Clotted blood tube (Serum gel separator clot activator tube)

Minimum blood volume: 5 mL

Paediatric patient:

Paediatric clotted blood tube

Number of vials: 1

Minimum blood volume: 0.8 mL

Age-related reference intervals provided in patient reports.

(Source: Mayo Clinic Laboratories)

For the differential diagnosis of peroxisomal disorders

Peroxisomes are intracellular organelles that contain enzymes for β-oxidation of very long-chain fatty acids, those with 20 to 26 carbons in length (VLCFA). Therefore, peroxisomal disorders generally manifest with elevated VLCFA levels (except rhizomelic chondrodysplasia). There are 2 types of peroxisomal disorders: those with defective peroxisome formation and those with defects in single peroxisomal enzymes.

Zellweger syndrome (ZS), neonatal adrenoleukodystrophy, and infantile Refsum's disease (IRD):
These are three different phenotypes with decreasing severity from ZS to IRD of a disease continuum. The responsible genetic defect occurs in 1 of at least 11 genes involved in peroxisomal formation or protein import (the PEX gene family). Clinical presentations may include facial dysmorphism, CNS malformations, demyelination, neonatal seizures, hypotonia, hepatomegaly, cystic kidneys, short limbs with stippled epiphyses (chondrodysplasia punctata), cataracts, retinopathy, hearing deficit, psychomotor delay, and peripheral neuropathy. Diagnosis is by demonstrating elevated blood levels of VLCFA, phytanic acid, bile acid intermediates, and pipecolic acid.

Rhizomelic chondrodysplasia punctata:
This defect of peroxisomal biogenesis is caused by PEX7 gene mutations and characterised by skeletal changes that include midface hypoplasia, strikingly short proximal limbs, frontal bossing, small nares, cataracts, ichthyosis, and profound psychomotor retardation. Vertebral clefts are also common. Diagnosis is by x-ray findings, serum elevation of phytanic acid, and low RBC plasmalogen levels; VLCFA levels are normal.

X-linked adrenoleukodystrophy:
This disorder is caused by deficiency of the peroxisomal membrane transporter ALDP, coded for by the gene ABCD1. The cerebral form affects 40% of patients. Onset occurs between age 4 and 8 year, and symptoms of attention deficit progress over time to severe behavioral problems; dementia; and vision, hearing, and motor deficits, causing total disability and death 2 to 3 year after diagnosis. Milder adolescent and adult forms have also been described. About 45% of patients have a milder form called adrenomyeloneuropathy (AMN); onset occurs in the 20s or 30s, with progressive paraparesis, and sphincter and sexual disturbance. About 1/3 of these patients also develop cerebral symptoms. Patients with any form may also develop adrenal insufficiency; about 15% have isolated Addison's disease without neurologic involvement. Diagnosis is confirmed by isolated elevation of VLCFA.

Classic Refsum's disease:
The disease is caused by deficiency of phytanoyl-CoA hydroxylase, which catalyses metabolism of phytanic acid (a common dietary plant component). Clinical presentation may include progressive peripheral neuropathy, impaired vision from retinitis pigmentosa, hearing deficit, anosmia, cardiomyopathy and conduction defects, and ichthyosis. Onset is usually in the 20s. Diagnosis is confirmed by elevation of serum phytanic acid and decreased levels of pristanic acid (phytanic acid elevation is accompanied by pristanic acid elevation in several other peroxisomal disorders).