Ch04-9781975113285

Useful Formulae   1 1

ANION GAP (URINE)

) − U

UAG = (U

 + U

[Na + ]

[K + ]

[Cl − ]

( all in mmol/L )

• Normal = slightly positive • UAG is negative in diarrhea-induced nongap metabolic acidosis ( enhanced urinary NH 4 + excretion). • UAG is positive in distal RTA-induced nongap metabolic acidosis ( impaired urinary NH 4 + excretion). • See Chapter 15, Acid-Base Disorders, for differential diagnosis. BODY MASS INDEX

BMI = wt/(ht) 2 ( wt in kg, ht in m )

• <18.5 = underweight • 18.5-24.9 = normal weight • 25-29.9 = overweight • >30 = obese • >40 = morbidly obese CREATININE CLEARANCE/GLOMERULAR FILTRATION RATE

Estimated (Cockcroft-Gault Formula) CrCl = [(140  −  age) × weight]/[serum Cr × 72] × 0.85 ( if female ) ( weight in kg, Cr in mg/dL) Estimated (MDRD) eGFR = 175 × (SCr) − 1.54  × age −0.203 × 0.742 ( if female ) × 1.21 ( if black ) ( eGFR in mL/min per 1.73m 2 , Cr in mg/dL )

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