Wednesday, January 18, 2012

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Hemodialysis - when to start? / Calculation of normalized eGFR

Hemodialysis should be started when:
1) eGFR is < 6 mL/min/1.73 m2
2) eGFR is < 15 mL/min/1.73 m2  and patient is showing signs and symptoms of uremia, unable to control his hydration and blood pressure. 

Cockcroft-Gault formula is a very commonly used formula to get an estimate of the GFR. The unit for eGFR is  mL/min. The classification for stages of chronic kidney diseases on the other hand is based on normalized eGFR i.e. the eGFR per 1.73 m2 and the unit being mL/min/1.73 m2.

Thus we also need to calculate the surface area of the patient's body. It is given by the formula as follows : 

Body Surface Area (m2) = ( [Height(cm) x Weight(kg) ]/ 3600 )½

And the normalized eGFR (mL/min/1.73 m2) = (eGFR/BSA) x 1.73

A clinical example is given below. 
A 45 year old man weighing 70 kg and 180 cm tall has been admitted to the hospital because of fluid overload. He has been treated for the past hours with diuretics but has not been improving. Blood results showed that the serum creatinine level was 550 μmol/LShould the patient be dialysed?

a) the eGFR acc to Cockcroft formula = 14.87 mL/min.
b) the BSA of the patient = 1.87 m2

Thus the normalized eGFR = 13.76 mL/min/1.73 mwhich is indeed an indication for dialysis.


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