Biochemical Diagnosis of Acute Hepatic Porphyria

Essential Testing Protocol

The American Gastroenterological Association recommends measuring urine aminolevulinic acid (ALA) alongside porphobilinogen (PBG) and creatinine in a random urine sample as the first-line biochemical test for diagnosing acute hepatic porphyria, with both markers typically elevated at least 5-fold above normal during acute attacks 1, 2
Initial biochemical diagnosis requires simultaneous measurement of urinary ALA, PBG, and creatinine, all from a single random urine sample, preferably morning spot urine 2, 3
A 24-hour urine collection is not recommended and should be avoided, as the elevations during acute attacks are sufficiently high that a random sample is adequate 1, 4

Both ALA and PBG are elevated at least 5-fold (often >10-fold) above the upper limit of normal during acute attacks, making the diagnosis straightforward 1, 2, 4
PBG is the most specific marker, and if significantly elevated (>10 times upper limit of normal, or >10 μmol/mmol creatinine), it confirms an acute porphyria attack with high certainty 3
ALA is less specific than PBG and can be elevated in other conditions, including lead poisoning and hereditary tyrosinemia, which is why both must be measured together 3
In patients with recurrent acute attacks, ALA and PBG typically remain elevated even at baseline between attacks 1, 2
If both ALA and PBG are normal during symptoms suggestive of acute attacks, AHP is effectively ruled out as the etiology (with the rare exception of ALAD deficiency porphyria where only ALA is elevated) 1, 4

Never use urine porphyrins alone as a screening test, as this is the most common diagnostic error, and mild and nondiagnostic elevations in urinary porphyrins can be incorrectly interpreted as indicating AHP 1, 2, 4
Do not rely on qualitative tests (Watson-Schwartz or Hoesch tests) alone, and always use quantitative ALA and PBG measurements for definitive diagnosis 2, 4
Hemin treatment can lower or normalize PBG excretion if sampling occurs during or shortly after treatment, potentially causing false-negative results 3, 4

Once biochemical testing confirms elevated ALA and PBG, genetic testing is mandatory to confirm the diagnosis and identify the specific type of acute hepatic porphyria by sequencing ALAD, HMBS, CPOX, and PPOX genes 1, 2, 4
Genetic testing should never be used as first-line screening (except in Scandinavian populations with founder mutations) because most carriers of pathogenic variants never develop symptoms 2, 3
First-degree family members require genetic screening once the pathogenic variant is identified in the proband 2, 4

Consider AHP in any patient, especially women of childbearing age, presenting with unexplained recurrent severe abdominal pain, as diagnosis is frequently delayed by an average of 15 years from symptom onset 1, 2
Both ALA and PBG can be measured with high sensitivity and specificity using modern LC-MS/MS methods, though results often require 1-2 weeks from large reference laboratories 1

A single random (preferably morning) urine sample measuring porphobilinogen (PBG), δ‑aminolevulinic acid (ALA), and creatinine is the American Gastroenterological Association’s recommended first‑line test for suspected acute hepatic porphyria. PBG and ALA are typically elevated ≥5‑fold (often >10‑fold) during an acute attack. 5
Both ALA and PBG must be quantified together because isolated ALA elevation is less specific and can occur in lead poisoning or hereditary tyrosinemia. 5

PBG ≥ 5‑fold and ALA ≥ 5‑fold above normal → strongly indicative of an acute hepatic porphyria; proceed to targeted genetic testing to differentiate AIP, VP, HCP, or ALAD porphyria. 5
Isolated ALA elevation → first rule out lead exposure and hereditary tyrosinemia by checking lead levels and urine organic acids; consider the rare ALAD‑deficiency porphyria. 5
PBG at the upper limit of normal during ongoing symptoms → does not support an acute porphyria attack; alternative diagnoses should be explored.

After biochemical confirmation (≥5‑fold rise in both ALA and PBG), sequencing of the ALAD, HMBS, CPOX, and PPOX genes is mandatory to confirm the diagnosis and identify the specific acute hepatic porphyria subtype. 5

Biochemical testing yields the most reliable results when performed during symptomatic episodes, because PBG and ALA concentrations peak during acute attacks. 5
Samples must be protected from light and refrigerated or frozen promptly to prevent degradation.

Acute hepatic porphyria should be considered in any patient—particularly women aged 15–50 years—who presents with unexplained recurrent severe abdominal pain; the diagnosis is frequently delayed by an average of 15 years from symptom onset. 5
Clinical features alone lack sufficient specificity; definitive biochemical confirmation is essential for accurate diagnosis. 6
Many more common disorders can cause secondary abnormalities in porphyrin accumulation and excretion, underscoring the need for careful interpretation of test results. 6