The child may show symptoms such as fever, vomiting, or lethargy. It appears that he is suffering from a common illness, but these same signs may hide a serious infection that requires urgent medical intervention. Even when the results of the initial examinations are normal, they do not necessarily rule out the presence of a disease that requires treatment.
The difficulty of diagnosis increases in infants and younger children, due to their inability to describe what they feel or determine the location of the pain, in addition to the similarity of symptoms of different diseases, and the change in clinical and laboratory indicators as the condition develops.
How do doctors distinguish between diseases whose symptoms are similar? Why may initial tests fail to detect some diseases? When does re-evaluation become necessary?
Fever and vomiting…then cramps
A clinical case presented by Dr. Leila Ismaili, a pediatrician, illustrates how the diagnostic picture can change as symptoms develop and new test results appear.
The case involved a two-month-old baby girl, who began suffering from fever and diarrhea two days before seeing the doctor, and then other symptoms appeared, including vomiting and refusal to breastfeed.
The clinical examination showed a high temperature and signs of pain, in addition to indications of the beginning of dehydration.
The doctor presented several possibilities to explain the symptoms, including gastrointestinal infection, urinary tract infection, and meningitis.
According to Laila’s account, the results of the initial tests were inconclusive, as the complete blood count and the level of C-reactive protein (CRP), which is used to help detect infections, were within normal limits, and the urine culture result was negative.
The baby was monitored and treated for dehydration, but her fever returned and she developed convulsions, which necessitated a re-evaluation of her condition and additional tests.
New tests showed an elevated C-reactive protein level and an increased white blood cell count, and an examination of cerebrospinal fluid, obtained by lumbar puncture, helped diagnose her with meningitis.
The doctor said that the baby received appropriate treatment and her condition gradually improved until the symptoms disappeared.
This case highlights one of the challenges facing doctors, which is that symptoms and laboratory results may change as the disease develops, which makes monitoring and re-evaluating the condition an essential part of the diagnosis process.
Why are physical tests not enough?
Medical examinations depend on monitoring indicators related to the presence of the disease, but these indicators do not necessarily appear in all patients in the same way, and may be affected by the nature of the infection, the timing of taking the sample, and the stage the disease has reached.
For example, C-reactive protein and white blood cell counts are used to help evaluate the presence of inflammation or infection, but their results alone are not enough to confirm or rule out a particular disease.
The World Health Organization’s guidelines for the diagnosis and treatment of meningitis, issued in April 2025, stress that the results of blood tests, including white blood cell counts and C-reactive protein, cannot be relied upon alone to confirm or rule out bacterial meningitis.
The guidelines also stress the importance of examining the cerebrospinal fluid when the disease is suspected, whenever this is medically appropriate, and not delaying the examination based on the results of blood tests alone.
This does not mean that all children with fever need extensive tests or a lumbar puncture, but rather it confirms that the choice of tests depends on the child’s age, his general condition, the symptoms he suffers from, and the extent of suspicion of a serious infection.
These considerations are especially important in infants, as some serious infections may present with non-specific symptoms such as poor feeding, lethargy, or change in usual behavior.
The age of the child changes the method of diagnosis
Diseases do not appear in children in the same way at all ages, and their ability to express pain or describe symptoms varies.
An older child may be able to determine the location of the pain or explain the timing and nature of its appearance, while the infant does not have this ability, and often expresses his discomfort through crying or a change in the pattern of feeding, sleeping, and activity.
These changes may be the first signs that parents notice, but they do not alone determine the nature of the health problem.
Normal rates of heart rate, breathing, and other vital signs also vary with age, so measurements in an infant cannot be interpreted in the same way as with a school-age child.
Therefore, the diagnosis process depends on an integrated assessment that takes into account the age stage, the extent of the child’s response to the environment, the nature and development of symptoms, in addition to the results of clinical and laboratory examinations.
According to the guidelines of the British National Institute for Health and Care Excellence (NICE), an infant under 3 months old whose temperature rises to 38 degrees Celsius or more places him in a high-risk category for serious diseases and requires urgent medical evaluation.
The infant’s condition, precise age, and evaluation results determine the required examinations and therapeutic procedures, including the need for a lumbar puncture or antibiotic treatment.
What do parents’ comments add?
The diagnosis process is not limited to the symptoms that the doctor notices during the examination, but rather it usually begins with collecting information about the child’s health condition before the disease appeared, and the changes that have occurred in him.
