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Biochemical investigations in Urine

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Urine biochemistry
Test Indications Precautions Interpretation
α-AASA (a-amino-adipic semialdehyde) Neonatal epileptic seizures (usually with suppression-burst), or later pyridoxine-responsive epilepsy No need to obtain urine before giving pyridoxine or pyridoxal phosphate. May be only slightly raised. Do pipecolic acid also in plasma Pyridoxine-dependent epilepsy (PDE) due to α-AASA-dehydrogenase deficiency (see also Clinical Vignette 2.16.1)
Acylcamitines (plasma more useful) Acute metabolic encephalopathy (plasma better) Excretion ↑↑ by carnitine load (100mg/kg) except when enzyme defect confined to brain. May be difficult to interpret Specific acylcarnitines indicate particular disorders, e.g. octanoyl carnitine in MCAD deficiency, glutaryl carnitine in glutaric acidura type 1 (GA1)
Amino acids Learning disability, acute encephalopathy, intermittent ataxia, various syndromes including Lowe 24-h sample not necessary. If unusual amino acid being sought (e.g. S-sulphocysteine in sulphite oxidase deficiency) discuss with laboratory Relate to dietary input. Significance of minor deviations from 'normal' uncertain. Abnormalities in amino-acidopathy, organic acidaemias, sulphite oxidase deficiency, renal tubular leak (including mitochondrial disorders, Wilson disease). 'False' aminoaciduria in GAMT deficiency
Bile acids Suspect peroxisomopathy Arrange with reference laboratory in advance. Random sample -freeze immediately Abnormal bile acids excreted in many peroxisomal disorders (especially single enzyme defects as D-bifunctional protein deficiency). Output declines with age so ± negative after early infancy
Copper Acquired movement disorder, acquired behaviour disorder ± abnormal liver function 24-h urine. Meticulous attention to ensure copper-free containers and to prevent copper contamination Elevation = Wilson disease (false negative in 5%)
Creatine/creatinine ratio Boys with learning disability False positives possible if diet high in creatine (meat, oily fish) ↑ in creatine transporter deficiency
6AG (glycosaminoglycans, mucopolysaccharides - see also Oligosaccharides) Learning disability ± coarse features, corneal clouding, dysostosis. SpEEGh deterioration. Behavioural difficulties, especially aggression in Sanfilippo disease 24-h collection for heparan sulphate if Sanfilippo likely and initial test for GAG is negative (and specific gene mutation analysis is not possible) Mucopolysaccharidoses will be detected, especially heparan sulphate in Sanfilippo disease. Excess possible in Lowe and Zellweger syndromes and in peroxisomopathies. False increase in GAMT deficiency
  Regression at any age Wise to check leukocyte beta-galactosidase Keratan sulphate + increased in all forms of GM1 gangliosidosis
Guanidinoacetate (GAA) Language delay, early epilepsy, movement disorder H-MRS for creatine peak desirable ↑ in GAMT deficiency. ↓1 in AGAT deficiency
VMA (HMMA). HVA (catecholamines) Acute or subacute cerebellar ataxia/myoc onus/opsoclonus Special diet no longer usually indicated; 24-h urine preferred (whole body imaging more reliable) Increase is consistent with occult neuroblastoma, but result is commonly normal when opsoclonus/myoclonus or other movement disorder is caused by neural crest tumour
VMA (HMMA), HVA (catecholamines) Early dystonia with oculogyric crises Avoid levodopa beforehand ↓ in sepiapterin reductase deficiency
  Neonatal hypothermia/failure to thrive Hair may be normal ↑ HVA/VMA ratio in Menkes disease (>4.0)
Myoglobin Toddler-age encephalopathy with elevatec creatine kinase Random sample Rhabdomyolysis primary or secondary. Too many causes to list but include carnitine transport defects, fatty acid disorder that will need organic acid analysis and acylcarnitines and possibly muscle biopsy for diagnosis
