Ron Bruehlman
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 $3,868 million grew 3.5% on a reported basis and 2.6% at constant currency. In the quarter, COVID-related revenues were approximately $65 million, which was down about $125 million versus the fourth quarter of 2022. Now, excluding all COVID-related work from both this year and last, constant currency growth was approximately 6% and as already mentioned, acquisitions contributed about 150 basis points to this growth.
Technology & Analytics Solutions revenue for the fourth quarter was $1,531 million up 2.1% reported and 1.3% constant currency. Excluding all COVID-related work, constant currency growth in TAS was 4%. R&D Solutions fourth quarter revenue of $2,151 million was up 4.5% reported and 3.7% at constant currency. And excluding all COVID-related work, constant currency growth and R&DS was 9% in the quarter.
Finally, Contract Sales & Medical Solutions, or CSMS fourth quarter revenue, up $186 million grew 2.2% reported and 1.7% at constant currency. For the full year, revenue was $14,984 million growing at 4% on a reported basis and 4.1% at constant currency. COVID-related revenues totaled approximately $420 million for the year. Excluding all COVID-related work from both years, constant currency growth was 9%. Full year Technology & Analytics Solutions revenue was $5,862 million up 2% reported, 2.1% at constant currency and excluding all COVID-related work, growth at constant currency in TAS was 6%.
In R&D Solutions, full year revenue was $8,395 million growing 6% both on a reported and a constant currency basis and excluding all COVID-related work, growth at constant currency and R&DS was 13%. Finally, in CSMS, revenue for the full year was $727 million which was down 2.2% reported and 0.3% at constant currency.
Moving down the P&L, adjusted EBITDA was $966 million for the fourth quarter, that represented 5% growth, while full year adjusted EBITDA was up 6.7% year-over-year.
Fourth quarter GAAP net income was $469 million and GAAP diluted earnings per share was $2.54. For the full year, GAAP net income was $1,358 million or $7.29 of earnings per diluted share. Adjusted net income was $523 million for the fourth quarter and adjusted diluted earnings per share was $2.84. For the full year, adjusted net income was $1,901 million and adjusted diluted EPS was $10.20. Excluding the year-over-year impact of the step up in interest rates and the increase in the U.K. corporate tax rate, adjusted diluted earnings per share grew 11% in the fourth quarter and 12% for the full year.
Now, as Ari reviewed, R&D Solutions delivered another really strong quarter of bookings. Our backlog at December 31 stood at a record $29.7 billion. That's up 9.2% year over year and 31% over the last three years.
Let's turn to the balance sheet. As of December 31, cash and cash equivalents totaled $1,376 million and gross debt was $13,673 million and do the math that results in net debt of $12,297 million. Our net leverage ratio at year end was 3.45 times trailing 12-month adjusted EBITDA. Fourth quarter cash flow from operations was $747 million and capital expenditures was $179 million, which resulted in free cash flow of $568 million for the quarter. Now, in the quarter, we repurchased $229 million of our shares at an average price of $1.95 per share, bringing our full-year share repurchase activity to just slightly below $1 billion. This leaves us with just under $2.4 billion of share repurchase authorization remaining under the current program.
Now, as you know, coming out of the merger, we took advantage of the low interest rate environment and deployed a significant amount of capital for internal investments, acquisitions and share repurchases, which were quite accretive for our shareholders. Now, over that period, our net interest expense was relatively steady at around $400 million per year. But at the end of 2022 and through the middle of 2023, we experienced a rapid and unprecedented rise in interest rates, which drove annual interest expense up by $250 million [Phonetic] causing our adjusted EPS to be just slightly over flat in 2023. Now, as you saw in November, we successfully refinanced approximately $2.75 billion of our near-term debt maturities. The strong demand for IQVIA debt that we experienced allowed us to tighten pricing and lock in an average fixed rate below 4.9% for those issuances after swaps. This refinancing extended approximately $2.75 billion of maturities to 2029 and 2031, and we reduced our interest rate risk exposure by locking in over 80% of our debt at fixed rates.
