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 third 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 $4.1 billion, an increase of 4.3% over last year due to organic growth of 3.4%, acquisitions of 0.4% and favorable foreign currency translation of 50 basis points.
The 3.4% increase in organic revenue is driven by a 10.2% increase in the company's organic Base business partially offset by a 6.8% decrease in COVID testing. Operating income for the quarter was $767 million or 18.9% of revenue. During the quarter, we had $92 million of amortization and $48 million of restructuring charges and special items. Excluding these items, adjusted operating income in the quarter was $907 million or 22.3% of revenue compared to $1.2 billion or 29.7% last year.
The decrease in adjusted operating income and margin was due to a reduction in COVID testing as well as higher personnel costs resulting from increased Base Business demand and a tight labor market as the company continues to invest in its workforce. Partially offsetting these headwinds were the benefit from organic Base Business growth and LaunchPad savings. The tax rate for the quarter was 23.5%. The adjusted tax rate, excluding restructuring charges, special items and amortization, was 24.4% compared to 25.7% last year.
The lower adjusted 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 $587 million or $6.05 per diluted share. Adjusted EPS, which exclude amortization, restructuring charges and special items, were $6.82 in the quarter, down from $8.41 last year. Operating cash flow was $767 million in the quarter compared to $786 million a year ago.
The decrease in operating cash flow was due to lower cash earnings partially offset by favorable working capital. Capital expenditures totaled $118 million or 2.9% of revenue compared to $77 million or 2% of revenue last year. As a result, free cash flow was $650 million in the quarter compared to $709 million last year. During the quarter, we used $300 million of our cash flow for our share repurchase program and invested $292 million on acquisitions.
Now I'll review our segment performance, beginning with Diagnostics. Revenue for the quarter was $2.6 billion, a decrease of 3.2% compared to last year due to organic revenue being down 3.9%, partially offset by acquisitions of 0.4% and favorable foreign currency translation of 30 basis points. The decrease in organic revenue was due to a 9.7% reduction from COVID testing partially offset by a 5.8% increase in the Base Business. Relative to the third quarter of 2019, the compound annual growth rate for Base Business revenue was 4.7%, primarily due to organic growth.
Total volume increased 0.2% over last year as acquisition volume contributed 0.2% and organic volume decreased by 0.1%. The decrease in organic volume was due to a 5.9% decrease in COVID testing partially offset by a 5.9% increase in the Base Business. As a reminder, we do not include hospital lab management agreements in our volume, which would have added approximately 1.1% to our organic Base Business volume growth.
Price/mix decreased 3.4% versus last year due to lower COVID testing of 3.8% partially offset by currency of 0.3% and acquisitions of 0.2%. Diagnostics organic Base Business revenue growth was 9% compared to its Base Business last year, with 7.7% coming from volume and 1.3% coming from price/mix, which was primarily due to an increase in test per session. Diagnostics adjusted operating income for the quarter was $775 million or 29.6% of revenue compared to $1 billion or 37.1% last year.
The decrease in adjusted operating income and margin was primarily due to a reduction of COVID testing and higher personnel costs partially offset by organic Base Business growth and LaunchPad savings. Relative to the third quarter of 2019, Base Business margins were down slightly due to the negative impact from PAMA. 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 17.5% compared to last year due to organic Base Business growth of 19.9%, acquisitions of 0.4% and favorable foreign currency translation of 100 basis points. This was partially offset by lower COVID testing performed through its central lab business of 3.5% and divestitures of 0.3%. Drug Development's Base Business benefited from broad-based growth across all businesses, including COVID vaccine and therapeutic work.
Relative to the third quarter of 2019, the compound annual growth rate for Base Business revenue was 11.4% primarily driven by organic growth. Adjusted operating income for the segment was $226 million or 15.5% of revenue compared to $210 million or 16.9% last year. The increase in adjusted operating income was primarily due to organic Base Business growth and LaunchPad savings partially offset by lower COVID testing and higher personnel costs.
The decline in adjusted operating margin was due to lower COVID testing. Excluding the impact from COVID testing, operating margins would have been up compared to last year. For comparability to peers, Drug Development earnings exclude $36 million of expense related to the enterprise component of its bonus, which is included in unallocated corporate expense. We expect full year margins to be up over 2020, which were up over 2019. For the trailing 12 months, net orders and net book-to-bill remained strong at $7.8 billion and 1.34, respectively.
During the quarter, orders were negatively impacted by approximately $150 million due to a significant scope change, which decreased the book-to-bill. Backlog at the end of the quarter was $14.4 billion, an increase of 15.4% compared to last year. 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 September 30, 2021, for the remainder of the year.
We are raising our full year guidance to reflect the company's strong third quarter performance and improved outlook for the remainder of the year. We expect enterprise revenue to grow 13% to 14% from prior guidance of 6.5% to 9%. This includes the benefit from foreign currency translation of 90 basis points. This guidance range also includes the expectation that the Base Business will grow 18.5% to 19.5%, while COVID testing is expected to be down 11% to down 6%.
We are raising our expectations for revenue to grow in Diagnostics by 8% to 10% from prior guidance of minus 1% to plus 2%. This guidance range includes the expectation that the Base Business will grow 16% to 17%, while COVID testing revenue is expected to be down 11% to down 6%. We're also raising our growth expectations for revenue in Drug Development to 19.5% to 20.5% from prior guidance of 17% to 19%. Our current guidance includes the benefit from foreign currency translation of 170 basis points.
This guidance range also includes the expectation that the Base Business will grow 21.5% to 22.5%. Given the improved top line growth expectations, we are raising our adjusted EPS guidance to $26 to $28, up from prior guidance of $21.5 to $25. Free cash flow is now expected to be between $2.45 billion to $2.6 billion, up from prior guidance of $1.95 billion to $2.15 billion. For additional comparison purposes, we've also included in the supplemental deck on our Investor Relations website a view of 2021 third 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. We expect to drive continued profitable growth in our Base Business, while COVID testing volumes are expected to decline through the remainder of the year. 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 programs.
Operator, we will now take questions.