Constant fatigue and what tests will help find its cause

Chronic fatigue is not the same as normal fatigue after a working day. It does not disappear after a night's sleep, can occur without obvious stress and significantly limits daily activity: it interferes with work, study, concentration and performing routine tasks. Often a person wakes up already exhausted, feels muscle weakness, drowsiness, dizziness or a state of "fog" in the head.

According to MedlinePlus, fatigue is a feeling of exhaustion, lack of energy, or general weakness. If it doesn’t go away after getting enough sleep, eating a balanced diet, or reducing stress, it’s a reason to see a doctor. The causes can be varied: infections, chronic diseases, medication side effects, pain syndromes, depressive disorders, and more.

That is why persistent fatigue should not be explained solely by overload or character traits. It is often caused by laboratory-confirmed disorders: anemia, iron deficiency, vitamin B12 deficiency, thyroid dysfunction, glucose fluctuations, chronic inflammation, liver or kidney pathologies.

First, it's worth understanding what fatigue is.

For a doctor, it is not only important that a person gets tired. The nature of the fatigue is important. One situation is when a person wants to sleep after several nights without rest. Another is when they sleep enough, but still have no strength. Another is when fatigue appears after an infection, accompanied by fever, weight loss, palpitations or shortness of breath.

Before the examination, you should pay attention to:

• when fatigue began;
• was there a previous infection?;
• Does it go away after sleep?;
• Is there shortness of breath during exertion?;
• Is there dizziness?;
• is there a heartbeat;
• Has your weight changed?;
• Are your hands and feet cold?;
• is there thirst and frequent urination;
• Is there pain in the joints or muscles?;
• are there heavy menstruation;
• whether the person is taking new medications;
• Are there any chronic diseases?.

Such details help you not to take tests haphazardly, but to choose the right direction for the test.

When the cause may be anemia

Anemia is one of the common causes of constant fatigue. If there is not enough hemoglobin or red blood cells, the tissues receive less oxygen. Because of this, the usual load begins to exhaust faster, weakness, dizziness, shortness of breath, palpitations, pallor, cold hands and feet appear.

The NHLBI notes that iron deficiency anemia can cause fatigue, shortness of breath, chest pain, headache, restless legs syndrome, and other symptoms, and undiagnosed or untreated anemia can lead to complications.

You should think about anemia if fatigue is combined with the following symptoms:

• pallor;
• shortness of breath when climbing stairs;
• palpitation;
• dizziness;
• brittle nails;
• hair loss;
• coldness in the extremities;
• heavy menstruation;
• weakness after light exertion;
• low ferritin in previous tests.

In such a situation, it may be appropriate to anemia test, which helps assess not only hemoglobin, but also possible deficiencies behind weakness.

When fatigue is related to iron stores

Sometimes hemoglobin is still within normal limits, but iron stores are already low. A person may experience fatigue, hair loss, brittle nails, decreased endurance, headaches, or chills. In such cases, it is important to evaluate not only a complete blood count, but also ferritin and other indicators of iron metabolism.

Ferritin helps to understand how much iron the body has in reserve. If it is low, the cause of fatigue may be related to iron deficiency or anemia, which is why patients often seek, Why are my hands and feet cold and what tests should I take?..

It is especially important to check your iron levels if you have:

• heavy or prolonged menstruation;
• limited nutrition;
• frequent diets;
• pregnancy or postpartum period;
• chronic intestinal diseases;
• blood in the stool;
• frequent blood donation;
• prolonged weakness for no apparent reason.

When to check vitamin B12

Vitamin B12 deficiency can manifest itself not only in anemia. It can affect the nervous system, so fatigue is sometimes accompanied by numbness, tingling in the hands and feet, unsteadiness of gait, weakness, and impaired memory or concentration.

MedlinePlus notes that a B12 deficiency can cause fatigue, lack of energy, dizziness, and numbness and tingling in the hands and feet. Long-term deficiency can lead to nerve damage, so symptoms should not be ignored.

A B12 test may be appropriate if there is:

• constant weakness;
• numbness or tingling;
• burning tongue;
• disequilibrium;
• memory problems;
• restrictions on animal products;
• chronic diseases of the stomach or intestines;
• taking medications that may affect absorption;
• anemia of unknown origin.

In such cases, the doctor may prescribe B12, folic acid, a complete blood count, and additional tests depending on the symptoms.

When fatigue can be a sign of hypothyroidism

The thyroid gland affects metabolism, body temperature, heart function, nervous system, skin, hair, and muscles. When its function is reduced, a person may feel not just tired, but generally "slowed down.".

The American Thyroid Association notes that people with hypothyroidism may experience fatigue, chills, weight gain, dry skin, hair loss, constipation, and other symptoms.

The following may indicate the benefit of checking the thyroid gland:

• drowsiness;
• frostbite;
• weight gain for no apparent reason;
• dry skin;
• hair loss;
• puffiness;
• constipation;
• menstrual cycle disorders;
• decreased mood;
• slow heartbeat.

If fatigue is combined with such manifestations, it is worth evaluating TSH and free T4. You can read more about the meaning of the result in the material about elevated TSH.

When to check glucose

Carbohydrate metabolism disorders can also manifest as fatigue. With elevated glucose levels, the body does not always use energy efficiently, and along with this, thirst, frequent urination, hunger, blurred vision, slow wound healing, or frequent infections may occur.

