Urine Porphobilinogen

Kidney

Report in 192Hrs

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No Fasting Required

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Detects porphobilinogen.

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Urine Porphobilinogen Test Information Guide

Why is it done?
- Detects porphobilinogen, a precursor to heme synthesis that accumulates in acute porphyrias when heme production is disrupted
- Diagnosing acute intermittent porphyria (AIP) and other acute hepatic porphyrias during acute attacks
- Evaluating patients presenting with unexplained acute neurological symptoms, abdominal pain, psychiatric manifestations, or autonomic dysfunction
- Screening at-risk family members of patients with confirmed acute porphyria
- Monitoring disease activity and response to treatment in patients with known porphyria
- Typically performed during acute episodes when symptoms are present; can also be done during remission to establish baseline levels
Normal Range
- Normal Reference Range: Less than 2 mg/24 hours (or <9.4 µmol/24 hours in SI units)
- Some laboratories use <1.5 mg/24 hours or <1.8 mg/24 hours depending on methodology
- Units: mg/24 hours (milligrams per 24-hour collection) or µmol/24 hours (micromoles per 24-hour collection)
- Negative Result: Absence of porphobilinogen (normal finding); suggests porphyria is unlikely
- Positive Result: Elevated PBG levels (typically >2 mg/24 hours); indicates presence of acute porphyria or acute attack
- Markedly Elevated: Levels significantly above 10 mg/24 hours strongly suggest active acute porphyria attack
Interpretation
- Elevated PBG During Acute Attack: Strongly suggests acute intermittent porphyria (AIP), variegate porphyria (VP), or hereditary coproporphyria (HCP); clinical correlation with symptoms is essential
- Persistent Elevation: May indicate ongoing acute phase or severe disease; requires further investigation with plasma porphobilinogen and plasma aminolevulinic acid (ALA) tests
- Normal Results During Symptoms: Does not exclude porphyria in early phases; repeat testing may be necessary during acute exacerbation
- Normal Results During Remission: Expected finding; confirms disease is in remission phase
- False Positives May Occur: With pregnancy, birth control use, hormonal therapy, stress, fasting, certain infections, or menstrual cycle fluctuations
- Factors Affecting Results: Improper urine collection, light exposure, contamination, delays in processing, certain medications (barbiturates, sulfonamides, estrogens), and metabolic stressors can influence levels
- Best Timing for Testing: During acute attack (within 24-72 hours of symptom onset) when PBG levels peak for optimal diagnostic accuracy
Associated Organs
- Primary Organ Systems: Nervous system, hepatic (liver), gastrointestinal system, and endocrine system; metabolic dysfunction affects multiple organ systems
- Acute Intermittent Porphyria (AIP): Most common acute porphyria; presents with acute neurovisceral attacks including severe abdominal pain, psychiatric symptoms, neurological complications, autonomic instability
- Variegate Porphyria (VP): Causes acute attacks similar to AIP plus photosensitivity with blistering skin lesions; increased cardiovascular complications
- Hereditary Coproporphyria (HCP): Presents with acute neurovisceral attacks and photosensitivity; less common than AIP
- Complications of Elevated PBG: Neurovisceral crisis, acute paralysis, respiratory failure requiring mechanical ventilation, cardiac arrhythmias, seizures, severe autonomic dysfunction
- Chronic Manifestations: Hypertension, renal dysfunction, hepatic cirrhosis, neurological sequelae from recurrent attacks, increased risk of hepatocellular carcinoma
- Associated Metabolic Disorders: Porphyrias result from enzyme deficiencies in heme synthesis pathway, primarily affecting liver (delta-aminolevulinic acid synthase regulation)
Follow-up Tests
- Plasma Porphobilinogen (PBG) and Plasma Aminolevulinic Acid (ALA): Essential confirmatory tests; acute porphyria typically shows elevation of both plasma and urine PBG and ALA
- Urine Delta-Aminolevulinic Acid (ALA): Complements PBG testing; typically elevated concurrently in acute attacks; helps differentiate porphyria type
- Porphyrin Studies: Quantitative fecal coproporphyrin, urine coproporphyrin, and urine uroporphyrin; help identify specific porphyria type (VP shows elevated fecal coproporphyrin)
- Genetic Testing: DNA sequencing for PBGD, PPOX, or CPOX gene mutations; confirms diagnosis and identifies carriers in family members
- Acute Phase Labs: Electrolytes, glucose, liver function tests, renal function, magnesium to assess organ involvement during acute attack
- Neurological Assessment: MRI, EMG, or nerve conduction studies if neurological complications suspected; EEG if seizures occur
- Baseline and Monitoring Testing: Repeat PBG testing during remission (every 6-12 months) to establish baseline and monitor disease progression
- Family Screening: First-degree relatives should undergo plasma PBG, plasma ALA, and genetic testing to identify asymptomatic carriers
Fasting Required?
- Fasting: No, fasting is NOT required for urine porphobilinogen collection
- 24-Hour Urine Collection: Standard collection method; patient should discard first morning void, then collect all urine for 24 hours including next morning void
- Container Requirements: Use sterile container provided by laboratory; many contain preservatives (boric acid or acetic acid) to prevent bacterial overgrowth and preserve porphobilinogen
- Light Protection: Keep urine collection away from direct sunlight and protect container from light exposure; store in refrigerator or cool location
- Medications to Consider: Inform physician of all current medications; barbiturates, estrogens, sulfonamides, and other drugs may precipitate attacks and increase PBG levels
- Stress Management: Avoid unnecessary stress, fasting, or extreme exercise before collection; these factors can trigger porphyria attacks and alter results
- Hydration: Maintain normal fluid intake; excessive hydration or dehydration can affect urine concentration and test results
- Specimen Processing: Transport specimen to laboratory promptly; most labs require processing within 2-4 hours of collection completion for optimal results

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