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Biochemical investigations in Blood

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Blood Biochemistry
Test Indications Precautions Interpretation
α-AASA Neonatal epileptic seizures (usually with burst-suppression) and any unexplained refractory epilepsy up to the age of 2 years at onset   Supports a diagnosis of pyridoxine-dependent epilepsy (PDE) due to α-AASA-dehydrogenase deficiency
Acylcarnitines Acute metabolic encephalopathy. Acute myopathy, rhabdomyolysis. Unexplained hyperCKaemia   Specific acylcarnitines indicate particular disorders, e.g. octanoyl carnitine in MCAD deficiency, glutaryl carnitine in GA1, propionyl carnitine in cobalamin disorders
Albumin Suspect multisystem disorder (mitochondrial peroxisomal, congenital defect of glycosylation) Discussion with laboratory may be necessary on techniques of albumin estimation ↓ albumin may be the earliest clue to liver involvement in mitochondrial disorders such as with POLG1 mutations
  Part of investigation of CSF in immunological abnormality   Allows calculations of CSF/serum albumin index, IgG albumin ratio and IgG index
Alpha-1 antitrypsin Late neonatal intracranial haemorrhage   ↓ may be alpha-1-antitrypsin deficiency with PiZZ or PiSZ phenotype. ('Clotting screen' abnormal)
Alpha-fetoprotein Ataxic 'cerebral palsy'. Any type of movement disorder in early childhood. 'Oculomotor apraxia' (saccadic impairment)   ↑ in ataxia-telangiectasia, ataxia-oculomotor apraxia 2 (AOA2) and DGUOK deficiency (hepatocerebral form of mtDNA depletion)
Amino acids Learning disability. Hypotonia. Early-onset epileptic seizures including spasms. Acute encephalopathy. Intermittent ataxia. Acquired or progressive dystonia (NB consider BH4deficiency). Arterial ischaemic stroke Deproteinize plasma promptly if homocystinuria is a possibility (see also homocysteine). Negative in homocystinuria after small dose of ingested pyridoxine. Not helpful for serine synthesis defects - need CSF Aminoacidopathies (e.g. PKU, homocystinuria, glycine encephalopathy). Clue to early diagnosis of pyridoxal phosphate-responsive epilepsy and mitochondrial disorders. ↑ alanine may indicate chronic pyruvate accumulation
Ammonia (see also Ischaemic forearm test at end of this chapter) Neonatal seizures ± vomiting. Acute encephalopathy. Vomiting-headache-impaired consciousness complex. 'Stroke'. Intermittent ataxia May be fasting or postprandial or at time of acute illness. Can be venous or arterial but with minimum disturbance. Separate immediately Normal arterial level is higher than venous. ↑ in urea cycle defects. Some organic acidurias. Reye syndrome, sodium valproate therapy, decompensated fatty acid disorders, illness with shock
Bile acids Peroxisomal phenotype -see text   ↑ in various peroxisomopathies
Biotinidase Neurological deterioration ± myelopathy ± skin rash ± alopecia. Remission on biotin trial (see Chapter 2.16) Serum (assay not affected by coincident biotin therapy). Expected organic aciduria may be subtle ↓ in biotinidase deficiency
Ceruloplasmin (copper oxidase) Early seizures, hypotonia, steely hair   ↓ in Menkes disease (unreliable in first weeks)
  Movement and/or behaviour disorder 5 years or older   ↓ in Wilson disease (not always)
Calcium Neonatal seizures. Unexplained seizures ± photophobia, learning disability. Acquired dyskinesia. Basal ganglia calcification   ↓ in hypoealcaemia, true and pseudohypoparathyroidism, DiGeorge syndrome
  Developmental delay ± elfin face   ↑ in diopathic hypercalcaemia, Williams syndrome
Carnitine Acute unexplained encephalopathy. Coma on valproate. Lipid and other acute myopathies   ↓↓ in primary carnitine transport defect. ↓ in various fatty acid oxidation disorders. (Valproate may be associated with carnitine depletion)
Cholestanol Learning disability, juvenile cataracts, limb pains   ↑ in cerebrotendinous xanthomatosis
