Lab results
Why your dietitian should read your lab results
Your blood work shows how your body is handling food, so a dietitian who reads it can aim your eating plan at what matters for you. Your doctor diagnoses and treats. The dietitian turns the numbers into plain language and a plan you can follow.
Clinically reviewed by Dr. Ambily Kushal, RD, MS, PhD · Published · Last reviewed
Why should a dietitian read your lab results?
Labs show what is happening inside your body, which general advice cannot. A dietitian who reads them can pick the changes that fit you and skip the ones that do not.
Two people can both say they want to eat better and need very different plans. One has blood sugar that runs high after meals. Another has low stored iron. A third has a liver enzyme that came back raised. The same advice would not serve all three.
Doctor visits are often short, and results can sit in a portal without much discussion of food. A dietitian visit gives you time to ask what each number means for your meals.
Reading labs does not mean diagnosing. It means using the information your doctor already collected to make food advice more specific.
Which common labs relate to nutrition?
Blood sugar markers, cholesterol, liver enzymes, thyroid tests, vitamin D, B12, iron stores and kidney function all connect to food in some way. Each one measures something specific.
A1c and fasting glucose
A1c reflects your average blood sugar over about the past 3 months. Anemia and some kidney or liver conditions can make A1c less accurate, so your doctor may use other tests. In the ranges used by NIDDK, an A1c below 5.7 is normal, 5.7 to 6.4 falls in the prediabetes range and 6.5 or above falls in the diabetes range. Your doctor makes the diagnosis, often confirming it with a second test.
Fasting glucose is a snapshot of blood sugar after a night without food. The two tests answer different questions: A1c shows the pattern, and fasting glucose shows one moment. A dietitian uses both to see how meals, timing and activity are playing out.
Lipids: cholesterol and triglycerides
A lipid panel reports total cholesterol, LDL, HDL and triglycerides. Food choices, body weight, activity, alcohol and genetics all influence these numbers. Fiber, fats and sugary drinks are common places to look in an eating plan.
Whether you need to fast before the test depends on what your doctor orders. Ask when you book.
Liver enzymes
ALT and AST are enzymes made mainly in the liver. They can run high for many reasons, including fatty liver, alcohol, medicines and viral illness. A dietitian does not decide the cause. The doctor does. What the dietitian can do is build an eating plan that supports the liver once your doctor has a diagnosis.
Thyroid tests
TSH is a hormone from the pituitary gland that signals the thyroid. TSH rises when thyroid hormone is low and falls when it is high, so it is a first check of thyroid function, not a reason for a problem. Thyroid status can affect energy, weight and digestion, so a dietitian wants to know the result and whether you take a thyroid medicine.
Vitamin D
Most vitamin D blood tests measure a form called 25(OH)D. MedlinePlus notes that routine testing is not recommended for everyone, so this one is usually ordered for a reason, such as bone health or a condition that affects absorption. If a level is low, your dietitian and doctor decide together how to respond, including whether a supplement makes sense.
B12
B12 comes mostly from animal foods. People who eat few or none, older adults, and people with absorption problems or certain medicines may run low. A dietitian looks at your usual meals and, with your doctor, decides whether food changes or a supplement fit your situation.
Iron and ferritin
Ferritin shows how much iron your body has stored. Low iron stores are common and have several possible causes, so your doctor looks into why. Your dietitian can review iron-rich foods and what helps or blocks absorption at meals.
Kidney function
An estimated GFR, calculated from a creatinine blood test, tells you how well the kidneys filter. It matters for nutrition because protein, salt, potassium and phosphorus advice can change when kidney function is lower. If your eGFR is low, check with your doctor before any big change in protein or supplements, and share the result with your dietitian.
Why do trends matter more than one number?
One result is a snapshot, and many things can move it for a day or two. Two or three results over months show direction, which is what an eating plan can respond to.
A single reading can shift with a recent illness, a poor night of sleep, a hard workout, a missed meal or a different lab. A number just outside the usual range may mean very little on its own.
When a dietitian sees several results over time, the questions get sharper. Is the A1c edging up or settling? Did the triglycerides change after you cut back on sugary drinks? Did ferritin move after a few months of different meals?
- Bring older results too, not only the newest one.
- Write down changes you made between tests, such as new meals, a new medicine or a stressful month.
- Ask your lab or portal to show results side by side if it can.
What stays with your doctor?
Diagnosis, ordering and interpreting tests for disease, and every medicine decision stay with your doctor. The dietitian builds the eating plan alongside that care.
See your doctor first, before a diet change, if you have chest pain, fainting, black or bloody stools, yellowing of the skin or eyes, or a result your doctor has called urgent.
Your doctor
- Diagnoses conditions and decides which tests to order
- Starts, changes or stops medicines
- Investigates results that are far out of range
- Decides whether a supplement is safe with your medicines
Your dietitian
- Explains what a result means for daily eating
- Builds a plan around your schedule, tastes and culture
- Tracks how food changes line up with later results
- Suggests which labs to discuss with your doctor
How do you prepare for a visit about your labs?
