Test Catalog

Test ID: DHRF    
Dihydrorhodamine Flow Cytometric N-Formyl-Methionyl-Leucyl-Phenylalanine Test, Blood

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of Rac2 deficiency

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

This assay can be used for the diagnostic evaluation of Rac2 deficiency, which is a neutrophil defect that causes profound neutrophil dysfunction with decreased chemotaxis, polarization, superoxide anion production, azurophilic granule secretion. This disease is caused by inhibitory mutations in the RAC2 gene, which encodes a Rho family GTPase essential to neutrophil activation and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase function.(1) Patients with Rac2 deficiency have been shown to have normal neutrophil oxidative burst when stimulated with phorbol myristate acetate (PMA), indicating normal NADPH oxidase activity, but abnormal neutrophil responses to N-formyl-methionyl-leucyl-phenylalanine (fMLP), which is a physiological activator of neutrophils. The defective oxidative burst to fMLP, but not to PMA, indicates a signaling defect in Rac2 deficiency.(2)

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Result Name


Cutoff for defining normal

% fMLP ox-DHR+


> or =10%



> or =2

Control % fMLP ox-DHR+


> or =10%

Control MFI fMLP ox-DHR+


> or =2


The appropriate age-related reference values for Absolute Neutrophil Count will be provided on the report.

Interpretation Provides information to assist in interpretation of the test results

An interpretive report will be provided, in addition to the quantitative values described in Clinical Information.


Interpretation of the results of the quantitative dihydrorhodamine (DHR) flow cytometric assay has to include both the proportion of positive neutrophils for DHR after N-formyl-methionyl-leucyl-phenylalanine stimulation, and the mean fluorescence intensity.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Specimens are optimally tested within 24 hours of blood draw, though the stability of the assay is within 48 hours of collection. Specimens should be collected in sodium heparin and transported under strict ambient conditions. Use of the Ambient Mailer-Critical Specimens Only box (T668) is encouraged to ensure appropriate transportation of the specimen.


Hemolyzed specimens may give high background. Specimens with an ANC (absolute neutrophil count) below 200 will not be accepted for this assay. Complete myeloperoxidase (MPO) deficiency can yield a false-positive result.

Supportive Data

Dihydrorhodamine (DHR) analysis was performed to assess neutrophil oxidative burst in 157 healthy donors, 74 children, and 83 adults.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Ambruso DR, Knall C, Abell AN, et al: Human neutrophil immunodeficiency syndrome is associated with an inhibitory Rac2 mutation. Proc Natl Acad Sci U S A 2000;97:4654-4659

2. Accetta D, Syverson G, Bonacci B, et al: Human phagocyte defect caused by a RAC2 mutation detected by means of neonatal screening for T cell lymphopenia. J Allergy Clin Immunol 2011;127:535-538