Biochemistry Calculations 

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Renal Calculations 
Creatinine Clearance  measured


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Renal Calculations

Creatinine Clearance  measured Measured using creatinine determined plasma and 24 hour urine collection. Creatinine Clearance (mL/min) = (U Creat x Vol x 16.7) / (Pl Creat x time) Urine creatinine concentrations in mmol/L Reference Interval: 90  150 mL/min (lower values expected in older subjects). Notes:
Calculated Creatinine Clearance (Cockcroft and Gault) Creatinine Clearance (mL/min) = {(140  Age) x Wt x F}/ (P Creat x 0.814) F= 1 (males); F=0.85 (females) Reference Interval: 90  150 mL/min (lower values expected in older subjects) Notes: (estimated from plasma creatinine, age, height and sex) Creatinine Clearance (mL/s) = {(140  Age) x Wt x F}/ {P Creat x 0.814} F= 1 (males); F=0.85 (females) Estimated Lean Body Mass from patient's height: Reference Interval: 90  150 mL/min (lower values expected in older subjects). Notes: GFR Estimate by MDRD Formula eGFR (mL/min/1.73m^{2})= 175 x [SerumCreatinine(umol/L) x 0.0113]^{1.154} x Age(years)^{0.203} (x 0.742 if female) This version of theMDRD formula is for serum creatinine assays aligned with IDMS (the international reference method). An IDMS aligned assay is in use at SydPath. Notes:
Online calculator for eGFR by MDRD GFR Estimate by CKDEPI Formula eGFR (mL/min/1.73m^{2}): Females: The CKDEPI formula is only valid for serum creatinine assays aligned with IDMS (the international reference method). An IDMS aligned assay is in use at SydPath. Notes:
Fractional Excretion Of Sodium (FENA) Fractional Excretion Of Sodium (FENA) FENA(%) = {U Na / Pl Na x 100} / {U Cr * 1000 / Pl Cr} All concentrations in mmol/L except plasma creatinine in umol/L. Interpretation:
Creatinine Clearance per m^{2} Body Surface Area (BSA) BSA(m^{2}) = 0.007184 x Ht(cm)^{0.725} x wt(kg)^{0.425 }(Dubois and Dubois formula, 1916) CrCl(mL/min/1.73m^{2}) = U CRCL(mL/min) x 1.73/BSA(m^{2}) 

General Calculations 
LDLC (mmol/L) = Total Cholesterol  HDLCholesterol  (Triglycerides / 2.2) All values in mmol/L Notes: %SAT = 3.982 x Iron (umol/L) / Transferrin (g/L) Note: Indirect Bilirubin (umol/L) = Total Bilirubin (umol/L)  Direct Bilirubin (umol/L) Indirect bilirubin is a measure of unconjugated
bilirubin Used to correct plasma total calcium measurements for effects of changes in albumin concentration. Corrected calcium can then be compared with usual reference intervals. Calcium (corrected, mmol/L) = Calcium (measured, mmol/L) + {(40  albumin (g/L)) x 0.02} Notes:
Ionised calcium corrected for invitro pH changes
Sodium corrected for Hyperglycaemia Used in patients with very high serum glucose concentration (eg > 30 mmol/L) to estimate serum sodium after reduction of glucose with insulin. Sodium (corrected) = Sodium (measured) + glucose / 4 (all values in mmol/L). Note: Variability in result due to measurement uncertainty approximately +/ 5 mmol/L. A calculation to assist with determining the cause of a metabolic acidosis of unknown origin. Anion Gap = Sodium + Potassium  (bicarbonate + chloride) (all measurements in mmol/L) Reference interval: 10  18 mmol/L Note: variability in result due to uncertainty in measurements approx. +/ 5 mmol/L. For more information and interpretation see page: Chloride and the Anion Gap A calculation to assist with identifying the presence of unmeasured substances in the serum (eg ethanol, methanol, mannitol) Osmolar Gap = measured osmolality  calculated osmolality Calculated osmolality = 2 x sodium + urea + glucose (all measurements in mmol/L) If an ethanol result is available, osmolality can be calculated as follows: Calculated osmolality = 2 x sodium + urea + glucose + 270 x ethanol (in %*) Calculated osmolality = 2 x sodium + urea + glucose + 1.25 x ethanol (in mmol/L) Reference interval: 0  10 mmol/L Note: variability in result due to uncertainty in measurements approx. +/ 7 mmol/L. * units used at SydPath and to express the legal driving limit, eg 0.05% (=11 mmol/L) For further information see SydPath page: Osmolality 

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