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Porphyrin tests
Also known as : [PBG],[Plasma fluorescence],[Porphobilinogen],[Porphyrias],[Porphyrins]



Test performed by: LabPLUS Special Chemistry


Specimen Collection

Test request

Tests performed

Specimen

urine porphyrins

1. PBG (porphobilinogen)

2. total urine porphyrins

10 mL casual urine in plain container

protect from light  

blood porphyrins

1. total RBC porphyrins

2. plasma fluorescence

3. zinc protoporphyrin 

4 mL heparinised blood

(dark green top)

protect from light

faecal porphyrins

  total faecal porphyrins

10g faeces (golf ball size)

"Freeze sample and send on ice."

protect from light

As porphyrins are light sensitive, all specimens must be kept in the dark;   usually this is done by wrapping the specimen in foil.

Porphyrin profile (HPLC analysis) of urine or faecal porphyrins will be done automatically if the total porphyrins are increased.

Plese note below for PBG quantitation:

Specimens are sent to CHCH for analysis depending on the screen test. This will be performed by Specialist chemistry staff prior to sendaway.

WHAT SPECIMENS TO SEND:

For suspected acute attack of porphyria (abdominal pain,  with or without autonomic or neurological abnormalities or skin lesions):

For a patient with skin lesions:

The patient should refrain from taking Vitamin B supplements a day before collection because riboflavin (Vitamin B2) interferes with the urine porphyrin test. However, PBG is unaffected and collection in acute presentations should proceed regardless of vitamin intake, so as not to miss a possible diagnosis of acute porphyria


Reference Intervals

Urine PBG :  <10 umol/L 

Urine PBG/creatinine ratio :  < 1.5 umol/mmol

Urine total porphyrins : <320 nmol/L

Urine total porphyrin/creatinine ratio

Adults and children >9y:  <35 nmol/mmol

Children <9y: <75 nmol/mmol

Faecal porphyrins :  <200 umol/Kg dry weight

Red cell porphyrins : <1.8 umol/L RBCs . Increased up to 10 umol/L in iron deficiency.



Assay Method

Urine and faecal total porphyrins, urine PBG: spectrophotometry

Blood and plasma porphyrins:  spectrofluorimetry 

Urine and faecal porphyrin profile : HPLC with fluorescence detection


Diagnostic Use and Interpretation

ACUTE PORPHYRIA:

Acute intermittent porphyria, porphyria variegata and hereditary coproporphyria can present with an acute porphyric attack.  The attack is characterised by abdominal pain which can be severe enough to mimic an acute abdomen.  This may be associated with  neurological and/or autonomic symptoms.  It is very unlikely that neurological symptoms in the absence of abdominal pain are due to an acute porphyric attack.   A raised urine PBG (porphobilinogen) is the diagnostic hallmark of an acute attack of porphyria.

If an acute porphyric attack is suspected, submit a casual urine, preferably at the time of the attack and request   urine porphyrins including PBG , marking the form as URGENT. 

PBG concentrations subside rapidly after the onset of an acute attack;  early collection of the urine sample is important if the diagnosis is to be made.  A normal urine PBG  taken during an episode of acute symptoms excludes an acute attack of porphyria as the cause.

It is also helpful to collect faecal and blood specimens during the acute phase, as the levels of porphyrins are much higher than in remission.

NON-ACUTE POPHYRIAS:

This includes porphyria cutanea tarda (PCT), the acute porphyrias in remission, and the erythropoietic porphyrias. Photosensitivity is a feature, and may range from a diffuse sunburn-like rash (typical of EPP) to blisters with scarring.

PCT is the most common porphyria, and can be diagnosed on a urine sample alone.

Porphyria variegata and hereditary coproporphyria require both urine and faecal samples, and a blood sample is also helpful.

The erythropoietic porphyrias (EPP - erythropoietic protoporphyria, and CEP - congenital erythropoietic porphyria) require a blood sample for diagnosis.

Urine porphobilinogen screening
Urine porphobilinogen screening

Comment 1

The urine sample is diluted especially if applied to male, teenagers and young adults, hence a false negative result cannot be excluded. Suggest recollection while the patient is symptomatic to confirm the result.

 

Comment 2

The raised urine porphobilinogen (PBG) is strongly suggestive of an acute attack of porphyria. The specimen will be forwarded to Canterbury Health laboratories for quantitative PBG testing.

 

Comment 3

A raised urine porphobilinogen (PBG) is suggestive of an acute attack of porphyria. The specimen will be forwarded to Canterbury Health laboratories for quantitative PBG testing.

 

Comment 4

A mildly raised spot urine PBG can suggest an acute attack of porphyria, especially in female. However the urine sample is moderately concentrated, hence a false positive result cannot be excluded. Suggest clinical correlation and if indicated, suggest recollection while the patient is symptomatic to confirm the result.

 

Comment 5

A raised urine porphobilinogen (PBG) is found which is suggestive of an acute attack of porphyria. The specimen will be forwarded to Canterbury Health laboratories for quantitative PBG testing.

 

Comment 6

A raised spot urine PBG can suggest an acute attack of porphyria. However the urine sample is very concentrated, hence a false positive result cannot be excluded. Suggest clinical correlation and if indicated, suggest recollection while the patient is symptomatic to confirm the result.?


Contact Information

Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.

If the query concerns a specific patient please include the NHI number in your email.

If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).

Individual chemical pathologists may be contacted but will not be available at all times. 

After-hours : contact  Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.


Dr Cam Kyle (Clinical Head): CampbellK@adhb.govt.nz   ext 22052 

Dr Weldon Chiu: WeldonC@adhb.govt.nz   ext. 23427 

Dr Leah Ha: LHa@adhb.govt.nz  ext. 23427

Dr Samarina Musaad: SamarinaM@adhb.govt.nz ext. 22402 

Dr Leo Lam: ChiSingL@adhb.govt.nz  ext 22574


Specimen Transport Instructions for Referring Laboratories

Porphyrin: Heparin (whole blood) , Faeces, Urine - Protect from light - Do not spin.

Urine porphyrin -Addition of 5g of NaCO 3 is not required for casual urines. 5g of NaCO 3 should be added to 24 hr collects."

Faecal porphyrins - Sample should be frozen

PBG Quantification

Send to CHCH for testing

  Note: Sendaway procedure will be initiated by Specialist chemistry staff only.



Last updated at 10:45:50 26/07/2021