Organic Acid Disorders
Urgent investigations – organic acid and amino acid disorders
Patients with suspected amino acid or organic acid disorders may require urgent studies in order to implement appropriate treatment. These patients often present in the neonatal period with failure to thrive, vomiting, lethargy, hyperventilation, seizures and hypotonia. There may be metabolic acidosis, respiratory alkalosis, hypoglycaemia, hypocalcaemia and/or deranged liver function tests. Blood ammonia and lactate may be raised.
For organic and amino acid screen, as well as acylcarnitines, please send 10ml fresh urine and 2ml heparinised blood or a blood card with 4 spots of blood. Results should be available the same day assuming samples arrive in good time (before 11am) and the laboratory has been warned of the urgent sample. It is important that full clinical details are given including details of metabolic acidosis, jaundice, blood ammonia and drug history. For disorders of fat oxidation e.g. MCAD deficiency, it is important that urine is collected at the time of hypoglycaemic stress. Urgent investigations will normally only be performed following discussions with one of our consultants.
| Test | Required specimen & volume | Special precautions | Turnaround time | Reference ranges | Section |
|---|---|---|---|---|---|
| Organic acids by GC-MS* | 5ml plain U | Full drug history | 3 working weeks | Qualitative | Metabolites |
| Pyruvate carboxylase | CC, AFC, CCV, CVS | Contact lab prior to dispatch to discuss test. | Dependent on culture time | Fibroblasts 6 – 40 nmol/h/mg | Metabolites |
| Methylmalonic acid quantitation in plasma | 2ml EDTA or HEP | Contact lab prior to dispatch test | 4 working weeks | Quoted on report | Metabolites |
| Methylmalonic acid quantitation in urine | 2 ml Plain U | Contact lab prior to dispatch test | 4 working weeks | Quoted on report | Metabolites |
|
Succinylacetone — Qualitative screen on DBS Tyrosinaemia Type I |
DBS |
Contact lab prior to sampling; sample must reach lab within 24 hours. |
4 working weeks | Absent in normal subjects | Metabolites |
|
Propionyl-CoA carboxylase Propionic aciduria |
CC, AFC, CCV, CVS | Contact lab prior to dispatch to discuss test | Dependent on culture time | 40 – 100 nmol/h/mg (fibroblasts) | Metabolites |
|
Methylmalonic-CoA mutase Methylmalonic aciduria |
CC, AFC, CCV, CVS | Contact lab prior to dispatch to discuss test | Dependent on culture time | Fibroblasts 207 – 1730 pmol/min/mg | Metabolites |
|
14C-propionate incorporation Propionic and Methylmalonic aciduria defects in B12 Metabolism |
CC, AFC, CCV, CVS | Contact lab prior to dispatch to discuss test | Dependent on culture time | Assay Controls quoted | Metabolites |
| Methylcrotonyl-CoA carboxylase | CC, AFC, CCV | Contact lab prior to dispatch to discuss test | Dependent on culture time | 2.5 – 12 nmol/h/mg (fibroblasts) | Metabolites |
|
HMG-CoA lyase 3-hydroxy 3-methylglutaric aciduria |
CC, AFC, CCV | Contact laboratory prior to dispatch to discuss test | Dependent on culture time | 0.52 – 3.96 nmol/min/mg protein | Metabolites |
|
Biotinidase Multiple carboxylase deficiency |
2 – 3ml HEP, or P | To reach lab within 24 hours | 2 working weeks | Plasma 4 – 12nmol/min/ml | Metabolites |
| Acyl carnitines (Includes free carnitine) | 1ml HEP or EDTA or DBS | None | 2 working weeks |
Free carnitine 20 – 40µM, values quoted for specific acyl carnitines |
Metabolites |
* All samples must be accompanied by relevant clinical details. This is particularly imperative for urine amino acids, urine organic acids, urine mucopolysaccharides and all samples for prenatal diagnosis. Reports may be withheld where samples are received without clinical details as an accurate interpretation may not be possible without them.