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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Genetics · Acute Intermittent Porphyria

The Biology and Diagnosis of AIP

At a Glance

Acute Intermittent Porphyria (AIP) is diagnosed through a two-step process: a biochemical urine test taken during an active pain attack to detect elevated PBG levels, followed by genetic testing of the HMBS gene to confirm the specific mutation.

To understand Acute Intermittent Porphyria (AIP), it helps to view your body as a high-precision chemical factory. In this factory, your liver is responsible for building heme, a vital component for blood and detoxification. AIP occurs when a specific part of this production line is understaffed due to a genetic change.

The Biological Bottleneck

Your body builds heme in a series of steps. The HMBS gene provides the instructions for an enzyme called porphobilinogen deaminase (PBGD) [1]. This enzyme is the “worker” at the third step of the production line.

In someone with AIP, this worker is only about 50% efficient [2]. Normally, the liver compensates, and the factory runs smoothly. However, when a trigger (like a certain drug or fasting) hits, the body demands a massive increase in heme production. The first worker on the line (ALAS1) speeds up dramatically [3][4]. But because the third worker (PBGD) is deficient, a “bottleneck” occurs. Two chemical building blocks, ALA (5-aminolevulinic acid) and PBG (porphobilinogen), pile up because they have nowhere to go [4][5]. These precursors are neurotoxic, meaning they irritate and damage your nerves, leading to the symptoms of an attack [6][7].

Why Timing is Everything in Diagnosis

The most important rule of AIP diagnosis is this: Biochemical testing must happen during an attack.

When you are not experiencing an attack, your liver’s “factory” is often balanced, and your levels of ALA and PBG may return to near-normal levels [8]. If you are tested during a period of wellness, the results may be falsely “normal,” leading to years of missed diagnoses [2]. A random urine test (not a 24-hour collection) taken while you are in pain is the gold standard for catching the disease in action [9][10].

The Two-Step Diagnostic Process

Diagnosis is a two-step journey that combines chemistry and genetics:

  1. Biochemical Testing (The “Crisis” Check): Doctors look for a massive rise in urinary PBG (often 10 to 100 times the normal level) [2][11]. This confirms that your current symptoms are caused by a porphyria crisis.
  2. Genetic Testing (The “Source” Check): Once the biochemical levels confirm a crisis, HMBS gene analysis is used to find the specific mutation [12]. This is vital for testing your family members and confirming exactly which type of porphyria you have [13].

Differentiating AIP from “Normal” Pain

AIP is often called “the little imitator” because it looks like appendicitis or gallbladder issues. However, there are key differences that help doctors tell them apart:

  • The “Invisible” Pain: In AIP, a patient may be in agony, but a CT scan or ultrasound will usually show a perfectly normal-looking abdomen with no inflammation [2][14].
  • Extra-Abdominal Clues: Unlike a stomach bug, AIP attacks are often joined by a rapid heart rate (tachycardia), high blood pressure, and low blood sodium levels (hyponatremia) [15][16][17].

Your Diagnostic Checklist

To ensure your medical record is complete and your diagnosis is “bomb-proof” for future doctors, ensure you have the following:

  • [ ] Quantitative Urine PBG: Measured during an active attack and corrected for creatinine.
  • [ ] Quantitative Urine ALA: Measured alongside PBG during the same attack.
  • [ ] HMBS Genetic Variant Analysis: Identifies the specific mutation in your DNA.
  • [ ] Baseline Lab Profile: Including a recent sodium level (to check for hyponatremia).

