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Epic Code LAB120 Pyridoxal 5-Phosphate, Plasma

Important Note

  • Vitamin B6
  • Protect specimen from light
  • Fasting specimen required -overnight (12-14 hours) (infants-draw prior to next feeding).
  • Patient must not ingest vitamin supplements for 24 hours before the specimen is drawn.

Additional Codes

Name Alias: Vitamin B6

Mayo Code: PLP

Interface Order Alias: 10651

Cerner: 8240

Epic: LAB 120

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful For

Determining vitamin B6 status, including in persons who present with progressive nerve compression disorders, such as carpal tunnel and tarsal tunnel syndromes


Determining the overall success of a vitamin B6 supplementation program


Diagnosis and evaluation of hypophosphatasia

Specimen Type

Plasma Heparin

Shipping Instructions

Ship specimen in amber vial to protect from light.

Specimen Required

Patient Preparation:

1. Fasting-overnight (12-14 hours) (infants-collect specimen prior to next feeding). Water can be taken as needed

2. For 24 hours prior to specimen collection, patient must not take multivitamins or vitamin supplements.


Supplies: Amber Frosted Tube, 5 mL (T192)

Collection Container/Tube: Green top (sodium or lithium heparin) or plasma gel separator (PST)

Submission Container/Tube: Amber vial

Specimen Volume: 1 mL

Collection Instructions:

1. Centrifuge at 4° C within 2 hours of collection

2. Aliquot all plasma into amber vial and freeze immediately.

Laboratory Test Directory Note:

COLLECTION NOTE: Volumes listed are in serum or plasma, draw approximately 2 1/2 times the requested volume in whole blood.

Specimen Minimum Volume

0.75 mL


If not ordering electronically, complete, print, and send a General Request (T239) with the specimen.

Specimen Stability Information

Specimen Type Temperature Time Special Container
Plasma Heparin Frozen 29 days LIGHT PROTECTED

Reject Due To

Gross hemolysis OK
Gross lipemia OK
Gross icterus OK


Reference ranges were established using healthy fasting volunteers who abstained from vitamin supplementation for 24 hours prior to collection. Vitamin supplementation and nonfasting may result in elevated plasma vitamin concentrations.

Clinical Information

Vitamin B6 is a complex of 6 vitamers: pyridoxal, pyridoxol, pyridoxamine, and their 5'-phosphate esters. Due to its role as a cofactor in many enzymatic reactions, pyridoxal phosphate (PLP) has been determined to be the biologically active form of vitamin B6.


Vitamin B6 deficiency is a potential cause of burning mouth syndrome and a possible potentiating factor for carpal tunnel and tarsal tunnel syndromes. Persons who present chronic, progressive nerve compression disorders may be deficient in vitamin B6 and should be evaluated. Vitamin B6 deficiency is associated with symptoms of scaling of the skin, severe gingivitis, irritability, weakness, depression, dizziness, peripheral neuropathy, and seizures. In the pediatric population, deficiencies have been characterized by diarrhea, anemia, and seizures.


Markedly elevated PLP in conjunction with low levels of pyridoxic acid are observed in cases of hypophosphatasia, a disorder characterized by low levels of alkaline phosphatase and a range of skeletal abnormalities.

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Report Available

1 to 4 days

Reporting Name

Pyridoxal 5-Phosphate (PLP), P

Reference Values

5-50 mcg/L


Levels for fasting individuals falling in the range of 3 to 30 mcg/L for pyridoxic acid (PA) and 5 to 50 mcg/L for pyridoxal 5-phosphate (PLP) are indicative of adequate nutrition.


The following are interpretative guidelines based upon PLP and PA results:

If PLP is >100 mcg/L and PA is ≤30:

-The increased pyridoxal 5-phosphate is suggestive of hypophosphatasia. Consider analysis of serum alkaline phosphatase isoenzymes (ALKI / Alkaline Phosphatase, Total and Isoenzymes, Serum) and urinary phosphoethanolamine (AAPD / Amino Acids, Quantitative, Random, Urine).


If PLP is >100 mcg/L and PA is 31 to 100 mcg/L or PLP is 81 to 100 mcg/L and PA is < or=30 mcg/L:

-The increased pyridoxal 5-phosphate is likely related to dietary supplementation; however, a mild expression of hypophosphatasia cannot be excluded. Consider analysis of serum alkaline phosphatase isoenzymes (ALKI / Alkaline Phosphatase, Total and Isoenzymes, Serum) and urinary phosphoethanolamine (AAPD / Amino Acids, Quantitative, Random, Urine).


If PLP is 51 to 80 mcg/L or PLP is 81 to 100 mcg/L and PA is >30; or PLP is >100 mcg/L and PA is >100 mcg/L:

-The elevated pyridoxal 5-phosphate is likely due to dietary supplementation.

Method Description

The stable isotope pyridoxal 5-phosphate-d2 and/or pyridoxic acid-d2 is added to plasma as an internal standard. Meta-phosphoric acid solution is then added to precipitate the proteins. Following sedimentation of the proteins, an aliquot of the clarified supernatant fluid is subjected to separation of pyridoxal 5-phosphate, pyridoxic acid, and internal standards from other plasma components by reverse-phase high-performance liquid chromatography with quantitation by tandem mass spectrometry.(Unpublished Mayo method)

Day(s) Performed

Monday through Thursday, Saturday, Sunday

Clinical Reference

1. Kimura M, Kanehira K, Yokoi K: Highly sensitive and simple liquid chromatographic determination in plasma of B6 vitamins, especially pyridoxal 5'-phosphate. J Chromatogr A. 1996;722(1-2):296-301. doi: 10.1016/0021-9673(95)00354-1

2. Ball GFM: Vitamins: Their Role in the Human Body. Blackwell Publishing; 2004;310-325

3. Mackey AD, Davis SR, Gregory JF III: Vitamin B6. In: Shils ME, Shike M, Ross AC, et al. eds. Modern Nutrition in Health and Disease. 10th ed. Lippincott Williams and Wilkins; 2006:452-461

4. Roberts NB. Taylor A. Sodi R: Vitamins and trace elements. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018:639-718

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
PLP Pyridoxal 5-Phosphate (PLP), P 30552-4


Result ID Test Result Name Result LOINC Value
4047 Pyridoxal 5-Phosphate (PLP), P 30552-4
Laboratory Test Directory Additional Information:

Name alias: Vitamin B 6 | B6