Heat exhaustion is often a precursor to heat stroke or hyperthermia. One of the foremost ways of diagnosing heat exhaustion is to check the body temperature. Hyperthermia can be drug-induced or temperature-induced. In both cases, the body temperature rises and one suffers from high fever. However, this is not actually a fever but the beginning of a heat stroke. Rapidly rising body temperatures are a sure-shot sign of the onset of heat exhaustion. For confirmation of the diagnosis, the patient is administered with antipyretics (or fever reducing medicines). If fever reduces even partially, then heat exhaustion can be excluded from the diagnosis.

The blood is a complicated mixture and solution of solids, liquids and gases along with various kinds of cells. Blood tests are done to determine the concentrations of blood gases and the levels of sodium and potassium. Sodium and potassium are important electrolytes that maintain pressure in the cells. Increased levels of these ions is an indicator of heat exhaustion. This is often obtained from the baseline metabolic profile of a person. The serum electrolytes show abnormal concentrations due to volume depletion. Similarly, reduced partial pressure of the blood gases also indicates heat exhaustion.

Heat exhaustion often leads to rhabdomylosis. This is the condition in which the muscle tissues break down and the muscle fiber contents are released into the blood stream. The main constituent is myoglobin, which is harmful for the kidneys and can also lead to kidney dysfunction. The baseline creatine kinase test is done and followed up for the next 48 hours to diagnose this rhabdomylosis. The levels of creatine kinase correlates directly with the extent of damage to the muscle tissues. In times of heat exhaustion, the creatine kinase levels go above 1,00,000 units per ml. 

When baseline renal function tests are conducted, one will find elevated levels of creatinine and blood urea in cases of heat exhaustion. These tests have to be repeated and followed up for up to 48 hours to obtain conclusive results. Since the constituents of the urine increase in concentration, urine becomes darker in its color. This is one of the easiest ways to diagnose a suspected heat exhaustion. The patient can himself/herself see the color of the urine getting darker. This also means that the kidney function is getting affected as it often happens in heat related conditions. At such times, myoglobinurea, the result of rhabdomylosis, is also found in the urine.

A chest X-Ray is often done as part of the diagnosis to distinguish between heat exhaustion and pulmonary causes. Pulmonary edema brings on symptoms similar to that of heat exhaustion but it also manifests as a later complication of a heat stroke. In order to distinguish between the two, a chest X-ray is ordered. The X-ray also help in evaluating the damage to internal organs.

Some drugs (e.g., cocaine, salicylates, phencyclidines) produce excessive internal heat. Many psychotropic medications, illicit drugs and anesthetic agents at times cause hyperthermia. Treatment for heat exhaustion varies depending on the cause. A medicine screen or toxicology screen is often used to determine whether the cause is medicines or drugs. The positive toxicology screen rules out external heat and lack of sweating as the causes of heat exhaustion.

The body exhibits a host of signs and signals when the onset of heat exhaustion is near. A dry skin with pronounced dryness at the lips is one important signal. The patient starts to exhibit a confused state of mind and responses are nonsensical at times. Frequent vomiting along with the other physical signs is often confirmatory of heat exhaustion.