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Yeast and Pseudohyphae, Nail — Qualitative, KOH Preparation

Published: August 9, 2026Updated: August 17, 2026

Examines nail material for yeast and pseudohyphae, which may support a diagnosis of a fungal nail infection.

Quick summary

["A positive result can indicate yeast-related fungal infection of the nail."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
55310-7
Short code
Yeast pseudohyphae Nail Ql KOH Prep
Synonyms
Yeast pseudohyphae Nail Ql KOH Prep
Category
liver
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
koh-preparation
CPT
84484
SNOMED
302774002
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What is this test?

This test examines a sample of nail material for yeast and pseudohyphae using a potassium hydroxide (KOH) preparation. It is commonly used to help evaluate suspected fungal infection of the fingernail or toenail.

Why might I need this test?

Your clinician may order this test if you have thickened, discolored, brittle, or crumbly nails, or if you have symptoms of a fungal skin infection involving the nail. The test can also be used to check for fungal organisms in skin or nail samples.

How is the test performed?

A clinician collects a small sample from the affected nail or surrounding skin. The specimen is prepared with KOH and examined under a microscope to look for yeast, pseudohyphae, and other evidence of fungal infection.

How do I prepare for the test?

No special preparation is usually required, but follow your clinician's collection instructions. Tell the clinician about any topical antifungal products, nail polishes, or treatments you have recently used, because they may affect the sample.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Nail Yeast and Pseudohyphae (KOH Prep)

Frequently asked questions

What does a positive result mean?
A positive result means yeast or pseudohyphae were seen in the nail sample, which can be consistent with a fungal nail infection. The result alone does not identify the exact organism or determine the severity of the infection.
Does this test detect all types of nail fungus?
No. A KOH preparation primarily helps detect yeast and may detect other fungal forms, but some infections can require culture, molecular testing, or examination of another sample.
Is this the same as a routine fungal culture?
No. This is a rapid microscopic examination of a nail sample, while a fungal culture allows organisms to grow and be identified more specifically. Your clinician may recommend culture if the result is negative but suspicion remains high.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy