Urea
Increase in plasma urea
Non renal
Urea is elevated in the absence of intrinsic renal disease

Mild dehydration - common
High protein diet
Gastrointestinal haemorrhage - a protein meal of blood in the gut!
Renal
Urea is elevated due to intrinsic renal disease or restriction in urine flow
Interpretation of urea result takes place in conjunction with creatinine results as part of U+E (urea and electrolytes)
Decrease in plasma urea
Low protein intake
Liver disease
Haemodilution - pregnancy
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Serum urea = 2.5 - 7.8 mmol/L