Subfebrile temperature

What does subfebrile temperature mean? The Latin prefix sub means "under, near" (remember words like submarine, offal, or subtropics). And febris means "fever" in Latin. So, literally, subfebrile temperature is defined as "near feverish."

The human body temperature is a complex indicator of the thermal, i.e. thermal state of the organism. The mechanism of our thermoregulation is “automatically” set to the normal value of +36.6°C and allows its physiological changes within plus or minus 0.5-1°C. The general temperature range is 36-39°C. When the thermometer rises to +38-39°C, doctors talk about a febrile temperature, and above +39°C – about a pyretic temperature. And what is a subfebrile temperature?

The classic subfebrile body temperature is +37-37.5°C, but experts indicate a higher figure - 37.5-38°C. So, it is quite reasonable that a subfebrile temperature of 37 degrees and up to +38°C is considered "near-feverish" by most domestic doctors, while their Western colleagues consider a temperature of 99.5-100.9°F or 37.5-38.3°C to be such.

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Causes of subfebrile temperature

The causes of subfebrile temperature, as well as febrile and pyretic, are associated with changes in the functioning of the limbic-hypothalamic-reticular system of the body. Simply put, temperature is regulated in the hypothalamus, which works as a thermostat. Endogenous or exogenous pyrogens cause the release of prostaglandins (inflammatory mediators), and they act on the neurons responsible for thermoregulation, which are located in the hypothalamus. And the hypothalamus generates a systemic response, and as a result, the body is given a new temperature level.

In what diseases is subfebrile temperature observed for a certain period of time? The list of such diseases is quite extensive and includes:

• infectious diseases - influenza, acute respiratory viral infections, tuberculosis, typhoid, brucellosis, malaria, ornithosis, mononucleosis, Epstein-Barr herpesvirus, cytomegalovirus, rotavirus gastroenteritis and gastroenterocolitis, tick-borne borreliosis (Lyme disease), HIV, urogenital infections, etc.;
• parasitic diseases (helminthic infestations, giardiasis, leishmaniasis, toxoplasmosis);
• sluggish inflammatory processes in chronic rhinitis, sinusitis, sinusitis or tonsillitis; in inflammation of soft tissues (boils, abscesses); in focal pneumonia and lung abscess; in chronic cholecystitis, pancreatitis, cystitis, prostatitis, pyelonephritis, etc.;
• thyroid dysfunction (initial stages of hyperthyroidism, hypothyroidism, thyrotoxicosis);
• systemic immunological diseases - systemic lupus erythematosus, sarcoidosis, giant cell temporal arteritis (Horton's disease), rheumatoid arthritis, granulomatous enteritis (Crohn's disease), Wegener's granulomatosis, Bechterew's disease, Sjögren's syndrome;
• tissue necrosis, which can occur as a result of the destruction of red blood cells (hemolysis) during cerebral hemorrhage, myocardial infarction, after surgery, with compression syndrome, etc.;
• allergic reactions of various etiologies;
• metabolic disorders (gout, porphyria, etc.);
• thromboembolic processes (deep vein thrombosis, pulmonary embolism, etc.).

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Signs of subfebrile temperature

Subfebrile body temperature accompanies a number of diseases, sometimes being, in fact, their only symptom, recorded at the initial stage of development. Apart from elevated temperature, this condition may not manifest itself in any other signs, which is a potential threat to health.

So the key signs of subfebrile temperature are periodic or permanent (constant), short-term or long-term increase in temperature to +37-38°C.

Subfebrile temperature as a symptom

Subfebrile temperature is a sign of a particular pathology. Subfebrile temperature and cough, subfebrile temperature and headache, as well as weakness and subfebrile temperature are typical symptoms of not only acute respiratory viral infections or flu, but also focal pneumonia and pulmonary tuberculosis. In particular, with focal or infiltrative tuberculosis, subfebrile temperature is observed in the evenings, which rises for 3-4 hours to +37.3-37.5°C.

Often, subfebrile temperature after ARVI is the result of incomplete recovery, weakened immunity or the effects of medications.

In most cases, subfebrile temperature during bronchitis will not rise above +37.7°C, subfebrile temperature after pneumonia is approximately in the same range. Often, doctors cannot determine the exact cause of this phenomenon and call it post-infectious subfebrile temperature.

