Hemoglobin and Hematocrit (Hgb/Hct) Biomarker Testing
It measures your blood’s oxygen-carrying capacity and red cell concentration, with results you can order and review through Vitals Vault at Quest.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
Hemoglobin and hematocrit are two closely related numbers that describe your red blood cells and how well your blood can carry oxygen. They are often checked together because they move in predictable ways when you are anemic, dehydrated, bleeding, or making too many red blood cells.
If you have fatigue, shortness of breath with activity, frequent headaches, dizziness, pale skin, or heavy menstrual bleeding, these results can help explain whether low red blood cells are part of the picture. On the other hand, if you have symptoms like flushing, itching after a hot shower, or you live at high altitude, higher values can point to different next steps.
These tests are not a diagnosis by themselves. They are best used as part of clinician-guided care, alongside your symptoms, medical history, and related labs such as iron studies and a complete blood count (CBC).
Do I need a Hemoglobin and Hematocrit test?
You may want hemoglobin and hematocrit (often written as Hgb/Hct) if you are trying to understand symptoms that could be related to low oxygen delivery, like persistent fatigue, reduced exercise tolerance, lightheadedness, or shortness of breath. They are also commonly checked when you have heavy periods, follow a restrictive diet, have known iron deficiency, or have had recent surgery or blood loss.
Testing can also be useful when you are monitoring a known condition. If you have anemia, kidney disease, inflammatory conditions, or you are pregnant, Hgb/Hct can help track whether your red blood cell levels are stable over time. If you are on treatments that affect red blood cells, such as iron therapy or medications that stimulate red blood cell production, trending results can show whether you are responding.
You might also need this test if your clinician is evaluating high values. Dehydration can temporarily concentrate your blood, but persistently high hemoglobin or hematocrit can be associated with smoking, sleep-disordered breathing, chronic lung disease, living at altitude, or less commonly a bone marrow disorder.
If you are deciding whether to test, it helps to pair Hgb/Hct with context: your symptoms, your hydration status, and companion labs that explain the “why” behind an abnormal result. A single number rarely tells the whole story.
This is a standard blood test run in CLIA-certified laboratories; results support medical decision-making but do not diagnose a condition on their own.
Lab testing
Order hemoglobin and hematocrit testing and schedule your draw at Quest.
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
Vitals Vault lets you order hemoglobin and hematocrit testing without a referral and complete your blood draw at a participating Quest location. If you are comparing options, this can be a straightforward way to get objective data when symptoms are vague or when you want to confirm that a prior abnormal result has improved.
After your results post, you can use PocketMD to put the numbers into plain language and to map reasonable follow-up questions for your clinician. That is especially helpful with Hgb/Hct because the next step depends on the pattern: low values often lead to iron, B12, folate, or bleeding evaluation, while high values often lead to hydration review, oxygen status, and sometimes repeat testing.
If you are tracking a trend, reordering through Vitals Vault makes it easier to compare results over time and decide whether you need a broader panel (such as a CBC or metabolic panel) to understand contributing factors.
- Order online and draw at Quest locations
- PocketMD helps you interpret results and plan next steps
- Easy re-testing to confirm changes and track trends
Key benefits of Hemoglobin and Hematocrit testing
- Helps screen for anemia when fatigue, dizziness, or shortness of breath are unexplained.
- Adds context to heavy menstrual bleeding, recent blood loss, or recovery after surgery.
- Supports monitoring of known anemia and response to iron or other therapies over time.
- Flags possible dehydration-related concentration of blood when hematocrit is temporarily high.
- Can prompt evaluation for low oxygen states (such as sleep-disordered breathing) when values are persistently elevated.
- Pairs well with a CBC and iron studies to clarify whether the issue is production, loss, or dilution of red blood cells.
- Gives you a simple, repeatable metric to discuss with your clinician using PocketMD guidance.
What is Hemoglobin and Hematocrit?
Hemoglobin is the iron-containing protein inside red blood cells that binds oxygen in your lungs and delivers it to your tissues. Hematocrit is the percentage of your blood volume that is made up of red blood cells. Because both reflect red blood cell mass, they usually rise and fall together, but they are measured differently.
Your body tightly regulates red blood cell production. The kidneys release a hormone called erythropoietin (EPO) when oxygen delivery is low, which signals the bone marrow to make more red blood cells. Nutrients like iron, vitamin B12, and folate are also required for healthy red blood cell production, and inflammation or chronic disease can interfere with this process.
Hgb/Hct are often reported as part of a complete blood count, along with red blood cell indices (like MCV) that hint at the cause of anemia. When Hgb/Hct are ordered alone, they still provide a useful snapshot, but abnormal results usually lead to additional testing to find the underlying driver.
