EDTA in dried blood spots leads to false results in neonatal endocrinologic screening.
BACKGROUND
Blood samples for neonatal screening for inborn errors of metabolism are collected and shipped on standardized filter paper cards. Occasionally these samples are contaminated with EDTA, which is often used for anticoagulation. EDTA may interfere with newborn screening tests based on lanthanide fluorescence and thus lead to false-negative or false-positive results.


METHODS
We used tandem mass spectrometry (MS/MS) to detect EDTA in dried blood spots by use of an extra experiment that was integrated into the standard MS/MS neonatal screening and did not require an additional sample spot, nor extra time or work. We analyzed the influence of different blood sampling procedures on lanthanide fluorescence tests for thyroid-stimulating hormone (TSH) and 17-hydroxyprogesterone (17-OHP).


RESULTS
EDTA was increased in 138 of 190 000 newborn screening samples, 27 of which caused false- positive results in the immunoassay for 17-OHP. No false-negative TSH results were found. False-positive results in the 17-OHP test occurred when EDTA concentrations were >2.0 g/L; the TSH test, however, produced false negatives only when EDTA concentrations were >3.0 g/L. Using EDTA-containing devices the procedure of blood collection significantly influenced the concentration of the anticoagulant.


CONCLUSIONS
Addition of EDTA quantification into standard MS/MS tests is a simple and useful method to avoid false-positive or false-negative neonatal screening results in lanthanide fluorescence-based tests.
Holtkamp
Ute
U
Screening-Labor Hannover, Hannover, Germany.
Klein
Jeanette
J
Sander
Johannes
J
Peter
Michael
M
Janzen
Nils
N
Steuerwald
Ulrike
U
Blankenstein
Oliver
O
D001800:Blood Specimen Collection; D002614:Chelating Agents / Q000032:analysis*; D004492:Edetic Acid / Q000097:blood*; D005188:False Negative Reactions; D005189:False Positive Reactions; D006801:Humans; D007231:Infant, Newborn; D015997:Neonatal Screening / Q000379:methods*; D053719:Tandem Mass Spectrometry
D002614:Chelating Agents; D004492:Edetic Acid