title: Differences between acylcarnitine profiles in plasma and bloodspots.
abstract: Quantification of acylcarnitines is used for screening and diagnosis of inborn error of metabolism (IEM). While newborn screening is performed in dried blood spots (DBSs), general metabolic investigation is often performed in plasma. Information on the correlation between plasma and DBS acylcarnitine profiles is scarce. In this study, we directly compared acylcarnitine concentrations measured in DBS with those in the corresponding plasma sample. Additionally, we tested whether ratios of acylcarnitines in both matrices are helpful for diagnostic purpose when primary markers fail.
  
  
  METHODS
  DBS and plasma were obtained from controls and patients with a known IEM. (Acyl)carnitines were converted to their corresponding butyl esters and analyzed using HPLC/MS/MS.
  
  
  RESULTS
  Free carnitine concentrations were 36% higher in plasma compared to DBS. In contrast, in patients with carnitine palmitoyltransferase 1 (CPT-1) deficiency free carnitine concentration in DBS was 4 times the concentration measured in plasma. In carnitine palmitoyltransferase 2 (CPT-2) deficiency, primary diagnostic markers were abnormal in plasma but could also be normal in DBS. The calculated ratios for CPT-1 (C0/(C16+C18)) and CPT-2 ((C16+C18:1)/C2) revealed abnormal values in plasma. However, normal ratios were found in DBS of two (out of five) samples obtained from patients diagnosed with CPT-2.
  
  
  CONCLUSIONS
  Relying on primary acylcarnitine markers, CPT-1 deficiency can be missed when analysis is performed in plasma, whereas CPT-2 deficiency can be missed when analysis is performed in DBS. Ratios of the primary markers to other acylcarnitines restore diagnostic recognition completely for CPT-1 and CPT-2 in plasma, while CPT-2 can still be missed in DBS.
authors: Department of Medical Genetics, UMC Utrecht, The Netherlands Wilhelmina Children's Hospital, University Medical Centre (UMC) Utrecht, Utrecht, The Netherlands. m.g.desain@umcutrecht.nl
authors: Monique G M
authors: MG
authors: de Sain-van der Velden
authors: Eugene F
authors: EF
authors: Diekman
authors: Judith J
authors: JJ
authors: Jans
authors: Maria
authors: M
authors: van der Ham
authors: Berthil H C M T
authors: BH
authors: Prinsen
authors: Gepke
authors: G
authors: Visser
authors: Nanda M
authors: NM
authors: Verhoeven-Duif
mesh_terms: D002331:Carnitine / Q000031:analogs & derivatives* / Q000097:blood; D002334:Carnitine O-Palmitoyltransferase / Q000097:blood* / Q000172:deficiency*; D059788:Dried Blood Spot Testing; D006801:Humans; D007003:Hypoglycemia / Q000097:blood*; D007231:Infant, Newborn; D008052:Lipid Metabolism, Inborn Errors / Q000097:blood*; D008661:Metabolism, Inborn Errors / Q000097:blood / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology; D015997:Neonatal Screening; D011237:Predictive Value of Tests
chemical_list: C116917:acylcarnitine; D002334:Carnitine O-Palmitoyltransferase; D002331:Carnitine
keywords: Acylcarnitines; CPT-1; CPT-2; DBSs; Dried blood spot; Fatty acid oxidation disorders; GA-I; IEM; LCHAD; MCAD; MMA; Organic acidurias; PA; Ratios; VLCAD; carnitine palmitoyltransferase 1; carnitine palmitoyltransferase 2; dried blood spots; glutaric acidemia I; inborn error of metabolism; long-chain 3-hydroxyacyl-CoA dehydrogenase; medium-chain acyl-CoA dehydrogenase; methylmalonic acidemia; propionic acidemia; very-long-chain acyl-CoA dehydrogenase; β-ketothiolase; βKT