The characteristic subfebrile temperature in tonsillitis is 37-37.5°C, and the subfebrile temperature after tonsillitis can remain at the same level for one to two weeks. A longer subfebrile temperature should be alarming, because, as is known, tonsillitis quickly becomes chronic decompensated, and streptococcal infection in frequent tonsillitis has a pathological effect by intoxicating the heart tissue, causing infective endocarditis, and affecting the kidneys, leading to glomerulonephritis.

Subfebrile temperature in cystitis, along with other symptoms of this disease, passes after appropriate drug therapy. However, when subfebrile temperature up to 37.5-37.8°C persists after the end of treatment, then there are good reasons to assume that the inflammation from the bladder has spread to the kidneys and threatens pyelonephritis.

Subfebrile temperature after tooth extraction, as well as subfebrile temperature after surgery performed on any tissues and organs, may have a separate list of causes, among which the first place is the body's reaction to the damaging factor and infection (for example, infectious blood poisoning - pyemia). Drugs taken both before and after surgery also make their contribution.

Subfebrile temperature in oncology is most often observed in myelo- and lymphocytic leukemia, lymphomas, lymphosarcoma and cancerous kidney damage. As oncologists note, prolonged subfebrile temperature - for six months or even more - is one of the symptoms of the early stages of these diseases. Also, for oncological patients after radiation and chemotherapy, neutropenic subfebrile temperature is characteristic, associated with a weakened immune system.

Nausea and subfebrile temperature will suggest intestinal dysbacteriosis to a gastroenterologist. But subfebrile temperature at night usually drops to a physiologically normal level or slightly lower, although it can persist, for example, with a latent herpes virus infection, inflammation of the bile ducts or hepatitis C.

It should be borne in mind that a constant subfebrile temperature that remains above normal throughout the day and fluctuates during the day by more than one degree is a symptom of infective endocarditis. A prolonged subfebrile temperature that appears every 24-48 hours is a typical manifestation of malarial plasmodium.

The human immunodeficiency virus acts slowly, so a subfebrile temperature in HIV, in the absence of other signs in carriers of this infection, is an indicator of a total decrease in the body's defenses. The next stage can be the defeat of the body by any infection with the development of many immune-mediated diseases.

Low-grade fever with VSD

Thermoregulation of the body - as the activity of all internal organs, secretory glands and vessels - is coordinated by the autonomic nervous system, which ensures the stability of the internal environment and adaptive reactions of the body. Therefore, disturbances in its work can manifest as subfebrile temperature with VSD, that is, vegetative-vascular dystonia.

In addition to a spontaneous daytime increase in temperature to 37-37.3°C, there may be neurocirculatory disorders such as changes in blood pressure and pulse rate, decreased muscle tone, and hyperhidrosis (increased sweating).

Depending on the cause of VDS, clinical medicine distinguishes between genetic, infectious-allergic, traumatic and psychogenic vascular dystonia.

Until recently, an increase in temperature in such conditions, i.e. without an obvious cause, was defined as a subfebrile temperature of unclear etiology. It is now known that there is a violation of the thermoregulation process due to diencephalic syndrome - a congenital or acquired dysfunction of the hypothalamus (our main "thermostat").

Congenital causes of this pathology include functional somatic disorders such as VSD, and acquired causes include cerebrovascular accidents in the hypothalamus area, traumatic brain injury, encephalitis, intoxication, etc.

Anemia and subfebrile temperature

Anemia and subfebrile temperature are closely related to each other at the biochemical level. Iron deficiency anemia leads to a disruption in the production of hemoglobin and a decrease in its content in erythrocytes, which carry oxygen to the cells. And with a lack of oxygen in all cells of the body and, first of all, in the brain, the metabolic process is disrupted. Therefore - in addition to all other signs of iron deficiency in the body - a slight increase in body temperature is quite often observed. Children and adolescents during puberty are most prone to iron deficiency anemia. In addition to subfebrile temperature, they often have colds, appetite and body weight may decrease.

In addition, poor absorption of iron is associated with a lack of vitamin B9 (folic acid) and vitamin B12 (cyanocobalamin), which regulate the synthesis of hemoglobin in the bone marrow. And such anemia is called pernicious.

