Allergy Skin Test Interpreter Calculator

Wheal and flare measurement interpretation.

Medical Disclaimer

This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.

Inputs

Wheal diameter (mm)

Flare diameter (mm)

Histamine control wheal (mm)

Saline control wheal (mm)

Tab to move between fields

Results

Reaction grade (0-4+)

Clinically positive (0/1)1

Net wheal (mm)5

Wheal/histamine ratio1.25

Sensitivity level (0-4)2

Test valid (0/1)1

Flare Significant1

How to Use This Calculator

Enter Wheal diameter (mm), Flare diameter (mm), and Histamine control wheal (mm).
Set Saline control wheal (mm).
Review the Reaction grade (0-4+) result.
Use Clinically positive (0/1) and Net wheal (mm) to inform your decision.

What each input means

Wheal diameter (mm): Mean wheal diameter of the allergen test (average of longest + perpendicular).
Flare diameter (mm): Mean erythema/flare diameter surrounding the wheal.
Histamine control wheal (mm): Positive control (histamine) wheal diameter. Must be >=3mm for valid test.
Saline control wheal (mm): Negative control (saline) wheal diameter. Should be <=2mm.

What each result means

Reaction grade (0-4+): Skin test grading: 0 = negative, 4+ = strongly positive.
Clinically positive (0/1): 1 = positive reaction (wheal >=3mm above negative control).
Net wheal (mm): Wheal diameter minus negative control.
Wheal/histamine ratio: Allergen wheal relative to positive control.
Sensitivity level (0-4): 0 = not sensitized, 4 = highly sensitized.
Test valid (0/1): 1 = controls within acceptable range.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Wheal diameter (mm) = 5, Flare diameter (mm) = 15, Histamine control wheal (mm) = 4, Saline control wheal (mm) = 0 = 4 input(s) provided
Calculate Reaction grade
3 = 3
Calculate Clinically positive
Clinically positive
1 = 1
Calculate Net wheal
Net wheal
5 = 5