DHA (Docosahexaenoic Acid)
The amount of DHA, an omega-3 fat found in fish and algae, in your blood. It mostly reflects what you ate or took recently.
AI-drafted. Awaiting verificationAlso called DHA, C22:6n-3, 22:6n-3LOINC 35174-2
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What it is
DHA (docosahexaenoic acid) is an omega-3 fat. Your body makes only small amounts, so most of it comes from fatty fish, fish oil and algae-based supplements. DHA is a building block of cell membranes, especially in the brain and eyes. This test measures the DHA in your blood serum or plasma. That includes DHA carried in the fats and phospholipids moving through your bloodstream, so the number can swing with your most recent meals and supplements.
Why it matters
Blood DHA gives a rough picture of how much omega-3 you have been getting from food and supplements. Eating fish is linked to better heart health in many studies, but there is no widely accepted target for DHA in serum or plasma, and results differ a lot between labs and methods. For longer-term omega-3 status, many clinicians use a red blood cell test such as the omega-3 index, which changes more slowly and has better-studied categories.
If it’s low
A low DHA level usually reflects little omega-3 in your recent diet. This is common, especially in people who rarely eat fish. On its own it does not show that anything is wrong, but your clinician can put it in context with your diet and other results.
Common causes
- Eating little or no fish
- A plant-based diet without algae-based omega-3
- Smoking or higher body weight, which are linked to lower omega-3 levels in blood cell studies
- Conditions that make it hard to absorb fat, such as celiac disease or pancreatic problems
What can help
- Eat fatty fish such as salmon, sardines or trout. The American Heart Association suggests two servings of fatty fish a week for people without heart disease
- Ask your clinician whether an omega-3 supplement makes sense for you
If it’s high
A high DHA level usually means you recently ate fatty fish or took fish oil or algae oil. It is not a known sign of illness on its own. Lab method and units also affect the number, so compare it with the range printed on your own report.
Common causes
- Fish oil, cod liver oil or algae-oil supplements
- A recent meal rich in fatty fish, such as salmon, sardines or mackerel, if you were not fasting
- Omega-3 fortified foods and drinks
- Differences in lab method or units
What can help
- Bring a list of the supplements and fish-oil products you take to your next visit
- Ask whether a repeat test after an overnight fast would be useful
What can affect your result
- Recent meals and supplements: fish, fish oil and algae oil can raise serum levels
- Fasting: many labs ask for an overnight fast and no alcohol for 24 hours
- Your usual diet over the past few weeks
- Pregnancy, which shifts fatty acid levels across the trimesters
- Smoking and higher body weight, which are linked to lower omega-3 levels in blood cell studies
- How the lab reports it: an absolute amount (µmol/L) and a percent of total fatty acids are different measurements
- A recent meal, a fish-oil or algae-oil supplement, or alcohol can change serum fatty acid results. Quest's essential fatty acid panel asks for an overnight fast and no alcohol for 24 hours before the draw.
- Labs report this marker in different ways: the absolute amount in the blood (µmol/L, nmol/mL or mg/L), a percent of total fatty acids, or the amount in one fat class such as phospholipids. These are different measurements and should not be compared with each other.
Morning, after an overnight fast, when your lab asks for one. Serum and plasma levels follow recent intake, so they can change fairly quickly after a change in diet or supplements. Red blood cell levels move more slowly and reflect about the past 4 months.
When to talk to a clinician
There is no urgent level for DHA. If your result is far outside the range your lab printed, mention it to your clinician and tell them about any omega-3 supplements you take.
Questions you could ask
- Which omega-3 test is best for following my results over time?
- Is the amount of omega-3 I take still right for me?
- Would a repeat test after an overnight fast be useful?
- Is my diet giving me enough omega-3, and would a supplement make sense for me?
- Would a red blood cell omega-3 test be a better way to track this?
Questions people ask
Why does my result not have a normal range?
There is no widely accepted normal range for DHA in serum or plasma, and what a lab prints depends on its method and units. If your report prints a range, use that one. Your clinician can help put your result in context.
How is this different from the omega-3 index or red blood cell DHA?
Serum or plasma DHA mostly reflects recent intake. Red blood cell tests reflect roughly the past four months, so they change slowly and are used for the omega-3 index, which has published categories. The numbers from the two tests cannot be compared.
Do I need to fast for a DHA test?
Many labs ask for an overnight fast and no alcohol for 24 hours, because a recent meal or supplement can change the result. Follow the instructions from the lab doing your test.
Show the science and sources
Units
- 1 µmol/L = 1 µmol/L
- 1 µmol/L = 1 nmol/mL
- 1 µmol/L = 0.3285 mg/L
For clinicians and researchers
Serum or plasma DHA (22:6n-3) is reported as an absolute concentration of total fatty acid after hydrolysis and methylation of all lipid classes (typically gas chromatography with mass spectrometry or flame ionization; µmol/L or nmol/mL), as a percent of total fatty acids (a separate LOINC, 88995-6), or within one lipid class such as phospholipids. These are not interchangeable. LOINC 35174-2 is the moles/volume code, and no mass/volume DHA code was found. Circulating DHA mainly reflects recent intake, so fasting state matters. Red blood cell DHA and the omega-3 index (EPA + DHA as a percent of RBC fatty acids) are preferred for longer-term status, and equations have been published to convert plasma, serum and whole-blood values to RBC equivalents. No consensus reference interval or outcome-based target exists for absolute serum DHA. Published intervals are cohort- and method-specific, for example trimester-specific serum intervals measured by GC-MS in a Spanish pregnancy cohort. Molecular weight is 328.5 g/mol, so 1 mg/L is about 3.04 µmol/L.
LOINC 35174-2 (primary). Specimen: serum-or-plasma.
Sources
- Docosahexaenoic acid (PubChem CID 445580), NIH National Library of Medicine (PubChem)
- Fatty Acid Panel, Essential (C12-C22), Serum (test details as listed by Fullscript), Quest Diagnostics
- Over Half of the United States Population Had an Undesirably Low Omega-3 Index Based on Erythrocyte Membrane Measurements: Results From the Cross-Sectional NHANES From August 2021 to August 2023, Current Developments in Nutrition (2026)
- Trimester-Specific Reference Ranges for Saturated, Monounsaturated and Polyunsaturated Fatty Acids in Serum of Pregnant Women: A Cohort Study from the ECLIPSES Group, Nutrients (2021)
- NHANES August 2021-August 2023 Data Documentation: Fatty Acids - Washed RBCs (FAR_L), CDC National Center for Health Statistics (2025)
AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.