The diagnosis of thyroid storm is a clinical one. The clinical state resembles that of a hyperadrenergic state.  There is no cut off for thyroid hormone levels which defines thyroid storm or differentiates it from severe thyrotoxicosis.

The scoring system (below) can be used to aid diagnosis but if a patient exhibits signs of severe thyrotoxicosis it is safer to assume that thyroid storm may be imminent and manage the patient aggressively.

Scoring system for thyroid crisis by Burch and Wartofsky [4]

This uses a numerical score to predict the presence of thyroid storm with categories of unlikely, impending and diagnostic. Five features are assessed to give an overall score:

Thermoregulatory dysfunction

Temperature oC

37-37.7 5
37.7-38.3 10
38.3-38.8 15
38.8-39.4 20
39.4-40 25
>40 30

Cardiovascular Dysfunction

Tachycardia Score
90-110 5
110-120 10
120-130 15
130-140 20
>140 25
Congestive heart failure absent 0
Mild CHF (pedal oedema) 5
Moderate CHF (bibasal creps) 10
Severe CHF (pulmonary oedema) 15
Atrial fibrillation 10

Central Nervous System Effects

Absent 0
Mild (agitation) 10
Moderate (delirium, psychosis) 20
Severe (seizure, coma) 30

Gastrointestinal effects

Absent 0
Moderate (vomiting, diarrhoea and abdominal pain) 10
Severe (unexplained jaundice) 20

Precipitant history

Negative 0
Positive 10

Likelihood of thyroid storm

>45 Highly suggestive
25-44 Impending storm
<25 Unlikely