Vii. Urine Screening for Metabolic Disorders

Denielle Genesis B. Camato

VII. URINE SCREENING FOR METABOLIC DISORDERS ANALYSIS OF URINALYSIS AND BODY FLUIDS | REVIEWER

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OVERFLOW VERSUS RENAL DISORDERS

TWO CATEGORIES IN RENAL DISORDERS

a) OVERFLOW TYPE Ô Results from the disruption of a normal metabolic pathway

that causes increased plasma concentrations of non-metabolized substances.

b) RENAL TYPE

Ô caused by malfunctions in the tubular reabsorption mechanism (see Chap 8; Tubular Disorders)

E Metabol ic Disturbances- most encountered abnormalities that

produce urinary overflow of substances involved in CHON and CHO metabolism

E Inborn Error of Metabol ism- disruption of enzyme function can be caused by failure to inherit the gene to produce a particular enzyme, or by organ malfunction from disease or toxic reactions.

ABNORMAL METABOLIC CONSTITUENTS FOR CONDITIONS DETECTED IN THE ROUTINE URINALYSIS

MAJOR DISORDERS OF PROTEIN & CARBOHYDRATE METABOLISM ASSOCIATED WITH ABNORMAL URINARY CONSTITUENTS CLASSIFIED AS TO FUNCTIONAL DEFECT

AMINO ACID DISORDERS

R Phenylketonuria (PKU) R Tyrosinuria R Alkaptonuria R Melanuria R Maple syrup urine disease R Organic acidemias R Indicanuria R Cystinuria R Cystinosis

PHENYLALANINE – TYROSINE DISORDERS

Ô Metabolic defects cause production of excessive amounts of melanin.

PHENYLKETONURIA

Ô Most well-known of the aminoacidurias; may lead to mental retardation if remain undetected

Ô first identified in NORWAY by Ivan Folling, 1934 Ô Mousy-odor to urine Ô Increased amts of keto-acids including phenylpyruvate Ô Decrease production of tyrosine and its pigmentation

metabolite, melanin Ô Failure to inherit gene, phenyalanine hydroxylase Ô PHENYLALANINE, major constituent of milk from infants

diet

¶ GUTHRIE TEST, most well-known test for PKU ¶ Blood from heelstick is absorbed into filter paper; blood

impregnated disks are then placed on culture media streaked with Bacillus subtilis

¶ Beta-2-thienylalanine, inhibitor of B. subtilis ¶ Tube test based on ferric chloride reaction; addition of ferric

chloride to urine with phenylpyruvic acid produces permanent blue-green color

TYROSYLURIA

Ô Accumulation of excess tyrosine in the plasma (tyrosinemia) Ô Urine may contain excess tyrosine or its degradation

products p-hydroxyphenylpyruvic acid & p-hydroxyphenyllactic acid

Ô most frequently seen is a transitory tyrosinemia in premature infants; under development of the liver function

Ô Reaction can be distinguished from the PKU reaction in the ferric chloride tube test because green color fades rapidly when tyrosine is present

Ô Nitroso-naphthol test, recommended urinary screening test, orange-red is positive color

ALKAPTONURIA

Ô Observed form urine of patients that has darkened urine after becoming alkaline from standing at room temperature; described by GARROD (1902)

Ô ‘alkali lover’ or alkaptonuria term adopted Ô Failure to inherit the gene to produce the enzyme

homogentisic acid oxidase Ô Brown-stained or black-stained cloth diapers; in later life

brown pigment becomes deposited in body tissues (particularly in ears)

Ô Ferric chloride test� blue color Ô Benedicts test/ Clinitest � yellow color (indicating presence

of reducing substance) Ô More specific screening test for urinary homogentisic acid is

to add alkali to freshly voided urine to observe darkening of the color

Ô Addition of silver nitrate and ammonium hydroxide will also produced black urine



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SEROTONIN molecular structure

MELANURIA

Ô MELANIN- the pigment responsible for the dark color of hair, skin, and eyes. Deficient production of melanin results in albinism

Ô Increased urinary melanin will produced darkening of urine (just like homegentisic acid); elevation of urine melanin is a serious finding that indicates the overproliferation of the normal melanin-producing cells (melanocytes) producing malignant melanin.

