I. Definitions of fever and measurement of temperature

  1. Fever = core temp 100.5' F or higher; threshold modified by clinical picture
  2. Night temp normally about 1.5' F higher than morning temp.
  3. Patients with Chronic Renal Failure tend to have lower baseline temperatures
  4. Tympanic thermometers registered an average of .27 degrees Celsius (0.5 degrees Farenheit) lower than rectal thermometers in one study (Arch. Dis. Child. 8/24/2010, e-publication ahead of print at: http://adc.bmj.com/content/early/2010/08/24/adc.2010.185801-JW)

II. Mechanisms of fever

  1. IL-2 release stimulated by neoplasia, autoimmune disease, allergy, & infections
  2. Stimulates release of cytokines (PGs), monokines (IL-1, TNF) which produce fever
  3. Exogenous pyrogens: endotoxin, pepdidoglycan, Ag-Ab complexes stimulate monokine release
  4. Response of pt. to antipyretics gives no indication of the cause of the fever!

III. Use of antipyretics:

  1. In children, ibuprofen was more effective for fever (though no more effective for pain) compared with acetaminophen, according to a meta-analysis of 17 randomized trials in children < 18yo (Arch. Pediat. Adol. Med. 158:521, 2004--JW)
  2. Specific indications:
  1. T > 106' F is deleterious in itself
  2. Pts with ischemic heart dis/bad mitral sten. (fever increases CO & can precipitate failure)
  3. T >101' F in kid<2yo (to avoid febrile sz)
  4. Elderly may get delirious when febrile
  1. Giving antipyretics "PRN" for fever can cause sharp rises & falls in temp which is highly uncomfortable for pt; regularly administered antipyretics may result in greater comfort

IV. "Fever w/u" in hosp'd pt:

  1. Hx, inc. medications (remember drug fever!)
  2. Px--source of infection
  3. Labs: CBC with diff (band count more important than total WBC); Blood cx x 2; clean catch U/A & C/S
  4. Microscopic urine: gm stain of unspun for bact; spun sediment for WBCs
  5. CXR (can always have asymptomatic pneumonia)
  6. By clinical indication, sputum gm stain/cx (within 20min of expectoration); LP; paracentesis; etc.
  7. Histologic examination of bone marrow biopsy may be useful in patients with fever or unknown origin (in particular, may identify hematologic malignancy) (Arch. Int. Med. 169:2018, 2009-JW)

V. Causes of FUO (3wk with T>101'F & neg. fever w/u including cultures, CXR, abdominal imaging e.g. u/s):

  1. Infection 35-40% (TB, endocarditis, closed-space infection; Epstein-Barr virus; Cytomegalovirus; sinusitis; dental infection; Q Fever; HIV & opportunistic)
  2. Malignancy 25-35% (can be secondary to infection of a blocked hollow organ)
  3. Collagen vasc. dis. 15% (esp. polymyalgia rheumatica, giant-cell arteritis)
  4. Thrombotic Thrombocytopenic Purpura
  5. Misc 5-10% (drug fever, esp. sulfonamides; pulm. infarct; MI; IBD; factitious)
  6. Kawasaki Disease
  7. Hemophagocytic syndrome (clinical features include fever, lymphadenopathy, hepatosplenomegaly, cytopenias, and hyperferritinemia; associated with malignancy, infection, and autoimmune disease including HIV)
  8. PET scanning or Gallium scanning can be helpful for dx (see Clin. Inf. Dis. 32:191, 2001--JW)