Should I Worry About My Blood Test Results? What to Check First

Your blood test results have arrived: in a patient portal, a lab app, an email or a message from the lab. A few lines are flagged H or L, maybe in red. Your appointment is days or weeks away, or there is no doctor at all because you ordered the tests yourself.

Take a breath. A flag is a signal to look closer, not a diagnosis, and most flags are not emergencies.

You are not alone in feeling uneasy. In a survey of US patients who could see their results before hearing from a doctor, about one in six of those with abnormal results said it made them more worried. Yet nearly all of the people surveyed still wanted their results as soon as they were ready. This guide helps you use that head start well.

In short:

1. Check for anything urgent.
2. Treat a flag as a question, not a diagnosis.
3. Read the report as a whole.
4. Compare with your earlier results.
5. Prepare questions for your doctor.

First: is anything urgent?

Get help right away if you feel unwell

Whatever your results say, seek urgent care or call your local emergency number if you have:

• chest pain or pressure;
• shortness of breath;
• fainting or new confusion;
• black stools, or bleeding that is unusual for you;
• a high fever.

Sort everything else into three groups

A 2025 paper in the Journal of the American Board of Family Medicine suggests labs label each result, from “No immediate concern” to “Contact your doctor.” You can sort your flags the same way:

• Contact your doctor today. A value marked critical, “panic” or “alert” (check your report’s legend). A value far outside the range: several times the upper limit or far below the lower one, not a few percent off. Any flag plus new symptoms that worry you.
• Discuss at your next visit. One or a few values a little outside the range while you feel well, such as cholesterol or vitamin D. A value that has changed a lot since your last test.
• No immediate concern. A value just outside the range with a likely reason, such as a hard workout before the test. Still mention it at your visit.

Not sure which group? Choose the more urgent one.

How labs handle truly dangerous results

Critical values are results so far from normal that they could be life-threatening without prompt treatment. Regulators require labs to have a critical value policy: the lab must alert the person who ordered the test straight away, usually your doctor rather than you. So a truly dangerous result rarely sits silently in a portal. Each lab sets its own list.

If you ordered the tests yourself

Ordering tests without a doctor changes who is watching your results.

• Find the “ordering provider” on your report. That is who the lab contacts about a critical value.
• If no one is named, call the lab about any value marked critical, and check that it has your phone number.
• Plan who will review the results. Nobody may follow up for you, so book a visit with a family doctor and bring the full report, with the lab’s ranges and units. They can decide whether you need a specialist.

Until that visit, the options further down this page can give you a first explanation and a list of questions to bring.

Why an H or L flag is not a diagnosis

Next to each value is a reference range. For most tests, it covers about 95% of results from healthy people, as Testing.com’s guide to reference ranges explains. So on any one test, 5 in 100 healthy people land outside it by chance.

With more tests, the odds add up: the JABFM paper works out that with 20 tests, 64.2% of healthy people will have at least one “abnormal” result. The real share is a little lower, because some results move together, but a flag or two is still very common.

One exception: a few tests, such as glucose, HbA1c (average blood sugar over 2–3 months) and cholesterol, use “limits at which decisions are made” rather than a 95% range. A flag there marks a threshold that matters for your health. You can look up any flagged marker in our lab test library.

Flags that are often harmless, but only a doctor can confirm

• Gilbert syndrome. An inherited condition that mildly raises bilirubin, a yellow pigment from worn-out red blood cells. A StatPearls review puts it at 4–16% of people, up to 20% in India, South Asia and the Middle East. It needs no treatment.
• Duffy-null associated neutrophil count. Many people of African ancestry have fewer neutrophils (the most common white blood cells) without more infections. A 2023 study in Blood Advances links this to a common blood-group variant called Duffy-null. A 2019 review describes the same in people of Middle Eastern and West Indian descent. The older name is “benign ethnic neutropenia.”

Both are diagnosed only after other causes are ruled out.

What may have skewed your result

The MedlinePlus guide to lab results lists food and drink, medicines and supplements, hard exercise and your period among things that can change results.

• Not fasting. Glucose and triglycerides (a type of blood fat) rise after a meal. If you were meant to fast and did not, tell your doctor.
• Hard exercise. In a 2008 weightlifting study, healthy men new to lifting trained for one hour. Their ALT and AST (liver enzymes) and CK (a muscle enzyme) stayed raised for at least 7 days.
• Too little fluid. Dehydration concentrates the blood. It is the most common cause of a high hematocrit (the share of blood made up of red cells). It can also raise hemoglobin (the oxygen carrier in red cells) and urea (a kidney waste product); see 8 ways patients accidentally distort their tests.
• Your period. It can shift some results; our guide to blood tests during your period explains which.
• Medicines and supplements. Biotin (vitamin B7), common in hair, skin and nail supplements, can cause “falsely high or falsely low results” in some tests, warns FDA guidance on biotin. Many thyroid hormone tests are affected. Tell your doctor everything you take, and do not stop a prescribed medicine on your own. On a GLP-1 drug such as Ozempic or Mounjaro, some results are expected to change; see which lab tests to monitor on GLP-1 drugs.