Ô 5,6-dihydroxyindole- colorless precursor of melanin Ô Ferric chloride test � gray or black precipitate Ô Sodium nitroprusside test � red color Ô Intereference sources: Acetone & Creatinine; to avoid,

just add glacial acetic acid w/c will cause melanin to revert to a green-black color whereas acetone turns purple and Creatinine becomes amber.

BRANCHED-CHAIN AMINO ACID DISORDERS

Ô The branched-chain amino acids differ from other amino acids by having a methyl group that branch from the main aliphatic carbon chain.

2 GROUPS:

¶ Accumulation of one or more of the early amino acid degradation products g eg: Maple Syrup Urine Disease

¶ Disorders in the other group are termed organic acidemias and result in accumulation of organic acids produced further down in the amino acid metabolic pathway

MAPLE-SYRUP URINE DISEASE

Ô Cause by an inborn error of metabolism, inherited as an autosomal recessive trait.

Ô Amino acids involve: leucine, isoleucine, & valine Ô Three amino acids in liver (∞-ketoisovaleric, ∞-

ketoisocaproic, & ∞-keto-β-methylvaleric). Failure to inherit the gene for the enzyme necessary to produce oxidative decarboxylation of these keto acids results in their accumulation in blood and urine.

Ô Urine produces strong odor resembling maple syrup, which is caused by the rapid accumulation of keto acids in urine

Ô 2,4-dinitrophenylhydrazine (DNPH)- screening test most frequent performed for keto acids � yellow turbidity or precipitate

Ô Interference: large dose of ampici l l in

ORGANIC ACIDEMIAS

TRYPTOPHAN DISORDERS

Ô The major concern of the urinalysis laboratory in the metabolism of tryptophan is the increased urinary excretion of the metabolites indicant and 5-hydroxylindoleacetic acid (5-HIAA)

INDICANURIA

Ô Tryptophan usually enters the body to be reabsorbed for use of the body in the production of protein or is converted to indole by the intestinal bacteria & excreted in the feces; however if there are intestinal disorders (eg: obstruction, Hartnup disease, etc) increases amount of tryptophan are converted to indole.

Ô Hartnup disease g blue staining of infants diapers refer to as “blue-diaper syndrome”

Ô Ferric chloride g deep blue or violet color; can subsequently be extracted into chloroform

5-HYDROXYINDOLEACETIC ACID (5-HIAA)

Ô SEROTONIN- used for the stimulation of smooth muscles; produced from tryptophan by the argentaffin cells in the intestine and is carried through the body primarily by the platelets; major constituent of foods: bananas, pineapples, tomatoes

Ô When carcinoid tumors involving the argentaffin (enterochromaffin) cells develop, excess amounts of serotonin are produced, resulting in the elevation of urinary 5-HIAA levels

Ô Nitrous acid + 1-nitroso-2-naphthol g urine with 5-HIAA = purple to black color

Ô Normal dai ly excretion of 5-HIAA: 2-8 mg (argentaffin cells tumors will produce from 160 to 628 mg/24 hours)

Ô Specimen: Random or First morning urine

Ô Specimen: if 24 hour urine g preserved with HCL or Boric Acid

Ô Interference: Phenothiazines and Acetanilids



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CYSTINE DISORDERS

Ô CYSTINURIA- defect in the renal tubular transport of amino acids

Ô CYSTINOSIS- inborn error of metabolism Ô A noticeable odor of sulfur may be present in the urine in

disorders of cystine metabolism

CYSTINURIA

Ô Marked by elevated amounts of the amino acid cysteine in the urine

Ô Inability of the renal tubules to reabsorbed cysteine filtered by the glomerulus

Ô 2 MODES: R Reabsorption of all four amino acids (cysteine,

lysine, arginine, & ornithine) R The other in which only cysteine & lysine are not

reabsorbed Ô 65% of these people can be expected to produce calculi

early in life Ô Cyanide-Nitroprusside- chemical screening test � red-

purple color Ô False Positives: presence of Ketones & homocystine

CYSTINOSIS

Ô Regarded as genuine inborn error of metabolism Ô Incomplete metabolism of cystine results in crystalline

deposits of cysteine in many areas of the body, including the cornea, bone marrow, lymph nodes, and internal organs

Ô FANCONIS SYNDROME- major defect in the renal tubular reabsorption mechanism

Ô Urinalysis: Polyuria, Aminoaciduria, (+) test for reducing substances, lack of urinary concentration

Ô Progression to total renal failure Ô Renal transplants & use of cystine-depleting medications to

prevent cysteine build up in other tissues are extending lives

HOMOCYSTINURIA

Ô Increased urinary homocystine gives a positive result with the cyanide-nitroprusside test

Ô Positive cyanide-nitroprusside test result must be followed by si lver-nitroprusside test in which only homocystine will react

Ô The use of silver nitrate in place of sodium cyanide will reduce homocystine to its nitroprusside reactive-form but will not reduce cysteine.

