Urea and electrolytes

Nota:

• usually w/in 2 hrs,  30 mins if urgent

1. Na+

   Nota:

   • extracellular cation
   1. Hyponatremia (Na <120 mmol/L)

      Nota:

      • due to either loss of sodium or overload of water or both.  The following list contains the relatively common and important causes of hyponatraemia.  For more complex cases, it is necessary to have simultaneous samples of both blood and urine for estimation of osmolality and electrolytes.
      1. + edema
         1. CCF
         2. Liver failure
         3. nephrotic syndrome
      2. +dehydration
         1. diarrhea
         2. Addison's disease
         3. Renal salt wasting
      3. +normal volume
         1. D + V follwed by drinking excess water
         2. diuretics

            Nota:

            • Monitoring: Prior to the initiation of therapy and after 2/52, 3/12, 6/12 and then 6-12/12  or more frequently in the elderly or in patients with renal disease, disorders affecting electrolyte status or those patients taking other drugs eg corticosteroids, digoxin.
            1. may occur w/in 1-2 weeks of initiation of therapy but may develop after many years of therapy
         3. ACE inhibitors
      4. + innapprop ADH secretion
         1. drug therapy
         2. chest disease
         3. CNS disease
      5. complications varied

         Nota:

         • from seizures and coma in younger ppl,  wherby chronic diuretic therapy can bring down hugely in old ppl w/little effect
2. K+

   Nota:

   • intracellular cation
   1. hyperkalemia (K >5.5 mmol/L)
      1. hemolysis and delayed separation over-night storage in a 'fridge'
      2. renal failure
      3. potassium retaining diuretics (eg spironolactone)
      4. ACE inhibitors
   2. hypokalemia (K < 3.5 mmol/L)
      1. diuretics
      2. D + V
      3. ileostomy
      4. chronic purgative abuse
      5. excessive liquorice
      6. elderly pts w/poor nutrition (catabolic state)
3. Urea

   Nota:

   • waste product formed from 2 ammonia + 1 CO2, allows excretion of excess nitrogen from body
   1. Low
      1. pregnancy
      2. starvation
      3. chronic liver disease
   2. High
      1. renal failure
         1. high urea with a normal creatinine often points to dehydration or CKD.
      2. dehydration
      3. transiently after eating high protein meal
      4. following a significant gI bleed
4. Creatinine

   Nota:

   • waste product formed from creatine in muscles, renally excreted serves as measure of renal function
   1. high
      1. dehydration
      2. dietary intake
      3. renal failure
      4. body building
   2. low
      1. low or falling muscle mass
         1. eg very old, malnourished
5. bicarbonate

   Nota:

   • important anion (-) in acid base balance balances H+
   1. low
      1. metabolic acidosis
         1. renal failure
         2. GI fluid losses
   2. high
      1. respiratory acidosis
         1. CO2 retention in COPD