Untitled Quiz

Study Notes

Urine screening is used for identifying metabolic disorders, including tryptophan disorders.
Tryptophan disorders are a group of inherited conditions affecting tryptophan metabolism.
One disorder, Hartnup Disease, is a rare inherited disorder where increased amounts of tryptophan are converted to indole.Excess indole is reabsorbed from the intestine into the bloodstream, converted to indican in the liver, and excreted in the urine.
Another disorder, Blue Diaper Syndrome, involves abnormal amounts of indican in the urine.
5-Hydroxyindoleacetic acid (5-HIAA) is elevated in argentaffinoma, a type of carcinoid tumor.
Normal daily excretion of 5-HIAA is 2-8 mg; >25 mg/24h suggests argentaffinoma.

Indicanuria (Hartnup Disease) involves increased tryptophan conversion to indole. Excess indole is reabsorbed, converted to indican, and excreted in the urine, which oxidizes to indigo blue. It has a good prognosis if dietary supplements, including niacin, are administered.
5-Hydroxyindoleacetic acid (5-HIAA) is elevated in argentaffinoma, a type of carcinoid tumor.

Cystinuria results in elevated cystine in urine due to impaired renal tubule cystine reabsorption.
Cyanide-nitroprusside test detects cystine: place 3 mL urine in a tube, add 2 mL sodium cyanide, wait 10 minutes, add 5% sodium nitroprusside, observe for red-purple color.

Defects in methionine metabolism cause increased homocysteine.
Elevated homocysteine levels can lead to cataracts, intellectual disability, thromboembolic issues, stroke, and death.
Screening is performed using MS/MS.
Early detection and dietary changes alleviate problems.
Cyanide nitroprusside test followed by silver nitroprusside test.
Silver Nitroprusside Test for Homocysteine: - Place 1 mL urine in a tube. - Add 2 drops of concentrated NH4OH. - Add 0.5 mL of 5% silver nitrate. - Wait 10 minutes.
- Add 5 drops of sodium nitroprusside.
- Observe for red-purple color.

Porphyrins are intermediate compounds in heme production.
Porphyria is a collective term for disorders of porphyrin metabolism, either inherited or acquired through erythrocytic or hepatic malfunctions, or toxic agent exposure.
Common causes of acquired porphyrias include lead poisoning, excessive alcohol intake, iron deficiency, chronic liver disease, and renal disease.
Inherited porphyrias are rarer and caused by enzyme deficiencies in the heme synthesis pathway.
An indication that porphyrinuria may be present is the observation of a red or port wine urine color.
Urine screening is often done using Ehrlich reaction and fluorescence under ultraviolet light.
Ehrlich test is performed after adding acetyl acetone to convert ALA to porphobilinogen.
Porphyrin precursors (ALA, porphobilinogen) in the urine are used for diagnosis.

Lesch-Nyhan disease is an X-linked recessive disorder that leads to massive urinary uric acid excretion, resulting from a defective enzyme (hypoxanthine-guanine phosphoribosyltransferase).
Patients with Lesch-Nyhan disease experience severe motor problems, intellectual disability, self-destructive tendencies, gout, and renal calculi.
Symptoms may manifest normally for the first 6-8 months, often identified by uric acid crystals in diapers similar to orange sand.

Galactosuria is an inability to properly metabolize galactose to glucose.
Galactosemia results from toxic intermediate metabolites causing failure to thrive, liver disorders, cataracts, and severe intellectual disability in infants.
Early detection and excluding lactose from the diet can prevent symptoms.
Galactosemia can be caused by deficiencies in galactose-1-phosphate uridyl transferase, galactokinase, and UDP-galactose-4-epimerase.
Newborn screening detects deficiencies in GALT, measured in red blood cells (heel puncture).