Porphyrins Quantitative, 24 Hour Urine (Sendout)

High-Performance Liquid Chromatography (HPLC) with Fluorometric Detection

• Includes quantitation of coproporphyrins, uroporphyrins, and intermediate porphyrins (heptacarboxyl, hexacarboxyl, and pentacarboxyl).
• Includes liquid chromatography-tandem mass spectrometry (LC-MS/MS) determination of porphobilinogen.

Cautions: Urine preservative should be used; 24-hour collections should be preserved by adding 5.0 g of sodium carbonate to a light-resistant collection container prior to beginning collection. Porphobilinogen (PBG) and porphyrins are susceptible to degradation at high temperature, at pH below 5.0, and on exposure to light.

Neither erythropoietic protoporphyria nor X-linked dominant protoporphyria are detected utilizing urine porphyrins and PBG measurements.

Ethanol and a variety of medications are known to interfere with heme synthesis leading to elevations in urine porphyrins, particularly coproporphyrin. Coproporphyrin elevation without concomitant PBG elevation should not be used as the basis for the diagnosis of porphyria but may warrant follow-up testing with fecal porphyrin analysis.

24-hour Urine Collection (preferred):

• Before collection, add 5 g of sodium carbonate as preservative to a amber polyethylene 24-hr urine collection container. Do not substitute sodium bicarbonate for sodium carbonate.
  • The addition of preservative must occur prior to beginning the collection.
• Refrigerate and protect sample from light during collection.
• Deliver sample to the lab for processing as soon as possible after completion of collection.

Also acceptable: Unpreserved random urine. Collect Monday-Thursday only. Random samples must arrive at Mayo within 72 hours of collection. Refer to separate entry Porphyrins Quantitative, Random Urine (Sendout) [RUPORR] for collection and processing instructions.

Outside Laboratories:

• Mix specimen well. Measure and record total volume. Document the total volume and collection interval on the DLMP requisition.
• Transfer urine to a light-protected aliquot, leaving room for expansion, and freeze at -20°C as soon as possible after completion of collection. Transport on dry ice.

24-Hour Specimens:

• Measure and record total volume. Document the total volume and collection interval on the requisition.
• Aliquot 50 mL urine (minimum 15 mL) into a light-protected (amber), screw-cap container.
• If necessary, adjust the pH using sodium carbonate to between 7 and 10.
• Promptly freeze the urine aliquot at -20°C.

Result-at-entry:

• RUPRTV (Porphryin Total Volume): <Enter the total volume in mL>
• RUPRIN (Porphryin Interval): <Enter the interval in hr>

Sendouts:

• Order Mayo Test: PQNU.
• Interfaced: Yes.
• If provided, list the patient's medications in the "Performing Lab Comments" section of the MayoAccess order.

Stability:

• 24-Hour Specimens (After completion of collection): Frozen: 7 days.