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Renal Calculations |
Creatinine Clearance - measured
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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) Males (kg) = 50 kg plus 0.9 kg for every cm of height > 152 cm Females (kg) = 45.5 kg plus 0.9 kg for every cm of height > 152 cm Reference Interval: 90 - 150 mL/min (lower values expected in older subjects). Notes: GFR Estimate by MDRD Formula eGFR (mL/min/1.73m2)= 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:
On-line calculator for eGFR by MDRD GFR Estimate by CKD-EPI Formula eGFR (mL/min/1.73m2): Females: The CKD-EPI 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 m2 Body Surface Area (BSA) BSA(m2) = 0.007184 x Ht(cm)0.725 x wt(kg)0.425 (Dubois and Dubois formula, 1916)CrCl(mL/min/1.73m2) = U CRCL(mL/min) x 1.73/BSA(m2) |
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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 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 0.012} Notes:
Ionised calcium corrected for in-vitro 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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