluding COVID-related work, R&DS organic growth at constant currency for both total revenue and services revenue was low double-digit. Full year CSMS revenue was $784 million, representing 5.8% growth on a reported basis and 5.7% at constant currency and excluding COVID-related work, organic growth at constant currency and CSMS was low single digit.
Now moving down to P&L, adjusted EBITDA was $828 million for the fourth quarter, which was 12.7% growth on a reported basis. Full year adjusted EBITDA was $3,022 million, up 26.8% year-over-year on a reported basis. Fourth quarter GAAP net income was $318 million and GAAP diluted earnings per share was $1.63. Full year GAAP net income was $966 million or $4.95 of earnings per diluted share. Adjusted net income was $496 million for the fourth quarter, up 20.7% year-over-year and adjusted diluted earnings per share grew 20.9% to $2.55. For the full year, adjusted net income was $1, 760 million or $9.03 per share, up 41%.
Now, as already reviewed, R&D Solutions delivered another outstanding quarter of net new business, R&DS backlog now stands at a record $24.8 billion, an increase of 10.2% year-over-year. Full year 2021 net new bookings including pass-throughs road over 10 -- rose to over $10 billion for the first time, that's 14.6% growth compared to 2020.
Okay, lets now move to the balance sheet now. Our cash flow was again quite strong in the quarter. Cash flow from operations was $692 million and capex was $184 million, which resulted in free cash flow of $508 million. This brought our free cash flow for the full year to a record $2.3 billion, up 17% [Phonetic] versus the prior year. At December 31, cash and cash equivalents totaled $1, 366 million and gross debt was $12,125 million, resulting in net debt of $10, 759 million. Our net leverage ratio at December 31 was 3.5 6 times trailing 12 month adjusted EBITDA.
Now it's worth highlighting that our improved free cash flow over the last two years allowed us to deploy approximately $4.5 billion of capital to internal investments, acquisitions and share repurchase, while at the same time, we were able to reduce our net leverage ratio from a high of 4.8 times in Q2 2020, which you'll recall was the height of the pandemic to nearly 3.5 times. And in doing this, we achieved our vision '22 net leverage ratio target of 3.5 times to 4 times a full year early.
In the quarter, we repurchased $174 million of our shares, which resulted in full year share repurchase of $395 million, and we ended the year with 195 [Phonetic] million fully diluted shares outstanding and $523 million of share repurchase authorization remaining under our existing program. Now, last week, our Board of Directors approved a $2 billion increase to our share repurchase authorization, which increases our remaining authorization to just over $2.5 billion.
Now let's turn to the guidance. As you saw, we are reaffirming the full year 2022 revenue guidance that we issued at our Analyst and Investor Conference in November and in maintaining this guidance, we actually absorbed a $70 million revenue headwind from FX, since we initially guided in November. Now additionally, we're raising our full year 2022 profit guidance versus what -- versus what we provided to you in November. So, to summarize, the overall guidance for the full year we expect revenue to be between $14, 700 million and $15 billion, which represents year-over-year growth of 7.1% to 9.2% at constant currency and 6% to 8.1% on a reported basis compared to 2020. Now, we now expect adjusted EBITDA to be between $3,330 million and $3, 405 million, representing year-over-year growth of 10.2% to 12.7%. And we also now expect adjusted diluted EPS to be between $9.95 and $10.25, which represents year-over-year growth of 10.2% to 13.5%.
Now our full year 2022 guidance assumes that December 31, 2021 foreign currency exchange rates will remain in effect for the balance of the year. Now compared to the prior year, I should mention that FX is now a headwind of 110 basis points to our full year revenue growth. And our projected revenue growth includes a little bit over 100 basis points of contribution from M&A activity.
Now in our Analyst and Investor Conference in November we told you to anticipate that our COVID-related revenue will step down by approximately $1 billion in 2022, but we'll more than compensate for that headwind with strong growth in our base business and let me give you some additional detail around this and I think will be helpful. Excluding COVID-related revenue, the FX headwind and the contribution of acquisitions, our total company revenue guidance implies organic growth at constant currency in the low-to-mid-teens. At the segment level, we anticipate full year Technology and Analytics Solutions revenue growth of between 5% and 7%. Excluding COVID-related work, we expect organic revenue growth at constant currency in TAS's to be in the high single digits.
Research and Development Solutions revenue growth is expected to be between 8% and 10%. Excluding COVID-related work, we expect organic revenue growth at constant currency in R&DS to be in the upper teens. And finally, Contract Sales and Medical Solutions revenue was anticipated to be down about 2%, but excluding COVID-related work, we expect organic revenue growth at constant currency and CSMS to be in the low single digits.
Let's move to the first quarter now. As you all know, the first quarter of last year marked a continued rebound in our base business after the 2020 pandemic-related decline. In addition, Q1 and Q2 of last year represented our peak COVID-related revenues. And as a result of this, the first half of the year will have the most challenging year-over-year compares. For the first quarter, our revenue was expected to be between $3,515 million and $3, 575 million, representing growth of 4.8% to 6.6% on a constant currency basis and 3.1% to 4.9% or a reported basis. Now excluding COVID-related work, we expect organic revenue growth at constant currency to be in the mid teens. Adjusted EBITDA is expected to be between $800 million and $815 million, up 7.5% to 9.5%. And finally, adjusted diluted EPS is expected to be between $2.40 and $2 2.46, growing 10.1% to 12.8%.
So, to summarize, we delivered very strong fourth quarter results on both the top and bottom line against what was also a very strong fourth quarter of 2020. R&DS recorded its largest-ever quarter of service bookings and for the first time had over $10 billion of total net new bookings in a year. Our contracted backlog improved to a record of nearly $25 billion, up over 10% year-over-year, and we delivered another strong quarter of free cash flow, bringing the full year to a record $2.3 billion. We closed 2021 with net leverage of 3.6 times trailing 12-month adjusted EBITDA. Our Board approved a $2 billion increase to our share repurchase authorization. And finally, we are reaffirming the full year 2022 guidance that we provided in November to revenue and we're raising our adjusted EBITDA and adjusted diluted EPS guidance.
And with that, let me turn it back over to the operator for questions-and-answers.