Nephrology‎ > ‎

Elevated BUN / Hematuria / Polyuria / Urinary Casts

  • ELEVATED BUN: Volume Contraction; Bleeding; Renal Failure, Corticosteroid


    Microscopic Hematuria
    • First: Differentiate Polyuria from Urinary Frequency
    • DDx of Polyuria
      • Common (>1/10)
        • Diuretics
        • Caffeine
        • Alcohol
        • DM (Osmotic Polyuria)
        • Li (Nephrogenc DI)
        • HF
      • Infrequent (1/100)
        • Hypercalcemia (Mechanism: .....)
        • Hyperthyroidism (Mechanism: Elicit symptoms of thyrotoxicosis (sweating, heat intolerance), as this stimulates thirst and causes an increase in circulating natriuretic peptides, resulting in greater excretion of both sodium and water and hence leading to symptoms of polyuria: Ref: BMJ 2013 as below)
      • Rare (1/1000)
        • Chronic Renal Failure (Due to inability to retain water due to its inability to concentrate urine due to its inability to create a medullary concentration gradient)
        • Primary Polydipsia (Difficult to treat; Due to low Na, may need hospital admission for treatment)
        • Hypokalemia (Due to central DI)
      • Very Rare (1/ 10,000)
        • DI
          • Central (infiltration of or damage to the pituitary as a result of a tumour, a head injury, neurosurgery, haemochromatosis, or sarcoidosis Ref: BMJ 2013 as below)
          • Nephrogenic
    • Work up
      • Summary of investigations

        Primary care

        Home fluid balance chart
        Urine dipstick
        Capillary blood glucose
        Serum urea and electrolytes, calcium
        Random/fasting glucose or glycated haemoglobin (HbA
        1c) Urine and plasma osmolality

        Urine electrolytes

        Secondary care (endocrinology)

        Water deprivation test*
        Desmopressin administration
        Measurement of plasma antidiuretic hormone Anterior pituitary hormones†
        Magnetic resonance scan of brain/pituitary

        *Urine and plasma osmolalities are measured in response to fluid deprivation and subsequent administration of desmopressin (antidiuretic hormone)

        †Thyroid stimulating hormone, prolactin, luteinising hormone, follicle stimulating hormone, growth hormone, adrenocorticotrophic hormone 

  • 1. Investigating polyuria BMJ 2013


    1. Approach to the patient with red or brown urine Up-to-date