Common questions in this guide

Why do I need to be tested for AIP during an active attack?
Biochemical testing must happen during an attack because your levels of ALA and PBG often return to near-normal levels when you are not in pain. If you are tested during a period of wellness, the results may be falsely normal and lead to a missed diagnosis.
What is the two-step diagnostic process for AIP?
Diagnosis starts with a biochemical random urine test during an attack to look for massively elevated levels of PBG. If those levels indicate an ongoing crisis, doctors will then order HMBS genetic testing to find your specific mutation and confirm the exact type of porphyria.
How is the pain from an AIP attack different from appendicitis or a stomach bug?
AIP often causes severe, invisible abdominal pain that doesn't show physical inflammation on a CT scan or ultrasound. Unlike typical stomach issues, an AIP attack is frequently accompanied by extra clues like a rapid heart rate, high blood pressure, and low blood sodium levels.
Why does my urine change color during an AIP attack?
During a severe attack, the sudden build-up of chemical precursors called ALA and PBG can cause your urine to change color. Patients often describe it as looking like dark tea or red wine.
What triggers an acute porphyria attack?
Attacks occur when the body suddenly demands more heme production. Common triggers include fasting or certain drugs, which overwhelm the deficient enzyme and cause toxic chemicals to build up and irritate the nerves.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.During my pain episodes, can we perform a 'random' urine test to measure my PBG, ALA, and creatinine levels?
  2. 2.If my urine PBG was elevated, should we proceed with HMBS genetic testing to confirm the specific mutation?
  3. 3.How do my current symptoms and laboratory findings (like sodium levels) differ from more common causes of abdominal pain?
  4. 4.If my genetic test is positive but my urine levels are normal when I am not in pain, what does that mean for my diagnosis?
  5. 5.Can you help me document my diagnosis so I have it ready if I need to go to an emergency room during an attack?

Questions For You

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References

References (17)
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    Acute intermittent porphyria: a test of clinical acumen.

    Dhital R, Basnet S, Poudel DR, Bhusal KR

    Journal of community hospital internal medicine perspectives 2017; (7(2)):100-102 doi:10.1080/20009666.2017.1317535.

    PMID: 28638573
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    Acute Hepatic Porphyrias: Review and Recent Progress.

    Wang B, Rudnick S, Cengia B, Bonkovsky HL

    Hepatology communications 2019; (3(2)):193-206 doi:10.1002/hep4.1297.

    PMID: 30766957
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    Cutting-Edge Therapies and Novel Strategies for Acute Intermittent Porphyria: Step-by-Step towards the Solution.

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    Biomedicines 2022; (10(3)) doi:10.3390/biomedicines10030648.

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    Pilot study of mitochondrial bioenergetics in subjects with acute porphyrias.

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    Molecular genetics and metabolism 2019; (128(3)):228-235 doi:10.1016/j.ymgme.2019.05.010.

    PMID: 31153822
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    Acute Intermittent Porphyria: Novel Etiologic and Pathogenic Therapies Based on RNA Transfer to the Liver.

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    Hepatology (Baltimore, Md.) 2019; (70(3)):1061-1063 doi:10.1002/hep.30678.

    PMID: 31026336
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    Xenobiotics Triggering Acute Intermittent Porphyria and Their Effect on Mouse Brain Respiratory Complexes.

    Zuccoli JR, Martínez MDC, Vallecorsa P, Buzaleh AM

    Journal of xenobiotics 2024; (14(1)):308-319 doi:10.3390/jox14010019.

    PMID: 38535494
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    Liver Transplantation for Acute Intermittent Porphyria: Biochemical and Pathologic Studies of the Explanted Liver.

    Yasuda M, Erwin AL, Liu LU, et al.

    Molecular medicine (Cambridge, Mass.) 2015; (21()):487-95 doi:10.2119/molmed.2015.00099.

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    Recurrent symptoms of acute intermittent porphyria after biochemical normalization with givosiran-An ongoing clinical conundrum.

    Ma CD, Faust D, Bonkovsky HL

    JIMD reports 2023; (64(2)):146-149 doi:10.1002/jmd2.12354.

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    An easily overlooked disease in the early stages: acute intermittent porphyria.

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    Effect of Menstrual Cycle on Acute Intermittent Porphyria.

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    Protocol For Patients With Suspected Acute Porphyria.

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    A case report of acute intermittent porphyria leading to severe disability.

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    Functional and structural analysis of a novel splice site HMBS variant in a Chinese AIP patient.

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    A Diagnostic Challenge in the Emergency Department: Acute Intermittent Porphyria Unmasked After Cabergoline Exposure.

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This page provides educational information about the biology and diagnosis of Acute Intermittent Porphyria (AIP). Always consult your healthcare provider or a medical geneticist for medical testing, diagnosis, and treatment of your specific symptoms.

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