TABLE 1.

Decision Criteria and Confirmatory Analysis for Disorders Detected by Expanded Neonatal Screening With MS/MS

DisorderDecision Criteria for “Positive” Testing in Neonatal Screening Amino Acids or AcylcarnitinesConfirmatory Analyses
(Cutoff, μmol/L)(Cutoff, Molar Ratio)
PKUPhe (>150)Phe/Tyr (>1.7)PKU: Phe >600 μM; non-PKU-HPA: Phe >150 and <600 μM
Tyrosinemia ITyr (>200) and positive succinylacetone test28Succinylacetone in urine, increased α-fetoprotein in serum
Maple syrup urine diseaseLeu(Ile) (>490) and Val (>390)Plasma amino acids and presence of alloisoleucine; enzyme activity in fibroblasts; Classical: Leu 500–5000 μM, BCKD activity <2%; Variant forms: Leu 50–4000 μM, BCKD activity 2–40%
CitrullinemiaCit (>65)Orn/Cit (<1.5) Cit/Arg (>15)Plasma amino acids; enzyme activity in fibroblasts; Classical: Cit ≫ 1000 μM; Variant forms: Cit >50 and <1200 μM, ammonia and arginine normal
Argininosuccinate lyase deficiencyAsa (>1)Enzyme activity in fibroblasts; Asa in urine
Nonketotic hyperglycinemiaGly (>2000)Gly CSF/plasma ratio >0.06
HomocystinuriaMet (>65)Met/Phe (>3) Met/Leu(Ile) (>1)Enzyme activity in fibroblasts; mutational analysis; total homocysteine in plasma ≫20 μM
Long-chain 3-OH acyl-CoA dehydrogenase/mitochondrial trifunctional protein deficiencyC14OH (>0.12) or/and C16:1OH (>0.22) C16OH (>0.20) C18:1OH (>0.12) C18OH (>0.11)Enzyme activity in fibroblasts/lymphocytes
Very long-chain acyl-CoA dehydrogenase deficiencyC14:1 (>0.43) or C14 (>0.76)Enzyme activity in fibroblasts/lymphocytes
MCADC6 (>0.21) or/and C8 (>0.32) C10:1 (>0.28) C10 (>0.48)C8/C2 (>0.02) C8/C10 (>1.6) C8/C12 (>1.6)Enzyme activity in fibroblasts/lymphocytes; mutational analysis; phenylpropionate loading; hexanoyl and suberylglycine in urine; Classical: enzyme residual activity <5% or pathological phenylpropionate loading test or severe mutations; Variant forms: enzyme residual activity 5–35%; negative phenylpropionate loading test; mild mutations
Short-chain acyl-CoA dehydrogenase deficiencyC4 (>2)Enzyme activity in fibroblasts/muscle; mutational analysis; ethylmalonic acid in urine; Classical: ethylmalonic acid in urine and development of clinical symptoms or proven disease causing mutations; Variant forms: ethylmalonic acid in urine and/or decreased enzyme activity, no severe mutations, no clinical symptoms
Multiple acyl-CoA dehydrogenase deficiencyMultiple elevations from C4 to C18Enzyme activities in fibroblasts; lactic, glutaric, and ethylmalonic acid in urine
Carnitine transporter defectC0 (<10) and AC (<5)Carnitine uptake in fibroblasts; mutational analyses; decreased tubular carnitine reabsorption
Carnitine palmitoyltransferase I deficiencyC0 (>90) and C16 (<1.7) C18 (<0.6)C0/(C16 + C18) (>70)Enzyme activity in fibroblasts/lymphocytes
Carnitine palmitoyltransferase II/carnitine-acylcarnitine translocase deficiencyC0 (<10) and C16 (>10.6) C18 (>3.2)C0/(C16 + C18) (<3)Enzyme activity in fibroblasts/lymphocytes
Propionic aciduriaC3 (>6.8)C3/C0 (>0.19) C3/C2 (>0.39)Enzyme activity in fibroblasts; tiglylglycine, 3-hydroxypropionic acid, methylcitrate in urine; ammonia in plasma
Methylmalonic aciduria/ cobalamine disordersC3 (>6.8) or MMA (>1)C3/C0 (>0.19) C3/C2 (>0.39)Enzyme activities in fibroblasts; methylmalonic acid in urine; ammonia and homocysteine in plasma
Glutaric aciduria type IGlut (>0.14)Glut/C8 (>1.8) Glut/C16 (>0.06)Enzyme activity in fibroblasts; glutaric and 3-hydroxyglutaric acid in urine
Isovaleric aciduriaC5 (>2)C5/C2 (>0.06)Enzyme activity in fibroblasts; 3-hydroxyisovaleric acid and isovalerylglycine in urine
HMG-CoA lyase deficiencyC5OH (>1)Enzyme activity in fibroblasts; 3-OH-methylglutaric and 3-methylglutaconic acid in urine
Holocarboxylase synthetase deficiencyC5OH (>1)Enzyme activity in fibroblasts; 3-OH-isovaleric, 3-hydroxypropionic acid, lactate, methylcitrate, and 3-methylcrotonylglycine in urine
3-Methylcrotonyl-CoA carboxylase deficiencyC5OH (>1)Enzyme activity in fibroblasts; 3-OH-isovaleric acid and 3-methylcrotonylglycine in urine; Leu loading test; Classical: diminished enzyme activity or pathological Leu loading test; Variant forms: abnormal organic acids in urine but no increase of C5OH in the mother
  • Phe indicates phenylalanine; Tyr, tyrosine; Leu, leucine; Ile, isoleucine; Val, valine; BCKD, branched-chain α-ketoacid dehydrogenase complex; Cit, citrulline; Orn, ornithine; Arg, arginine; Asa, argininosuccinic acid; Gly, glycine; Met, methionine; C0, free carnitine; C2, acetyl; C3, propionyl; C4, butyryl; C5, isovaleryl; C6, hexanoyl; C5OH, 3-OH-isovaleryl or 2-methyl-3-OH-butyryl; C8, octanoyl; C10:1, decenoyl; C10, decanoyl; MMA, methylmalonyl; Glut, glutaryl; C12, dodecanoyl; C14:1, myristoleyl; C14, myristoyl; C14OH, 3-OH-myristoyl; C16, palmityl; C16:1OH, 3-OH-palmitoleyl; C16OH, 3-OH-palmityl; C18, stearoyl, C18:1OH, 3-OH-oleyl; C18OH, 3-OH-stearoylcarnitine; AC, total acylcarnitines (C3 to C18); HMG, 3-hydroxy-3-methylglutaryl.