Hospital operator HCA ( HCA) pushed up fourth-quarter earnings guidance Wednesday after updating its methodology for calculating doubtful accounts. HCA expects to earn 68 cents to 72 cents a share in the three months ended Dec. 31, up from its previous estimate of 52 cents to 57 cents a share. It left its revenue estimate alone at $5.9 billion. Wall Street was expecting earnings of 55 cents a share on revenue of $5.92 billion, according to Thomson First Call. "Financial results benefited from the company's refinements to the provision for doubtful accounts estimation process, reductions to the effective tax rate and reductions in shares outstanding" that resulted from a $2.5 billion Dutch auction completed in November. HCA expects to put up a $626 million provision for doubtful accounts in the quarter. The figure was reduced by $46 million, or about 6 cents a share, by the estimate refinement, which primarily related to estimated recoveries associated with Medicare co-pays and deductibles and collection agency placements. On a preliminary basis, the company put fourth-quarter same-facility admissions down 1.4% in the quarter, and said same-facility equivalent admissions rose 0.1% from a year ago. Same-facility revenue rose about 6.5% from a year ago. In addition, the company's effective tax rate was adjusted in the fourth quarter, cutting the period's tax bill by $19 million, or 4 cents a share. The stock rose $2.31, or 5.8%, to $41.99 in premarket Instinet trading.