Dried Urine Spots for Quantification of C0 (Free) Carnitine Excretion: A Validated Method for Follow-Up and Confirmatory Testing of Primary Carnitine Deficiency.
4 affiliations
- 1Section Metabolic Diagnostics, Department of Genetics, University Medical Center Utrecht, 3584 EA Utrecht, The Netherlands.
- 2Laboratory Genetic Metabolic Diseases, Department of Laboratory Medicine, Amsterdam UMC, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
- 3Department of Endocrinology and Metabolism, Amsterdam Gastroenterology Endocrinology Metabolism (AGEM) Research Institute, Amsterdam University Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
- 4Department of Metabolic Diseases, Wilhelmina Children's Hospital, University Medical Center Utrecht, 3584 EA Utrecht, The Netherlands.
Abstract
Primary carnitine deficiency (PCD), caused by Organic Cation Transporter Novel 2 (OCTN2) deficiency, is detected by newborn screening (NBS) through low blood free carnitine (C0) concentrations. Confirmation of the diagnosis may be supported by demonstrating increased urinary C0 excretion, but urine collection in newborns is technically challenging. We developed and validated a dried urine spot (DUS) method for quantifying urinary C0 excretion as a practical, non-invasive alternative to conventional liquid urine sampling. This approach has the potential to allow parents to obtain urine at home by placing filter paper cards between the baby's skin and a dry diaper, simplifying sample collection. C0 carnitine and creatinine were quantified in 6 mm DUS punches by flow injection analysis-tandem mass spectrometry (FIA-MS/MS) following butylation. The method was analytically validated for sensitivity, precision, stability, and agreement with liquid urine measurements. The method demonstrated excellent analytical performance, with lower limits of detection (LLOD)/lower limits of quantification (LLOQ) values of 0.02/0.07 µmol/L for C0 and 0.01/0.04 mmol/L for creatinine. Normalization of C0 to creatinine reduced variability related to sampling and punch location. Both analytes remained stable in DUS for at least 10 days at room temperature and after 11 freeze-thaw cycles. C0/creatinine obtained from DUS showed excellent agreement with liquid urine (R² > 0.9967), although concentrations were consistently lower, requiring a correction factor of 1.27 to estimate concentrations equivalent to liquid urine. DUS provides a reliable and accurate alternative to liquid urine for measuring C0 excretion in newborns. This simple, home-based sampling approach facilitates non-invasive urine collection and has the potential to support follow-up and confirmatory testing of PCD.
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BibTeX
@article{ham2026dried,
title = {{Dried Urine Spots for Quantification of C0 (Free) Carnitine Excretion: A Validated Method for Follow-Up and Confirmatory Testing of Primary Carnitine Deficiency.}},
author = {Maria van der Ham and Sacha Ferdinandusse and Mirjam Langeveld and Sabine A Fuchs and Monique G M de Sain van der Velden and On Behalf Of The Odin Study Group},
journal = {International journal of neonatal screening},
year = {2026},
month = oct,
doi = {10.3390/ijns12040084},
url = {https://europepmc.org/article/MED/42924761},
note = {CC BY},
}
RIS
TY - JOUR
TI - Dried Urine Spots for Quantification of C0 (Free) Carnitine Excretion: A Validated Method for Follow-Up and Confirmatory Testing of Primary Carnitine Deficiency.
AU - Maria van der Ham
AU - Sacha Ferdinandusse
AU - Mirjam Langeveld
AU - Sabine A Fuchs
AU - Monique G M de Sain van der Velden
AU - On Behalf Of The Odin Study Group
PY - 2026
DA - 2026/10/12
JO - International journal of neonatal screening
DO - 10.3390/ijns12040084
UR - https://europepmc.org/article/MED/42924761
AB - Primary carnitine deficiency (PCD), caused by Organic Cation Transporter Novel 2 (OCTN2) deficiency, is detected by newborn screening (NBS) through low blood free carnitine (C0) concentrations. Confirmation of the diagnosis may be supported by demonstrating increased urinary C0 excretion, but urine collection in newborns is technically challenging. We developed and validated a dried urine spot (DUS) method for quantifying urinary C0 excretion as a practical, non-invasive alternative to conventional liquid urine sampling. This approach has the potential to allow parents to obtain urine at home by placing filter paper cards between the baby's skin and a dry diaper, simplifying sample collection. C0 carnitine and creatinine were quantified in 6 mm DUS punches by flow injection analysis-tandem mass spectrometry (FIA-MS/MS) following butylation. The method was analytically validated for sensitivity, precision, stability, and agreement with liquid urine measurements. The method demonstrated excellent analytical performance, with lower limits of detection (LLOD)/lower limits of quantification (LLOQ) values of 0.02/0.07 µmol/L for C0 and 0.01/0.04 mmol/L for creatinine. Normalization of C0 to creatinine reduced variability related to sampling and punch location. Both analytes remained stable in DUS for at least 10 days at room temperature and after 11 freeze-thaw cycles. C0/creatinine obtained from DUS showed excellent agreement with liquid urine (R² > 0.9967), although concentrations were consistently lower, requiring a correction factor of 1.27 to estimate concentrations equivalent to liquid urine. DUS provides a reliable and accurate alternative to liquid urine for measuring C0 excretion in newborns. This simple, home-based sampling approach facilitates non-invasive urine collection and has the potential to support follow-up and confirmatory testing of PCD.
SN - 2409-515X
ER -