NICU NEWS: STATE LAB FALSE POSITIVES AND SANI-WIPES

NEW YORK (Reuters Health) Oct 18 - Contamination of dried blood spot specimens by sanitary wipes can lead to false-positive diagnosis of malonic aciduria, a rare enzyme deficiency.

"I believe that it is very important to convey findings such as ours to newborn nurseries across the country," Dr. Bailey A. Reindl from Sanford School of Medicine of the University of South Dakota, Sioux Falls, South Dakota told Reuters Health.

"There are many points in the newborn screening process in which pre-analytical, analytical, and post-analytical errors can occur, and it is important for the clinician to realize this," Dr. Reindl added.

After seeing 10 false-positive cases of malonic aciduria over a seven-month period, Dr. Reindl and colleagues investigated the dried blood spot collection process used by their newborn nursery staff.

As reported Monday in Pediatrics, they found that the filter paper used for blood collection had been placed on a countertop that had recently been sanitized using a Sani-Cloth wipe (a recent change from a different disinfectant).

Dilutions of up to 1:50 of the Sani-Cloth disinfectant produced elevations in the mass spectrometry analysis for malonylcarnitine (C3-DC) to levels above the newborn cutoff of 0.20 microM, levels similar to those in the 10 false-positive cases.

"Therefore," the researchers note, "it was possible that the falsely elevated C3-DC level was caused by only a few microliters of undiluted disinfectant within the dried blood specimen."

Although the investigators have yet to determine the mechanism by which the chemicals derived from the disinfectant interfere with the mass spectrometry analysis, there have been no false-positive C3-DC results since the investigative process (and review of the proper technique for filter paper blood collection with nursing staff).

"By our estimates, the average cost for a false-positive screen at our institution was approximately $694 after confirmatory testing was completed," Dr. Reindl said. "This is a significant expense for a family with a newborn child to pay on unnecessary testing that could have been avoided by the use of proper blood collection techniques and specimen handling."

"In our situation clinicians, newborn nursery personnel, laboratory personnel and administrators from the newborn screening laboratory came together collaboratively to find the source of the false-positive newborn screening results," Dr. Reindl added. "Without the teamwork displayed at our institution I am doubtful the true cause of the false-positive results would have been discovered."

Dr. Carlos Prada from Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio told Reuters Health, "Newborn screening is a complex test given the variety of metabolites that are measured as surrogate marks of many different conditions. This study is a good example of quality improvement in a hospital based program. The findings help refine the process and to reinforce the need for careful sample and collection given the high sensitivity of mass spectrometers."

Dr. Prada added, "An important conclusion from this study is the need for rapid and proper follow-up of abnormal results of newborn screening accompanied by genetic counseling given the possible scenarios of false positives, true positives, and maternal disease in some cases."

He continued, "It is surprising the significant lack of public awareness about newborn screening in general, and this is also a factor in how families take the news of an abnormal result. This is a reminder of the need for continuous improvement in how we do things at the hospital as well as the impact to society."


 
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