BSA (Haycock)

About BSA (Haycock)

The Haycock formula, published by G. B. Haycock, G. J. Schwartz, and D. H. Wisotsky in 1978 in the Journal of Pediatrics, is a body surface area equation derived specifically to be valid across the entire lifespan, from neonates to adults. The authors measured body surface area in 81 subjects ranging from infants to adults and derived their formula by regression, finding that a single equation with appropriately chosen exponents fit the data well across the full age and size range. This makes Haycock the preferred BSA formula in pediatric and neonatal practice, where the adult-derived Du Bois formula is less well validated.

How the formula works

The Haycock formula is BSA (m^2) = 0.024265 x weight(kg)^0.5378 x height(cm)^0.3964. The exponents differ from those in the Du Bois formula (0.425 and 0.725): Haycock's weight exponent is higher (0.5378) and height exponent lower (0.3964), reflecting the different body proportions of infants and children, in whom weight scales more strongly with surface area than height does. The constant 0.024265 calibrates the result to square meters. For a 175 cm, 75 kg adult, Haycock gives BSA = 0.024265 x 75^0.5378 x 175^0.3964 = approximately 1.91 m^2, in close agreement with Du Bois and Mosteller.

Evidence and pediatric validation

Haycock's original validation in 81 subjects from neonates to adults reported a better fit across the full size range than the Du Bois formula, which had been derived only from adults. Subsequent pediatric pharmacology references have adopted Haycock as the preferred BSA formula for infants and children, and it is used in pediatric drug dosing, renal function estimation, and cardiac output indexing. In adults, Haycock agrees with Du Bois and Mosteller to within about 2 percent, so the choice among them rarely matters clinically for typical adults but can matter in small infants where the adult-derived formulas are less accurate.

Clinical use

Haycock's formula is used in pediatric and neonatal medicine for drug dosing (particularly chemotherapy and antibiotics in infants), for cardiac output indexing in pediatric cardiology, and for renal function estimation in pediatric nephrology. It is the formula recommended by many pediatric references and is built into pediatric drug-dosing calculators and electronic medical records that support pediatric care.

Interpretation

Average adult BSA is about 1.7 to 1.9 m^2; in a term neonate it is about 0.2 to 0.25 m^2. The Haycock formula gives values essentially identical to Du Bois and Mosteller for typical adults and more accurate values for infants and small children, making it a good all-purpose BSA formula across the lifespan.

Limitations

Like all BSA formulas, Haycock's equation assumes average body proportions and does not account for the variability in drug clearance that body composition, age, and organ function produce. In obese adults, BSA is overestimated because the allometric exponents assume average proportions. The formula is most valuable in pediatric and neonatal settings, where its derivation across the size range gives it an advantage over adult-derived formulas. For most adult applications, Mosteller or Du Bois is standard, but Haycock is a reasonable alternative that gives nearly identical results.