Cholesterol Developmental delay with retinopathy and sensorineural deafness. Skeletal dysplasias. Ataxia especially with oculomotor apraxia. Spinocerebellar ataxia Fasting ↓ in peroxisomal deficiency, Smith-Lemli-Opitz syndrome and other defects of cholesterol biosynthesis, and abetalipoproteinaemia. ↑ in ataxia-oculomotor apraxia type 1 (A0A1)
Copper Steely hair, early seizures Ensure apparatus is completely copper free and avoid copper contamination ↓ in Menkes disease (unreliable in first weeks)
  Movement disorder ± behaviour disorder age 5 years or over   ↓ in Wilson disease (not always)
CoQ10 Suspect mitochondrial disorder White cells necessary ↑ in ubiquinone deficiency
Creatine kinase Expressive spEEGh delay, toe walking, acquired muscle weakness in a boy. Neonatal and infantile weakness in boys and girls Test with minimal disturbance, preferably not after exercise or biopsy. HyperCKaemia is sometimes unexplained but many causes ↑↑ in Duchenne and Becker muscular dystrophies ± ↑ in manifesting carriers. ↑ in other dystrophies, esp. a-sarcoglycan and caveolin3 (CAV3) mutations. ↑ or ↑↑ in VLCAD, LCHAD, MADD/GA2, CPTII, myophosphorylase and myoadenylate deaminase deficiencies, ryanidine receptor (RYR) mutations and other malignant hyperthermias, usually provoked. ↑ extreme exertion, dyskinesia, low T4, mitochondrial. ↑ in congenital muscular dystrophy (often), myositis (often)
Creatinine Learning disability, epileptic seizures and movement disorder   ± ↓ in GAMT and AGAT deficiency
DHAP-AT Peroxisomal phenotype   ↓ in all cases of reduced peroxisome number
7-dehydrocholesterol Suggestive dysmorphism   ↑ in Smith-Lemli-Opitz syndrome
Electrolytes (sodium/ potassium chloride/ bicarbonate) (Any acute illness.) Paroxysmal weakness   Potassium abnormalities in various periodic paralyses
Endocrine (Cortisol, insulin etc.) Hypoglycaemia, may be epileptic seizures   Low Cortisol may indicate reduced ACTH responsiveness
Ferritin (↓ iron deficiency) 'Seizures'   ↓ neurally mediated syncope
  Unpleasant urge to move legs, relieved by sleep   ↓ restless leg syndrome
  'Infection'   ↑ familial haemophagocytie lymphohistiocytosis
Glucose Reduced consciousness level. Epileptic seizures In fasting test do blood levels immediately before lumbar puncture Various hypoglycaemic situations. Normal blood glucose with ↓ CSF glucose may indicate GLUT1 deficiency
GTP cyclohydrolase-1 (GCH1) Dopa-responsive dystonia and infantile dyskinesia/ parkinsonism with oculogyric crises Estimated in mononuclear cells from peripheral blood -discuss with lab ↓ in Segawa disease and in autosomal recessive GCH1 deficiency
Hexosaminidase A and B (free) Wide neurological phenotype Serum or plasma, ± 'low' in normal children i in Sandhoff disease or juvenile Sandhoff disease
Homocysteine (total plasma homocysteine) Neonatal hypoxic-ischaemic encephalopathy without convincing history More sensitive than urine sulphite test ↑ sulphite oxidase deficiency
Homocysteine (total plasma homocysteine) Arterial ischaemic stroke. 'Psychiatric' myelopathy B<sub<12< sub="> may be normal in genetic cobalamin defects ↑ in homocystinuria, MTHFR deficiency, cobalamin disorders
Lactate (see also Ischaemic forearm test at end of this chapter) Acute encephalopathy (± ↑ anion gap). Suspect mitochondrial disorder. Intermittent ataxia/ movement disorder. Organic aciduria. Hypoglycaemia Minimal disturbance of child (ideally collect sample 30min after placing i.v. catheter) and immediate processing of specimen. May be random or 1h before or 1h after feed ↑ in a wide range of disorders, in particular mitochondrial respiratory chain deficiencies
Lysosomal enzymes Various dysmorphisms, coarse facies, hepatosplenomegaly, developmental regression Know what is being tested for. Beware inferences from 'heterozygous' levels and pseudo-deficiencies. Pay attention to substrate used and note that activator protein deficiency may cause typical disease with normal enzyme levels Specific enzyme deficiency confirms specific targeted diagnosis, e.g. Krabbe disease, metachromatic leukodystrophy, etc.
