Glenn A. Eisenberg
Executive Vice President and Chief Financial Officer at Laboratory Co. of America
Thank you, Adam. I'm going to start my comments with a review of our second quarter results, followed by a discussion of our performance in each segment and conclude with an update on our full year guidance. Revenue for the quarter was $3.8 billion, an increase of 38.7% over last year due to organic growth of 35.5%, acquisitions of 1.2% and favorable foreign currency translation of 200 basis points. Our organic base business increased 42.4% when compared to our base business last year, while COVID testing revenues of $444 million were flat with last year.
Operating income for the quarter was $704 million or 18.3% of revenue. During the quarter, we had $92 million of amortization and $43 million of restructuring charges and special items. Excluding these items, adjusted operating income in the quarter was $840 million or 21.9% of revenue compared to $381 million or 13.8% last year. The increase in adjusted operating income and margin was primarily due to organic base business growth, acquisitions and LaunchPad savings, partially offset by higher personnel costs.
During the second quarter, interest expense was $78 million, up from $53 million last
Year. The increase was due to onetime costs associated with the company's refinancing of $1 billion in senior notes that were due to mature in 2022, taking advantage of the historically low interest rate environment. Excluding these onetime costs, interest expense would have been down $7 million versus last year due to lower debt levels and interest rate.
The tax rate for the quarter was 28.1%. The adjusted tax rate, excluding restructuring charges, special items and amortization, was 25.1% compared to 23.9% last year. The higher adjusted tax rate was primarily due to the geographic mix of earnings. We continue to expect our full year adjusted tax rate to be approximately 25%. Net earnings for the quarter were $467 million or $4.76 per diluted share. Adjusted EPS, which exclude amortization, restructuring charges and special items, were $6.13 in the quarter, up from $2.57 last year. Operating cash flow was $487 million in the quarter compared to $371 million a year ago.
The increase in operating cash flow was due to favorable working capital, partially offset by lower cash earnings. Capital expenditures totaled $97 million or 2.5% of revenue compared to $99 million or 3.6% of revenue last year. As a result, free cash flow was $390 million in the quarter compared to $272 million last year. During the quarter, we used $300 million of our cash flow for our share repurchase program. Now I'll review our segment performance, beginning with Diagnostics.
Revenue for the quarter was $2.4 billion, an increase of 39.7% compared to last year due to organic growth of 37.8%, acquisitions of 1.1% and favorable foreign exchange translation of 90 basis points. Organic base business growth was 51.2% compared to our base business last year, while COVID testing revenues were flat versus last year. Relative to the second quarter of 2019, the compound annual growth rate for the base business revenue was 4.5% primarily due to organic growth.
Total volume increased 39.6% over last year primarily due to organic volume growth of 38.7%. The increase in organic volume was due to a 39.4% increase in the base business, partially offset by a reduction in COVID testing of 0.7%. As a reminder, we do not include hospital lab management agreements in our volume, which would have added approximately 3.3% to organic base business volume growth. Price/mix increased 0.1% over last year due to currency of 0.9%, COVID testing of 0.7% and acquisitions of 0.2%, partially offset by organic base business of minus 1.7% due to mix associated with the volume recovery.
Of Diagnostics organic base business revenue growth of 51.2% compared to its base business last year, 48.2% was driven by volume, while 3.1% was from price mix, which was due to an increase in test per accession. Diagnostics adjusted operating income for the quarter was $663 million or 28% of revenue compared to $309 million or 18.2% last year.
The increase in adjusted operating income and margin was primarily due to organic base business demand and LaunchPad savings, partially offset by higher personnel costs. Relative to the second quarter of 2019, base business margins were down slightly due to the negative impact from PAMA. Diagnostics margins were down in the second quarter of this year compared to the first quarter due to lower COVID testing, while base business margins increased. Diagnostics three year LaunchPad initiative remains on track to deliver approximately $200 million of net savings by the end of this year.
Now I'll review the performance of Drug Development. Revenue for the quarter was $1.5 billion, an increase of 36.7% compared to last year due to organic growth of 31.8%, acquisitions of 1.3% and favorable foreign currency translation of 370 basis points. Drug Development delivered broad-based revenue growth across all businesses, including COVID vaccine and therapeutic studies. Relative to the second quarter of 2019, the compound annual growth rate for the base business revenue was approximately 15% primarily driven by organic growth.
Adjusted operating income for the segment was $221 million or 14.8% of revenue compared to $113 million or 10.3% last year. The increase in adjusted operating income and margins were primarily due to organic base business demand and LaunchPad savings, partially offset by higher personnel costs. Relative to the second quarter of 2019, base business margins were up approximately 200 basis points. While second quarter margins this year were lower than first quarter, we expect our second half base business margins to be up versus the first half. We also expect our full year margins this year to be up over 2020, which was up over 2019.
For the trailing 12 months, net orders and net book-to-bill remained strong at $7.9 billion and 1.41, respectively. Backlog at the end of the quarter was $14.3 billion, an increase of approximately $300 million from last quarter. We expect approximately $4.9 billion of this backlog to convert into revenue over the next 12 months. Now I'll discuss our 2021 full year guidance, which assumes foreign exchange rates effective as of June 30, 2021, for the full year.
We are raising our full year guidance to reflect the company's strong second quarter performance and improved outlook for the remainder of the year for both our Diagnostics and Drug Development base businesses. We expect enterprise-level revenue to grow 6.5% to 9% from prior guidance of 2% to 6.5%. This includes the benefit from foreign currency translation of 100 basis points. This guidance range also includes the expectation that the base business will now grow 17% to 19%, while COVID testing is expected to be down 38% to down 33%.
We are raising our expectations for revenue in Diagnostics to minus 1% to plus 2% from prior guidance of minus 5% to flat. This guidance range includes the expectation that the base business will now grow 15% to 17%, while COVID testing revenue is now expected to be down 38% to down 33%. We are also raising our growth expectations for revenue in Drug Development to 17% to 19% from prior guidance of 12% to 14%.
Our current guidance includes the benefit from foreign currency translation of 200 basis points. This guidance range also includes the expectation that the base business will now grow 19% to 21%. Given the improved top line growth expectations of our base businesses, we are raising our adjusted EPS guidance to $21.5 to $25, up from prior guidance of $20 to $24. Free cash flow is now expected to be between $1.95 billion to $2.15 billion, up from prior guidance of $1.8 billion to $2 billion. Earnings guidance assumes we will use our free cash flow for acquisitions and share repurchases, which we expect to accelerate in the second half of the year.
We expect that capital expenditures will be approximately 3.5% to 4% of revenue driven by investments to support base business growth and productivity. For additional comparison purposes, we have also included, in the supplemental deck on our Investor Relations website, a view of 2021 second quarter results and full year guidance compared to 2019 results. In summary, the company had another quarter of strong performance.
We remain focused on performing a critical role in response to the global pandemic while also growing our base business. As we progress through 2021, we expect to drive continued profitable growth in our base business, while COVID testing volumes are expected to decline in the second half. We expect to continue to use our free cash flow generation for acquisitions that supplement our organic growth, while also returning capital to shareholders through our share repurchase program.
Operator, we will now take questions.