Precision anemia and subfebrile temperature - if ignored - can lead to the development of inflammation and atrophy of the gastrointestinal mucosa.

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Subfebrile temperature in women

Subfebrile temperature before menstruation in women refers to physiological periodic changes in thermoregulation (within 0.5 degrees) and is associated with an increased flow of estrogen and estradiol and their metabolic products into the blood: hydroxyestrones, etiocholanolone, methoxyestradiol, etc.

Subfebrile temperature during pregnancy (up to +37.5°C) can be observed in the early stages, in the first 12 weeks – due to an increase in the level of progesterone produced by the corpus luteum of the ovaries and its effect on the hypothalamus. Later, temperature indicators normalize.

However, a slight but constant subfebrile temperature in pregnant women is quite possible when, against the background of a natural decrease in immunity, vague symptoms of so-called TORCH infections appear: toxoplasmosis, hepatitis B, varicella-zoster virus, rubella, cytomegalovirus and herpes simplex virus. Since all these infections can cause congenital pathologies of the fetus, it is important to be vigilant in time with a subfebrile temperature and take a blood test for TORCH infections.

And finally, subfebrile temperature in women very often occurs during menopause, and this is again associated with changes in their hormonal background.

Subfebrile temperature in a child

Thermoregulation disorders detected in childhood in at least 2% of cases represent congenital diencephalic syndrome, that is, problems with the hypothalamus, which was discussed above.

Subfebrile temperature in a child often accompanies infections of the upper respiratory tract, nasopharynx and ears. Thus, subfebrile temperature and cough can be with acute respiratory viral infections, chronic tonsillitis, bronchitis, pneumonia. Temperature is caused by teething and vaccinations. Subfebrile temperature can be provoked by physical activity, strong excitement, overheating when wearing heavy clothes, anemia, etc.

Subfebrile temperature in a teenager is associated with the period of sexual development, but possible pathologies cannot be ignored. In addition to those listed above (see the section Causes of subfebrile temperature), pediatricians pay special attention to childhood and adolescent thermoneurosis, which is caused by diencephalic syndrome, malignant blood diseases, thyroid pathologies, and autoimmune diseases. For example, children under 16 years of age may develop Still's disease or systemic juvenile idiopathic arthritis, which is characterized by weakness and subfebrile temperature.

It can also be a side effect of long-term use of certain medications, such as atropine, diuretics, anticonvulsants, antipsychotics and antibacterials. Thus, subfebrile temperature with antibiotics occurs because their use erases the signs of some diseases, and then only one symptom remains - an increase in thermometer readings.

Tests for subfebrile temperature

Doctors acknowledge the fact that making a correct diagnosis with a subfebrile temperature is not an easy task. Therefore, it is necessary to pass all tests with a subfebrile temperature:

• general blood test;
• blood tests for RW, HIV, viral hepatitis B and C;
• blood test for TORCH infections;
• blood test for rheumatoid factor;
• blood test for thyroid hormones;
• blood test for tumor markers;
• general urine analysis;
• sputum culture for tuberculosis.

In addition to tests, X-rays or ultrasound may be prescribed.

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Treatment of subfebrile temperature

How to bring down a subfebrile temperature? For your information, in this situation only an incompetent medical worker will immediately - without examination - prescribe antipyretic drugs. And you should not take aspirin, acetaminophen or ibuprofen on your own either, especially in cases where the subfebrile temperature has been observed for 2 months or the subfebrile temperature has been maintained for more than a year or longer.

What to do with a subfebrile temperature? Seek medical help from competent doctors. If there are no other symptoms and no complaints of deterioration in health, then treatment of subfebrile temperature is not required. Therapy of these conditions is extremely difficult, especially when doctors diagnose subfebrile temperature of unclear etiology.

A hundred years ago, the old name for subfebrile conditions was used - "general malaise", in which it was recommended to eat better, walk more in the fresh air and not to be nervous. And what do you think, it actually helped many people...

Today, it is necessary to carry out etiological treatment of subfebrile temperature, and what it will be depends on the pathogenesis of the disease.

If subfebrile temperature appears frequently or is constant, if it worries you (especially when “nothing hurts anywhere”), consult a doctor.

If you have a long-lasting low-grade fever, weakened immunity or chronic diseases, consult a doctor without delay.