Read the report as a whole, not line by line

Doctors look for results that tell the same story. Each pattern below could point to something; only your doctor can say what it means for you.

• ALT and triglycerides up, glucose or HbA1c at the upper edge: a metabolic picture, such as fatty liver or insulin resistance (the body responding poorly to insulin).
• Normal hemoglobin but low ferritin (iron stores), perhaps with small red cells: iron stores can run low before hemoglobin falls.
• Creatinine, urea and hematocrit all slightly high: possibly just dehydration (creatinine is another kidney waste product); doctors often simply repeat the tests.
• High TSH and high LDL: an underactive thyroid (TSH is the hormone that drives it) can raise LDL, the “bad” cholesterol, so your doctor will likely check the thyroid first.
• ALT, AST and CK up after hard exercise: muscle, not necessarily the liver.

Our example report reads the first pattern as a whole. Its invented case is a 34-year-old woman with fatigue, slightly high ALT and triglycerides, and glucose and HbA1c at the upper edge. Line by line, nothing looks alarming. Together, the report reads them as an emerging metabolic syndrome (a cluster of risk factors for diabetes and heart disease) with signs of fatty liver. It ends with an action plan and questions for her doctor.

Compare with your earlier results

One result is a snapshot; a series shows a direction. A value can move a lot and still stay inside the range, and Testing.com notes that such a change “could mean something significant.” Creatinine, for example, can creep up for years without a flag.

• Line up your reports and compare each marker in the same units.
• Use the same lab when you can, as MedlinePlus advises for trends. Methods and ranges differ between labs; our piece on reference ranges online vs your lab explains why.
• Check the units. Glucose in mg/dL and in mmol/L looks very different; our unit converter switches between them.

In our experience, a value that has been slightly high and stable for years often matters less than one inside the range that has doubled.

Where to get your results explained before the appointment

Whichever you choose, aim to reach the appointment with the right questions, not a self-diagnosis. You can see a complete example report first; our comparison of Wizey and ChatGPT covers general chatbots.

Questions to take to your appointment

Write these down before the visit:

1. Which of my results matter, and which are not a concern?
2. Could anything have affected this result: food, exercise, my period, a medicine or a supplement?
3. Should we repeat the test? When, and at the same lab?
4. What do these results mean together with my symptoms and medicines?
5. How do they compare with my earlier results?
6. Do I need other tests to understand this?
7. What are the next steps, and who will follow up?
8. What should I watch for until then, and when should I call you?

Heard nothing after a few weeks? NHS guidance on blood tests says to contact the GP surgery or specialist; some surgeries only get in touch when they need to discuss results.

Before you upload your results anywhere

A lab report is sensitive health data. Before you upload it anywhere, ours included, check three things:

1. Who stores the file, and for how long?
2. Is it used to train AI models?
3. Can you delete it?

Before taking a photo, you can cover your name, address and ID number; keep the values, units and ranges visible. Wizey’s privacy documents are on our legal page.

Frequently asked questions

What do H and L mean on a blood test? H means your value is above the lab’s reference range; L means it is below. The range covers about 95% of healthy people, so a flag shows where your value sits, not what is wrong. The legend on your report explains other marks, such as critical values.

Is one slightly abnormal result a reason to worry? Usually not on its own. With 20 tests, about two in three healthy people have at least one value outside the range. What matters more is how far out it is, your symptoms, your other results and the trend. Mention it at your next visit.

My results are abnormal but nobody called me — is that bad? Not necessarily. Labs must alert whoever ordered the test about critical values, and some clinics only get in touch when action is needed. Silence can also mean that nobody has reviewed the results yet. If you hear nothing within a few weeks, or you ordered the test yourself, contact your clinic or the lab.

Should I repeat an abnormal test, and when? Your doctor decides. Mildly abnormal results are often repeated, especially if something could have skewed them, such as hard exercise, not fasting or dehydration. If you repeat a test, use the same lab and prepare the same way.

Can I get my blood test results explained online? Yes: through your clinic’s patient portal, an online doctor consultation, or an AI service such as Wizey, which reads your whole report and earlier ones together and prepares questions for your doctor. Check how each service stores your files. Decisions about tests and treatment stay with your doctor.

Conclusion

Most H and L flags are not emergencies. Check for symptoms and critical values first, then for anything that may have skewed a result. Read the report as a whole, compare it with earlier results and write down your questions.

If you want help with those steps for your own report, that is what we build Wizey for. It explains your results in plain language, shows how the markers relate, reads this year’s and earlier reports together and prepares questions for your doctor. The first analysis is free, and the example report shows what you get. It is not a substitute for a consultation, but a way to arrive at the appointment prepared.