Specimen requirement

Spot urine:

Plain urine bottle

Volume: 10 mL

Authorisation code required

No

24 Hr available service

No

Precaution

Avoid using morning or evening urine or samples obtained after excessive fluid intake by patients.

Urine collected in a light-shield container and delivered to the laboratory without delay.

Method

Spectrophotometry

Reference interval

(Source: from manufacturer’s kit insert)

Clinical indication

Both urinary ALA and PBG are increased in the three neurological porphyriaes, i.e. acute intermittent porphyria, variegate porphyria, and coproporphyria.       

Only ALA not PBG is elevated in lead poisoning and tyrosinemia.

Result interpretation

Increased in urine PBG excretion is a characteristic biochemical feature of acute intermittent porphyria, variegate porphyria and coproporphyria during an acute attack.

In latent phase, PBG concentration in urine may or may not be increased.  Therefore, screening test for PBG should be reserved for symptomatic patients suspected to have neuropathic porphyria.

A negative screening test is usually reliable to rule out the diagnosis in a symptomatic patient.      

(See also urine porphyrin.)

Measurement of uncertainty

See table.

Frequency of measurement

Weekly