Oligosaccharides Learning disability ± coarse features, corneal clouding, dysostosis. May be dysmorphic neonate, hydrops. Myoclonus epilepsy Random sample adequate Mucclipidoses detected in particular
Organic acids (easily recognizable organic acidaemias are not discussed) Developmental delay, learning disability, "cerebral palsy', macrocephaly, dystonia, chorea, encephalopathy (± epileptic seizures), regression, myelopathy. Rarely of value in 'pure' epilepsy Freeze urine immediately. Test during acute illness in a condition with episodes of encephalopathy (such as GA1). False positive with medium-chain triglyceride oil. False 1 in GAMT deficiency Specific patterns of acids may suggest diagroses: glutaric (GA1); glutaric, ethylmalonic, adipic (GA2); L-2-hydroxyglutaric(L-2-hydroxyglutaric aciduria); N-acetylaspartic (Canavan disease); 4-hydroxybutyric (SSADH deficiency); methylmalonic (cobalamin disorders)
Orotic acid III neonate.. Vomiting-headache-impaired consciousness complex. 'Stroke'. ↓ ammonia Random sample. Interpretation should be by metabolic expert If ↑= ornithine transearbamylase deficiency, hyperornithinaemia-hyperammonaemia-homocitrullinuria (HHH) syndrome, and other rare pyrimidine synthesis defects. If in doubt, repeat after protein load under expert supervision
Oxalic acid Dysmorphism, developmental delay, hypotonia Add HCI as preservative Peroxisomopathies
Phosphate 5uspected mitochondrial disorder Plasma phosphate necessary for formula Reduced phosphate reabsorption = tubular dysfunction
Porphyrins Acquired motor neuropathy ± convulsive seizures ± abdominal colic (at puberty) Random sample, then 24-h urine Excess excretion leads to specific tests for acute intermittent porphyria
Pteridines Delay, seizures, dystonia ± fluctuation Phenylalanine may be only mildly ↑ in plasma Biopterin % of pterins: ↓ biopterin synthesis defects (most commonly PTPS deficiency). ↑ DHPR deficiency
Sialic acid (free) Features of infantile free sialic acid storage disease (see literature for further details) Single urine. Screen for oligosaccharides will not detect free sialic acid All patients show vacuolated lymphocytes. 10- to 20-fold increase in sialic acid storage disease. 100-fold increase in sialuria
Succinyl purines (Bratton-Marshall trst) Neonatal seizures, delay, autism, Angelman-like, + dysmorphism Freeze random morning urine; purine reference laboratory will confirm ↑ in adenylosuccinate lyase deficiency. ↓ in AICA (5-amino-4-imidazolecarboxamide) ribosiduria
Sulphatides Suspect metachromatic leukodystropy (MLD) Urinary sediment. Important to test if arylsulphatase A (ARSA) low in case pseudodeficiency ↑ in all cases of MLD including those with normal ARSA but activator protein (saposin-B) deficiency
Sulphite Neonatal encephalopathy Stix test must be done immediately on freshly passed urine. Bag urine not suitable. Repeat as often as necessary if diagnosis strongly suspected (but may be true negatives) May be positive in molybdenum cofactor deficiency or sulphite oxidase deficiency. Quantatitive determination of sulphite by anion column chromatography is necessary
Uracil Childhood encephalopathy Blood ammonia ± urine orotic acid may be normal ↑ in late-onset ornithine transcarbamylase (OTC) deficiency
Urate Early seizures ± opisthotonus. Early acquired movement disorder with motor delay and high or high-normal plasma urate. Ataxic cerebral palsy ('dysequilibrium-diplegia') 24h urine preferable. Urine urate is more sensitive than plasma urate estimation ↑ output = Lesch-Nyhan syndrome or similar disorder. ↓ excretion = deficiency of molybdenum cofactor or purine nucleoside phosphorylase

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