How hemoglobin differs from hematocrit
Hemoglobin is a concentration of the oxygen-carrying protein in your blood, while hematocrit is a proportion of blood volume. Hematocrit can shift with changes in plasma volume, so dehydration can raise it even if your total red blood cell mass has not changed much.
Why reference ranges vary
Normal ranges depend on the lab method and on factors like sex assigned at birth, age, pregnancy status, altitude, and smoking. Your report’s reference interval is the right starting point, and trends over time often matter more than a single value.
What do my Hemoglobin and Hematocrit results mean?
Low hemoglobin and/or hematocrit
Low values commonly suggest anemia, meaning you have fewer red blood cells or less hemoglobin than expected. The most common causes include iron deficiency (often from blood loss), anemia of chronic inflammation, vitamin B12 or folate deficiency, and less commonly bone marrow or hemolytic (red cell breakdown) conditions. If your result is low, the next step is usually to confirm the pattern with a CBC and to look for the cause with tests such as ferritin, iron/TIBC, B12, folate, and sometimes a reticulocyte count. If you have chest pain, fainting, severe shortness of breath, or black/tarry stools, you should seek urgent care rather than waiting to retest.
In-range (optimal) hemoglobin and hematocrit
In-range results generally mean your red blood cell level and oxygen-carrying capacity are appropriate for your body and situation. If you still feel fatigued, it does not rule out other contributors such as thyroid issues, sleep problems, iron deficiency without anemia, low B12, infection, or mood-related fatigue. Your clinician may look at other CBC components (MCV, RDW) or iron markers to see whether you are trending toward a deficiency even before hemoglobin drops. If you are monitoring a prior abnormal result, a stable in-range trend is often reassuring.
High hemoglobin and/or hematocrit
High values can happen when your blood is more concentrated (for example, from dehydration or diuretic use) or when your body is making more red blood cells in response to low oxygen. Common contributors include smoking, living at high altitude, chronic lung disease, and sleep-disordered breathing. Persistently high results may require repeat testing when you are well-hydrated and, if still elevated, evaluation for secondary causes and less commonly a bone marrow condition such as polycythemia vera. Because high hematocrit can increase blood viscosity, your clinician may also consider clot risk in the context of your overall health.
Factors that influence hemoglobin and hematocrit
Hydration status is a major confounder: dehydration can raise hematocrit, while overhydration or pregnancy can lower it by dilution. Recent bleeding, heavy menstrual cycles, and frequent blood donation can lower levels, sometimes before symptoms become obvious. Medications and conditions that affect kidney signaling (EPO), inflammation, or nutrient absorption can also shift results. Timing matters too: values can change after acute illness, high-intensity endurance training, or a recent transfusion, so your clinician may recommend repeating the test when you are back to baseline.
What’s included
- Hemoglobin
- Hematocrit
Frequently Asked Questions
What is the difference between hemoglobin and hematocrit?
Hemoglobin measures the concentration of the oxygen-carrying protein inside red blood cells, while hematocrit measures the percentage of your blood volume made up of red blood cells. They usually move together, but hematocrit can be more affected by hydration because plasma volume changes the percentage.
Do I need to fast for a hemoglobin and hematocrit test?
Fasting is not usually required for Hgb/Hct. If your order is bundled with other labs (like lipids or glucose), fasting instructions may apply to the panel, so follow the directions on your lab order.
What causes low hemoglobin and hematocrit?
Common causes include iron deficiency (often from blood loss), anemia of chronic disease/inflammation, vitamin B12 or folate deficiency, and kidney disease. Less common causes include hemolysis or bone marrow disorders. A CBC plus iron studies (ferritin, iron, TIBC) often helps pinpoint the reason.
What causes high hematocrit or high hemoglobin?
Dehydration is a frequent short-term cause. Persistently high values can be related to smoking, high altitude, chronic lung disease, or sleep-disordered breathing, where your body makes more red blood cells to compensate for lower oxygen. Your clinician may repeat the test and consider additional evaluation if it stays elevated.
How often should I retest hemoglobin and hematocrit?
It depends on why you tested. If you are treating iron deficiency anemia, clinicians often recheck in a few weeks to a couple of months to confirm improvement, while chronic conditions may be monitored on a longer schedule. If a result is unexpectedly high or low, repeating when you are well-hydrated and clinically stable can help confirm whether it is persistent.
Is hemoglobin and hematocrit the same as a CBC?
No. A CBC includes hemoglobin and hematocrit plus additional measures like red and white blood cell counts, platelet count, and red blood cell indices (MCV, MCH, RDW). If Hgb/Hct are abnormal, a full CBC often provides important clues about the cause.