Blood Urea Nitrogen (BUN)
RenalNormal range
10–20 mg/dL
SI: 3.6–7.1 mmol/L
Critical high: > 100 mg/dL
☎ When to call
Escalate the trend with creatinine and urine output — BUN alone rarely drives the call.
What you do
- BUN:Cr ratio > 20:1 suggests prerenal (dehydration) — look at intake and volume status
- Rising BUN + rising Cr = the kidney itself; review nephrotoxic meds (NSAIDs, contrast, vanco)
Causes of HIGH blood urea nitrogen
Causes of LOW blood urea nitrogen
Source: Pagana, Mosby's Manual of Diagnostic and Laboratory Tests, 7th ed.Reference only — verify against your facility's policy.
