Second, revenue growth. Revenue increased 4% year-over-year in the first quarter. During the quarter, revenue per requisition increased 1.2% year-over-year. Total company volume increased 2.8% year-over-year during the first quarter.
Esoteric volume increased 4.8% in the quarter. The quarter benefited from an easier weather comp, which increased the revenue and volume growth rate by 1.5%. Although there was an extra calendar day in the quarter, the strength of days in the quarter was approximately the same as last year.
Third, margin. For the first quarter, our adjusted operating income margin was 19.9% compared to 19.3% in the first quarter of 2011. We are very pleased with the margin improvement, which reflects the positive impact from our integration activities. Fourth, liquidity. We remain well-capitalized. At the end of March, we had cash of $129.9 million and $500 million available under our revolving line of credit.
During the first quarter, we repurchased $122.3 million of stock representing 1.4 million shares. At the end of March, $462.1 million of repurchase authorization remained under our share repurchase program. This morning, we also reiterated our 2012 financial guidance. We expect revenue growth of 2% to 3.5%, adjusted EPS excluding amortization in the range of $6.75 to $7.05, excluding the impact of any share repurchase activity after March 31, 2012, operating cash flow of approximately $950 million and capital expenditures of approximately $155 million.I'll now turn the call over to Dave. David P. King Thank you, Brad. We are very pleased with our first quarter 2012 results. We generated strong revenue growth. We delivered solid increases in core and esoteric volume. Revenue per requisition increased 1.2%. We lowered our bad debt rate to 4.4% during the quarter, reflecting the continued exceptional performance of our operational and billing personnel. Read the rest of this transcript for free on seekingalpha.com