Gather your recent reports, a list of medicines and a few questions for your dietitian. A short written list makes the visit far more useful.
If you do not have recent labs, say so. Your dietitian can suggest what to ask your doctor about, and you can bring the results to a follow-up visit.
- Download full lab reports from your patient portal, with the reference ranges printed.
- Collect results from the past year or two if you have them.
- List your medicines and any supplements, and tell your dietitian about each one.
- Note symptoms, such as tiredness, bloating or cramps, and when they happen.
- Write down your usual meals for a normal week, not an ideal one.
- Bring two or three questions you want answered in plain words.
What does a dietitian do with your results?
A dietitian links each result to your meals, habits and symptoms, then picks a few changes to try first. The goal is a plan that fits your life and that a later lab can test.
Say your A1c sits in the prediabetes range and your triglycerides are high. A dietitian will look at when you eat, what you drink, how much fiber is on your plate and how you move. Those patterns often explain more than any single food.
The same approach applies to other results. A low ferritin leads to questions about meals, periods, medicines and digestion. A raised liver enzyme leads to questions about alcohol, sugary drinks and weight. The numbers point to questions, and your history supplies the answers.
Good dietitians also explain why. When you understand how a result and your food connect, it is easier to keep going on a busy week.
- Translate each result into plain words.
- Choose two or three changes, not twenty.
- Agree on which results to recheck, and when, with your doctor.
- Pass questions back to your doctor when a result needs medical follow-up.
How often should you recheck labs?
There is no single schedule. Your doctor sets the timing based on the test, your results and your health, and your dietitian can suggest when a recheck would show something useful.
Some markers move slowly. A1c reflects about 3 months, so checking it every few weeks tells you little. Others, such as a lipid panel after a major change in eating, may be rechecked on a different schedule.
A good rhythm is simple. Make a plan, give it enough time to show up in your body, then recheck what your doctor orders. Your dietitian can then compare the new result with the old one and adjust meals.
Bring your last two or three reports to a first visit ($140, self-pay) and ask which number is worth rechecking first.
What patients say about this kind of care
One patient valued clear advice and resources based on science, tailored to their needs and progress.
“Dr. Ambily provides clear advice and resources based on science. She tailored her guidance based on my needs and progress.”
One patient described having complex bloodwork translated into plain language that was easy to understand.
“She translated complex bloodwork and clearly explained what it revealed about my overall health in a way that's easy to understand”
One patient left a first visit with an action plan, additional lab work and a follow-up in 6 weeks.
“recommended a great action plan, additional lab work, and follow-up in 6 weeks.”
One patient said that having the science broken down helped them understand how one thing affects the other.
“She took time to break down the science of it all. I can now understand how one thing affects the other.”
One patient described having everything broken down so they could understand their nutritional needs.
“She explained everything and broke it down so I could understand my nutritional needs.”
One patient described evidence-based guidance with personalized recommendations tailored to their needs.
“She provides thoughtful, evidence-based guidance and personalized recommendations tailored to my needs.”
Excerpts from patient reviews of Dr. Ambily Kushal, quoted word for word. Each describes one person’s care; individual experiences vary and are not a promise of results.
Frequently asked questions
Can a dietitian order lab tests?
Ordering usually goes through your doctor. A dietitian can suggest which results are worth asking your doctor about and help you understand them once you have them.
Can a dietitian tell me what my lab result means?
A dietitian can explain what a test measures and how food and habits relate to it. Whether a result points to a condition is a diagnosis, and that stays with your doctor.
Do I need blood work before my first visit?
No. Recent results help, but you can start without them. Your dietitian can suggest what to discuss with your doctor and review the results at a later visit.
What if my results are in the normal range?
Normal results still help. They show what is going well, and they give a baseline for comparison later. Symptoms and eating habits matter too, so a normal panel does not close the conversation.
Should I take a supplement if my doctor says a result was low?
Talk with your doctor and dietitian first. The cause of a low result matters, and your doctor can tell you whether a supplement interacts with your medicines or is needed once the cause is found.
Which labs should I bring to a dietitian?
Bring anything recent: A1c or glucose, a lipid panel, liver enzymes, thyroid tests, vitamin D, B12, iron and ferritin, and kidney function. Bring what you have rather than waiting for a full set.
Sources
- The A1C Test and Diabetes (National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK))
- Cholesterol Levels (MedlinePlus, National Library of Medicine)
- Liver Function Tests (MedlinePlus, National Library of Medicine)
- TSH (Thyroid-Stimulating Hormone) Test (MedlinePlus, National Library of Medicine)
- Vitamin D Test (MedlinePlus, National Library of Medicine)
- Ferritin Blood Test (MedlinePlus, National Library of Medicine)
- Estimated Glomerular Filtration Rate (eGFR) and GFR Tests (MedlinePlus, National Library of Medicine)
- Vitamin B12: Fact Sheet for Consumers (NIH Office of Dietary Supplements)
Related reading
Our condition guides are general education, not medical advice. Talk with your doctor about your own diagnosis, tests and medicines.