The CDC lists frequent urination, increased thirst and hunger, fatigue, blurred vision, unintentional weight loss, and frequent infections as symptoms of diabetes.

Glucose and glycated hemoglobin should be discussed with a doctor if fatigue is combined with:

• severe thirst;
• frequent urination;
• night trips to the toilet;
• blurred vision;
• dry mouth;
• slow healing of wounds;
• frequent fungal or urinary infections;
• a family history of diabetes;
• weight gain or sudden weight loss.

Glycated hemoglobin helps estimate average glucose levels over the previous months, so it is often used in conjunction with blood glucose.

When fatigue may be caused by inflammation or infection

After an acute infection, weakness may persist for some time. However, if fatigue persists for a long time, is accompanied by fever, night sweats, swollen lymph nodes, joint pain, rash, or weight loss, a closer evaluation is needed.

MedlinePlus notes that possible causes of fatigue include infections that take a long time to treat or from which the body does not recover immediately, including mononucleosis, hepatitis, tuberculosis, HIV, and other conditions.

In such a situation, the doctor may prescribe:

• complete blood count with leukocyte formula;
• C-reactive protein;
• ESR;
• liver tests;
• tests for specific infections as indicated;
• urine analysis;
• additional examinations depending on symptoms.

If fatigue develops after COVID-19 and persists for months, it's also important to assess your overall health. The CDC notes that Long COVID can include fatigue, feeling worse after exercise, brain fog, and many other symptoms that can last for months or years.

When to evaluate the liver and kidneys

The liver and kidneys are involved in detoxification, metabolism, water-salt balance, and many other processes that affect your well-being. Their dysfunction doesn't always start with pain. Sometimes the first symptoms are weakness, decreased endurance, swelling, urine discoloration, itching, nausea, or loss of appetite.

The NIDDK notes that early stages of chronic kidney disease often have no symptoms, and many people don't notice symptoms until later stages. Blood and urine tests are used to diagnose the condition.

MedlinePlus describes fatigue as a possible symptom of liver disease, and also indicates that liver disease can cause jaundice, changes in urine and stool color, swelling, and easy bruising.

For verification you may need:

• creatinine;
• estimated glomerular filtration rate;
• urea;
• general urine analysis;
• ALT;
• AST;
• bilirubin;
• alkaline phosphatase;
• GGT;
• albumin;
• electrolytes.

These tests are especially appropriate if fatigue is accompanied by swelling, changes in urine, itching, a yellowish tinge to the skin, and pain or heaviness in the right upper quadrant.

What tests can help find the cause of fatigue?

This list doesn't mean that you should get all the tests done at once. It shows what your doctor might look for if your fatigue is persistent and has no obvious explanation.

When fatigue requires a faster consultation

Most cases of fatigue are not urgent. But there are combinations of symptoms that are best not to be put off.

See a doctor as soon as possible if you have:

• sudden or increasing weakness;
• dyspnea;
• chest pain;
• faint;
• palpitation;
• black stools or bleeding;
• high temperature;
• night sweats;
• weight loss for no reason;
• enlarged lymph nodes;
• pronounced pallor;
• severe thirst and frequent urination;
• swelling;
• yellowish tinge to the skin or eyes;
• confusion of consciousness;
• fatigue after an infection that does not subside for weeks.

In such cases, tests are needed not for reassurance, but to find a cause that may require treatment.

How to prepare for the inspection

Preparation depends on the specific tests. If you are planning to test your glucose, biochemical parameters, or certain hormones, your doctor or laboratory may recommend that you donate blood in the morning or on an empty stomach.

Before the examination, it is useful to:

• write down the main symptoms;
• note when fatigue began;
• remember past infections;
• prepare a list of medications and supplements;
• report heavy menstruation;
• talk about diets or dietary restrictions;
• take preliminary tests;
• Do not start taking iron, B12, iodine, or hormonal medications on your own before consulting.

If a person is already taking supplements, it is important to inform the doctor. Some of them can affect test results or make interpretation difficult.

What not to do when you are constantly tired

Constant fatigue often makes you look for a quick solution. But there is no universal pill for fatigue, because the causes can be different.

You should not do it yourself:

• take iron without a confirmed deficiency;
• start thyroid hormones;
• taking high doses of B12 or folic acid without a plan;
• blame everything solely on stress;
• ignore shortness of breath, weight loss, fever, or bleeding;
• take dozens of tests without understanding the purpose;
• treat one indicator without a diagnosis;
• Postpone the consultation if fatigue worsens.

If fatigue lasts for weeks, doesn't go away after sleep, and interferes with your work and life, don't ignore it. This is not the norm, but a reason to talk to your doctor. Start simple: record your symptoms, remember when it all started, and seek help. Your doctor will help you determine what tests are really needed so you don't have to do unnecessary tests, but also don't miss the important ones. Fatigue can be caused by anemia, deficiencies, hormonal changes, problems with glucose, liver, kidneys, or inflammation. And for almost every one of these reasons, there is a treatment or correction that can restore your energy. The main thing is to take the first step.

Author: Ulyana Anatolyivna Dzyuba

Director of Medi Lab Plus LLC, a doctor of the highest category. Has over 45 years of practical experience in medicine and laboratory diagnostics. Founder and head of the laboratory since 2007. More details…