With this refinancing, we now expect net interest expense to be approximately $650 million in 2024. Now, the forward curves point to a reduction in rates in the future, we've included the current [Indecipherable] consensus in our 2024 guidance. Further reductions would lower our net interest expense more on our variable rate debt and potentially open opportunities to refinance additional debt in the future.
Now let's go to our 2024 guidance, which I'll review in detail. For the full year, we expect total revenue to be between $15,400 million and $15,650 million. This includes approximately $300 million of a step down in COVID-related work year over year and about 100 basis points of contribution from M&A activity and further FX headwind of approximately 50 basis points versus 2023.
Our adjusted EBITDA guidance is $3,700 million to $3,800 million. Our adjusted diluted EPS guidance is $10.95 to $11.25. Now this guidance includes about $650 million of interest expense, approximately $580 million of operational depreciation and amortization expense, an effective income tax rate just under 20% and an average diluted share count of approximately 184 million shares. This guidance also assumes about $2 billion of cash deployment, split evenly between acquisitions and share repurchase.
Finally, our guidance assumes that foreign currency rates as of February 12th continue for the balance of the year. Now, at the segment level, we expect TAS revenue to be between $6 billion and $6.2 billion. Q1 2023 was the last quarter that we had significant COVID-related revenues and TAS. So the COVID step-down in TAS will be minimal for the balance of the year. As Ari mentioned, the guidance now anticipates an improvement in our commercial business towards the back end of the year, which will still result in a year-over-year growth of low-to-mid single digits. R&DS revenue is expected to be between $8.7 billion and $8.8 billion. This guidance includes almost the entire $300 million step-down in COVID-related revenue and that represents approximately 350 basis points of headwind to the R&DS growth rate.
The guidance also reflects the latest phasing of pass-through revenue, which results in an additional headwind of approximately 100 basis points to R&DS year-over-year. Adjusting for the COVID stepdown in the pass-through headwind, R&DS revenue growth in 2024 is expected to remain in the high-single digits. CSMS revenue is expected to be approximately $700 million, which is down slightly year-over-year.
Now let's review the first quarter guidance. For the first quarter, we expect revenue to be between $3,650 million and $3,725 million. The decline in COVID-related work is weighted towards the beginning of the year with the largest impact in Q1. Also, we expect market conditions and TAS to recover only in the back half of the year, as we've said. Adjusted EBITDA in the first quarter is expected to be between $850 million and $870 million and adjusted diluted EPS is expected to be between $2.45 and $2.55. Now keep in mind that Q1 is the toughest comparison for adjusted diluted EPS due to the interest rate increases we saw throughout 2023. As we mentioned, our guidance assumes that foreign currency rates as of February 12th continue for the balance of the year.
So let's summarize, Q4 was another strong quarter. R&DS delivered the second largest booking quarter in IQVIA history at over $2.8 billion, along with another quarter of double-digit RFP growth. For the full year of 2023, revenue grew 9% at constant currency, excluding COVID-related work. Our EBITDA margin expanded by 60 basis points and adjusted diluted EPS was up 12% if you exclude the year-over-year impact of interest rates in the increase in the U.K. tax rate. Free cash flow was strong in the quarter at $568 million, representing 109% of adjusted net income. IQVIA was named to Fortune's 2023 list of the World's most Admired Companies for the seventh consecutive year and earned the first place ranking within our industry group for the third consecutive year.
And lastly, we issued full-year 2024 guidance with underlying revenue growth of 5% to 7%, continued margin expansion and a resumption of EPS growth with adjusted diluted earnings per share expected to be up 7% to 10%.
Now, before we open the call to Q&A, I'd like to make you aware of the leadership change within IQVIA's finance organization, Nick Childs, who has led our Investor Relations and Treasury functions very ably for the past three years, is moving on to become CFO of our North American business. He will be succeeded by Kerry Joseph, who has served as CFO of that business unit for the past five years. Kerry, who is a member of the global finance leadership team has had many finance roles and increasing responsibility during his 20-plus years with the company. Kerry and Nick have already been working together to transition responsibilities and Kerry will join Nick on our follow-up calls this quarter, so you all have a chance to meet them.
Now, with that, let me hand it back over to the operator to begin our Q&A session.