Ô Positive reaction in the silver-nitroprusside test confirms the presence of homocytinuria

Ô Specimen: Fresh Urine

PHORPHYRIN DISORDERS

Ô Porphyrins are the intermediate compunds in the production of heme

Ô Three primary porphyrins: (uroporphyrin, coproporphyrin, protoporphyrin)

Ô Porphyrin precursors: (∞-aminolevul in ic acid [ALA] & porphobil inogen)

Ô ALA, porphobilinogen & uroporphyrin are the most soluble & readily appear in the urine.

Ô Coporphyrin is less soluble but is found in the urine Ô Protoporphyrin is not seen in urine Ô Fecal Analysis usually performed for detection of

coproporphyrin & protoporphyrin; however to avoid false positive BILE is more acceptable specimen.

Ô FREE ERYTHROCYTE PORPHYRIN (FEP)- analysis of whole blood recommended by Centers for Disease Control (CDC) as screening test for lead poisoning

Ô PORPHYRIAS- disorders of porphyrin metabolism; can be inherited or acquired from erythrocytic& hepatic malfunctions or exposure to toxic agents

Ô Port-wine/Red color to the urine Ô Congenital Porphyria is sometimes suspected from a red

discoloration of an infants diapers Ô ERHLICHS Reaction & Fluorescence under ultraviolet

light in 550 to 600nm are two screening tests for porphyrinuria

Ô ERHLICHS g detection of ALA & Porphobilinogen only Ô Acetylacetone g added to specimen to convert ALA to

porphobilinogen prior to performing Ehrlich test Ô FLUORESCENT TECHNIQUE g used for other porphyrins Ô Ehrl ich Test & Watson-Schwartz test & Hoesch test-

for differentiation between presence of urobilinogen & porphobilinogen

MUCOPOLYSACCHARIDE DISORDERS

Ô Glycosaminoglycans; group of large compunds located primarily in the connective tissue.

Ô Products most frequently found in urine are dermatan sulfate, keratin sulphate, heparin sulphate

Ô Hurler’s Syndrome, Hunter’s Syndrome, San Filipippo’s Syndrome- best known disorders of mucopolysaccharides

Ô Hurler & Hunter g skeletal structure are abnormal & there is severe mental retardation; in Hurler’s syndrome mucopolysaccharides accumulate in the cornea of the eye.

Ô San Filippo’s syndrome g only abnormality is mental retardation

Ô Acid-Albumin & Cetyltrimethylammonium bromide (CTAB)- most frequently used screening tests; turbidity tests and the metachromatic staining spot tests.

Ô Acid-Albumin & CTAB g thick, white turbidity is positive result

Ô Metachromatic Stain- uses basic dyes to react with acid mucopolysaccharides (eg: Azure A dye) Positive result: BLUE spot that cannot be washed away by a dilute acidified methanol solution



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PURINE DISORDERS

Ô Lesch-Nyhan Disease g inherited as a sex-linked recessive results in a massive excretion of urinary uric acid crystals

Ô Failure to inherit the gene to produce the enzyme hypoxanthine guanine phosphoribosyltransferase; responsible for the accumulation of uric acid throughout the body.

Ô Patients suffer from severe motor defects, mental retardation, tendency toward self-destruction, gout & renal calculi

Ô Uric Acid crytals resembling orange sand in diapers

CARBOHYDRATE DISORDERS

Ô Presence of increased urinary sugar (mel ituria) Ô Pentosuria one of Garrod’s original six inborn errors of

metabolism; ingestion of large amounts of fruits Ô Presence of galactosuria indicating the ability to properly

metabolize galactose to glucose. Resulting galactosemia with toxic intermediate metabolic products results in infant failure to thrive, combined with liver disorders, presence of cataracts & severe mental retardation.

Ô Lactosuria may be seen during pregnancy Ô Fructosuria associated with parenteral feeding

Vii. Urine Screening for Metabolic Disorders

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