Answering your question on blood film reviews.

Blood film reviews

Q Our hematology laboratory is in the process of reviewing and evaluating the criteria we use to trigger blood film reviews. We have developed tentative flagging criteria, which we will evaluate against previous results on 200 patients to determine which abnormalities might have been missed if we had used these new criteria. What is the most efficient way to compile and access these data? Can you provide any information on the best way to approach such an analysis? What would be considered an acceptable false-negative rate? How frequently must actual blood films be reviewed when consecutive specimens are flagged?

A You may have read the four-part series of articles, "Streamline your hematology laboratory," which appeared in the December 1996 (p. 50), January 1997 (p. 58), February (p. 43), and April (p. 68) issues of MLO. The three discussants, Dr. Cornbleet, Dr. Fernandes, and Martha Miers, give many practical suggestions for the implementation of methods that improve the efficiency of hematology laboratories without compromising patient care.

A number of publications have covered this topic in some detail. For instance, a November 1994 MLO article ("Let's improve the flagging of abnormal hematology specimens," p. 22) includes about 30 pertinent references. Since then, a host of more recent models of instruments have been evaluated for their flagging capabilities. One analyzer even quantitates nucleated red cells, which were previously only flagged. Contact the manufacturer to request copies of such studies, either in the published literature or in-house evaluations.

The success of your review of blood film review criteria depends on the hematology analyzer being used in your laboratory to flag these specimens because there are instrumental differences in the efficiency of the flagging rates, and depending on the case mix in your particular laboratory, such differences may or may not become apparent. If you do a comparison with the last 200 cases, the results could vary depending on the types of cases that have been included. If many of the cases were outpatients in reasonably good health, the efficiency would most likely be very good. In the hematology clinic or inpatient service, the results might not be as convincing. But any comparison study that includes all of the individuals who perform blood film reviews in your laboratory would at least serve as a good way to involve and educate the entire technical staff.

The NCCLS working party that is developing guidelines for flagging and blood film reviews has tentatively said that there should be a 90% sensitivity and a 90% specificity for specific abnormalities. Some instruments are close to those goals. But again, the case mix may have a significant effect on these statistical parameters.

When we implemented a flagging program, we noted that some patients had daily or even hourly blood counts requested. Examples included post-operative cases or major trauma cases. It was obvious that such re-reviews were not very useful, so we also developed practice guidelines for such cases. Essentially, one can use delta checking techniques. In other words, if the red cell parameters, leukocyte count (including the instrumental differential) or the platelet count did not change significantly, we did not require another film review.

Delta checking systems are being developed. Some instruments have large integral blood count data bases against which current blood counts can be compared. However, if there are several instruments being used in the laboratory or in point-of-care units outside the laboratory, the delta checking should be incorporated into the LIS or HIS to be effective.