Dr. Laila Ismaili explains that asking parents about sleep, breastfeeding, appetite, play, and activity level helps to understand the nature of these changes and link them to other symptoms.
A simple observation, such as a decrease in the number of feedings or a decrease in usual activity, may be important for the doctor when interpreting the rest of the data.
The medical history also includes knowing the timing of the onset of symptoms and the sequence of their appearance, previous diseases, medications that the child took, vaccination history, and any possible exposure to infection.
But obtaining this information may be more difficult when the child cannot express what he or she is feeling, or when feedback from family members varies.
The doctor faces another challenge during the examination, as fear or crying may cause some children to resist medical procedures, which affects the accuracy of some measurements.
Laila points out that examining the child while he is in the arms of one of his parents may sometimes help calm him down, and provide a better opportunity to observe his response and conduct a clinical examination.
Thus, parents’ observations become an important part of the evaluation, but they do not replace a medical examination or the necessary tests when there are indicators that require them.
113 children… and the reason remained unknown to 41
Diagnostic difficulties are not limited to acute cases whose symptoms develop within a short time, but also appear in children who suffer from a persistent fever whose cause is not clear despite the initial medical evaluation.
In a German study published on June 30, 2026 in the journal “Pediatric Molecular and Cellular Medicine,” scientists investigated the diagnostic value of basic and advanced examinations in children with fever of unknown cause.
The study included 113 children, whose case data were collected between May 2016 and December 2018, and their average age was 6.6 years.
The researchers required participation to record a temperature of 38.5 degrees Celsius or more during at least 5 days out of 10 consecutive days, and to find no clear cause for the fever after the usual medical evaluation.
The researchers were able to identify the disease causing the fever in 72 children, representing about 64% of the participants, while the cause remained undetermined in 41 children, representing about 36%.
Among the diagnosed cases, researchers recorded 26 cases of infection, 31 cases of systemic juvenile idiopathic arthritis, also known as Still’s disease, and 15 cases of other diseases that included inflammatory and immune disorders and malignant diseases.
The results showed that taking a medical history, clinical examination, and basic blood tests provided important indicators to guide the diagnosis, and medical imaging tests also helped detect additional signs in some patients.
These results do not mean that more than a third of children’s diseases are difficult to diagnose, because the study examined a selected group suffering from persistent fever of unknown cause, and did not include all children who see doctors due to high fever.
The study demonstrates the importance of following a gradual diagnostic approach, which begins with evaluating symptoms, medical history, and clinical examination, and then directs additional examinations according to the indicators that appear, instead of conducting extensive tests without a clear medical justification.
When do symptoms become a danger sign?
Although many childhood illnesses are mild, some symptoms require urgent evaluation, especially in infants and young children.
According to the guidelines of the British National Health Service (NHS), there are signs that should not be ignored, the most prominent of which are:
- The temperature of a child younger than 3 months rises to 38 degrees Celsius or more, which requires urgent medical evaluation.
- Convulsions, loss of consciousness, or difficulty waking the child up and responding to the environment.
- Difficulty or rapid breathing, or a change in the color of the lips and skin to blue or grey.
- The appearance of a rash that does not go away when pressed.
- Refusing breastfeeding or fluids, especially if accompanied by clear signs of dehydration, such as a decreased number of wet diapers or decreased urination.
Signs such as convulsions, difficulty breathing, and disturbance of consciousness require immediate emergency care. The return or worsening of symptoms after the first evaluation also requires recontacting the doctor, even if the results of previous tests were normal.
This does not mean that every fever is a sign of a serious illness, but rather that its interpretation must take into account the child’s age, general condition, accompanying symptoms, and changes that occur in him.
When does the doctor re-evaluate the diagnosis?
The doctor may begin the evaluation process with a set of possibilities, then eliminate or rearrange some of them as new information emerges. Changing the initial diagnosis does not necessarily mean that a medical error has occurred, as some diseases do not reveal all their signs in the early stages.
On the other hand, the continuation or deterioration of symptoms should not be considered normal just because previous examinations were reassuring. Therefore, the importance of medical follow-up and identifying signs that require a return to examination should not be neglected, as well as documenting the change in symptoms and laboratory results over time.
The diagnosis does not depend on a single analysis result or a separate symptom, but rather on linking the child’s age, medical history, clinical examination, test results, and the extent of the development of his condition. Timely re-evaluation may be the step that reveals a disease that was not apparent at the first examination.