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Useful Formulae
1 1
ANION GAP (URINE)
UAG = (U
[Na
+
]
+ U
[K
+
]
)
−
U
[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
)