Turnaround times
The quoted turnaround time is from sample receipt in the laboratory, to results authorisation in the Laboratory Information Management system. The times do not include transport of specimen to the laboratory or the administrative process to print and post/email reports. Service users must allow for transport and reporting time when ordering tests.
Clinical background:
Carnitine is required for transport of long-chain fatty acids into the mitochondria for β-oxidation. Primary carnitine deficiency is caused by impaired function of the carnitine transporter protein OCTN2 resulting in renal loss of carnitine, low plasma concentrations and low intracellular carnitine potentially leading to impaired fatty acid oxidation. Measurement of paired urine and plasma free & total carnitine is used in the investigation of primary carnitine deficiency. Calculation of tubular reabsorption of carnitine can determine whether there is increased renal loss of carnitine. Plasma and urine creatinine results are also required for this calculation; these can be measured at NuTH if results are not provided with the request.
Specimen container paediatric:
Plain universal container
Specimen container adult:
Plain universal container
Minimum volume paediatric:
5 mL urine
Minimum volume adult:
3 mL urine
Sample stability:
Free and total carnitine is stable at -20°C for up to 3 months and at -80°C for up to 6 months
Transport requirements:
Samples may be sent by 1st class post to reach the laboratory within 48 hours of collection. On arrival samples should be stored at -20°C or lower if there is a delay in analysis.
Interpretation:
Carnitine is required for the transfer of long-chain fatty acids into mitochondria for b-oxidation. Carnitine also facilitates the removal of excess acyl-CoA esters (i.e. intermediates of fatty acids oxidation, branched-chain amino acid metabolism and drug metabolites) out of the mitochondrial compartment for detoxification and excretion in the urine. Inborn errors of metabolism in which acyl-CoA esters accumulate are associated with increased acylcarnitine concentrations in tissues and blood, and greatly increased urinary excretion of acylcarnitines. The increased excretion of acylcarnitines in the urine is also associated with the excessive loss of free carnitine (inhibition of tubular reabsorption). The chronic loss of free and acylated carnitine into the urine can lead to depletion of tissue stores of L-carnitine and secondary carnitine deficiency. Primary carnitine deficiency is an inborn defect of carnitine uptake into tissues and cells. Patients with this condition have very low levels of tissue and plasma free carnitine and total carnitine. The relative distribution of free carnitine and carnitine esters may vary according to fasting status, renal function, muscular exercise and as a result of a defect of acyl-CoA metabolism. Acylcarnitine fraction tends to increase with fasting or under the conditions of catabolic stress.
Reference ranges:
Free carnitine: 3.0 – 146.0 mmol/mol creatinine
Total carnitine: 12.0 – 294.0 mmol/mol creatinine% Acylated: 20 – 75