Magnesium Neonatal seizures   ↓ in disturbances of magnesium metabolism
Manganese Movement disorder, polycythaemia, liver cirrhosis. Brain MRI: manganese in basal ganglia   ↑↑ in novel very rare treatable autosomal recessive disorder
Phosphate Tetany, occasional epileptic seizure. Basal ganglia ± white matter calcification Urine study required when renal tubular function is being tested ↑ in hypoparathyroidism
Phytanic acid Peroxisomal phenotype. Demyelinating neuropathy Diet dependent ↑ in various peroxisomopathies including Refsum disease
Pipecolic acid Neonatal or later onset epilepsy responsive to either pyridoxine (PDE) or pyridoxal phosphate No need to stop pyridoxine treatment ↑ in PDE with a-amino adipic semialdehyde dehydrogenase deficiency
  Peroxisomal-type dysmorphism   ↑ in peroxisomal and related metabolic disorders including GA2
Prolactin Unexplained 'convulsions' Timing important ↑ after both epileptic seizures and syncopes but not after psychological events
Prolactin Investigation of dopamine-related disorders   ↑ in dopamine deficiency disorders
Pyruvate As for blood lactate Preferably 1h after a meal. Unstable: transfer within 30s to 8% perchlorate on ice ↑ in defects of pyruvate dehydrogenase
Thiamine Acquired neurological deficit such as oculomotor impairments and ataxia with bizarre history   Low in Wernicke encephalopathy
Thyroid function tests Typical hypothyroid phenotype   ↓ = hypothyroidism (including in Down syndrome and CDG1a)
  Hashimoto encephalopathy Anti-thyroperoxidase +ve May be euthyroid
  Hereditary chorea   ± ↓ with thyroid transcription factor (TITF-1) mutation
Free T3 (FT3) X-linked learning disability with dystonic 'cerebral palsy' ± eye movement defect ± delayed myelination   ↑ free T3 due to monocarboxylate transporter 8 (MCT8) gene mutation (T4 often ↓)
Transaminases •Congenital infection-like' Negative virology ↑ Aicardi-Goutieres syndrome
  Intractable partial seizures ± myoclonus ± acute encephalopathy   ↑ Alpers (POLG1)
  Incidental finding NB transaminases may come from muscle as well as liver ↑ Muscular dystrophies
  Developmental delay with hypotonia   ↑ in other mitochondrial disorders and CDG
Transferrin (isoelectric focusing for sialotransferrin) Delay, hypotonia, cerebellar hypoplasia/atrophy Choose your laboratory. False negatives for CDG not uncommon especially in neonates and early childhood. False positives in galactosaemia and hereditary fructose intolerance Abnormal in CDG especially type 1a
Urate Early acquired movement disorder with motor delay Urine urate is more reliable (better sensitivity) ↑ in Lesch-Nyhan or similar disorder
Urate Dysequilibrium-diplegia   ↓↓ in purine nucleoside phosphorylase deficiency
  Neonatal epilepsy with cerebral destructive lesions   ↓ in molybdenum cofactor deficiency (is normal in isolated sulphite oxidase deficiency)
Urea Atypical headache often with recurrent impairment of consciousness. 'Stroke'   ↓ plasma urea may indicate urea cycle disorder including heterozygous (OTC) deficiency. ↑ in renal failure and gastrointestinal bleeds, any cause
Very long-chain fatty acids (VLCFAs) Suspect peroxisomopathy Even though D-bifunctional protein (DBP) deficiency affects the VLCFA pathway, DBP deficiency cannot be exluded by normal plasma VLCFA: fibroblast studies needed ↑ in most peroxisomal disorders including all global peroxisomal deficiencies
  School-age regression   ↑ in adrenoleukodystrophy (ALD)
Vitamin A Loss of vision in autism   ↓ with deficient diet
Vitamin B12 Developmental delay in a purely breast-fed infant ± seizures ± movement disorders   ↓ when mother on a vegan (or even a vegetarian) diet. Movement disorder may ↑ after B12 treatment of deficiency. Macrocytosis is not always present
Vitamin E Developmental delay, with retina! defect and sensorineural deafness, spinocerebellar ataxia ± retinitis pigmentosa   ↓ in some peroxisomal disorders, abetalipoproteinaemia, selective vitamin E malabsorption
Abbreviations: CPTII = carnitine palmitoyl transferase II; DHAP-AT = dihydroxyacetone phosphate acyltransferase; LCHAD = long-chain 3-hydroxyacyl-coenzyme A deficiency; MADD/GA2 = multiple acyl-coenzyme A dehydrogenase deficiency/glutaric aciduria type 2; VLCAD = very-long-chain acyl-coenzyme A deficiency.
APA Style
Biochemical investigations in Blood. (n.d.). In ICNApedia. Retrieved August 23,2019 23:36:04 from
MLA Style
"Biochemical investigations in Blood." ICNApedia: The Child Neurology Knowledge Environment, Inc. May 06, 2018. Web. August 23,2019 23:36:04
AMA Style
ICNApedia contributors. Biochemical investigations in Blood. ICNApedia, The Child Neurology Knowledge Environment. May 06, 2018. Available at: August 23,2019 23:36:04.

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