Erythrocyte Hydroxymethylbilane Synthase

HMBS, PBG-Deaminase

Clinical Use

  1. This assay is mainly used for family studies in AIP.
  2. Use of PBG deaminase activity to exclude AIP when other investigations are normal may provide misleading information or lead to interpretation difficulties.
  3. This assay is not useful in children less than 1 year old and is affected by erythrocyte disorders and blood transfusion.

Total PBG deaminase activity is reduced by 50% in erythrocytes from patients with clinically manifest AIP and in erythrocytes from those of their relatives, including pre-pubertal children, who have the latent gene defect for the disease. However there is a significant overlap between the normal and affected reference ranges.

Patient preparation

Sample Preparation
10mL of fresh EDTA anti-coagulated blood. Blood porphyrin levels decrease rapidly on exposure to light (the half life is 24hrs).
The minimum volume required for assay is 1.0mL.

Paediatric investigations should be discussed with the laboratory.

Dispatch samples by first class post in a container that conforms to Post Office regulations, protected from light, to arrive in the laboratory with 24-48 hours of sampling. When a delay in dispatch is anticipated, due to weekend or bank holiday, samples should be stored at 0-40C and protected from light.


Routine requests are assayed within 5 working days after receipt of sample. Urgent requests should be discussed with the laboratory and dispatched via a courier service. Results can be telephoned or faxed as soon as they become available.

Reference Ranges:
Normal: 30-67 nmol/h/ml (Cardiff)
20-42 nmol/h/ml (King’s)
AIP 14-33 nmol/h/ml (Cardiff)

Centres offering this assay
Cardiff UHW Porphyria Diagnostic Service
King’s College Hospital Porphyria Service

Frontline tests for the investigation of suspected porphyria. A. C. Deacon & G. H. Elder. J. Clin. Pathol. 2001; 54:500-507

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