Fever classification

Pyrexia (fever) can be classed as:

• Low grade: 38–39°C (100.4–102.2°F)
• Moderate: 39–40°C (102.2–104.0°F)
• High-grade: 40–42°C (104.0–107.6°F)
• Hyperpyrexia: Over 42°C (107.6°F)

Febricula is a mild fever of short duration, of indefinite origin, and without any distinctive pathology.^[1]

• Sustained fever: the fluctuation in temperature during a 24-hour period is 0.3 °C (0.5 °F) or less.
• Remittent fever: the temperature is elevated, and it falls each day, but not to normal, remaining 37.3 °C (99.2 °F) or above. The excursion in temperature is more than 0.3 °C (0.5 °F) and less than 1.4 °C (2.5 °F).
• Intermittent fever: the temperature is elevated but falls to normal (37.2 °C [99 °F] or below) each day. The excursion in temperature is more than 0.3 °C (0.5 °F) and less than 1.4 °C (2.5 °F).
• Hectic fever: remittent or intermittent fever, with a difference of 1.4 °C (2.5 °F) or more between peak and trough.^[2]

The periodicity of fever generally offers little diagnostic value in ascertaining the etiology of fever. Characteristic fever patterns include:^[3]

• Sustained fever (suggestive of brucellosis, drug fever, lobar pneumonia, tularemia, typhoid, typhus)
• Remittent fever (suggestive of tuberculosis, mycoplasma pneumonia, malaria, legionellosis)
• Intermittent fever (suggestive of malaria, kala-azar, pyaemia)

• Double quotidian fever (suggestive of Still’s disease, legionellosis, miliary tuberculosis, kala-azar)
• Quotidian fever (suggestive of Plasmodium falciparum or Plasmodium knowlesi malaria)
• Tertian fever (suggestive of Plasmodium vivax or Plasmodium ovale malaria)
• Quartan fever (suggestive of Plasmodium malariae malaria)
• Alternate-day fever (suggestive of response to antipyretic dosage schedule)

• Hyperpyrexia (suggestive of intracranial hemorrhage, septicemia, Kawasaki disease, thyroid storm, drug fever)
• Hectic or spiking pattern (suggestive of biliary or urinary tract infection, endocarditis)
• Morning temperature spikes (s/o typhoid fever, tuberculosis, polyarteritis nodosa)
• Relapsing pattern (suggestive of Borrelia recurrentis, typhoid fever, malaria, brucellosis, rat-bite fever)
• Irregular pattern (suggestive of factitious fever)
• Pel-Ebstein pattern (suggestive of Hodgkin’s lymphoma)
• Picket fence pattern (suggestive of acute mastoiditis complicated by transverse sinus thrombosis)
• Saddleback pattern (suggestive of dengue fever, leptospirosis, poliomyelitis, human granulocytic ehrlichiosis)
• Wunderlich curve pattern (suggestive of typhoid fever)