(The New York Times News Service) -- Like most pediatricians, Dr. Eric Poon usually obtains a child's weight and height during an examination and records them on a set of standardized growth charts.

This allows him to compare the child's growth with that of thousands of other children and to determine whether it is adequate, inadequate or, in these times of rampant obesity, too adequate.

Poon follows hundreds of patients in his New York City clinic, in the heart of Chinatown, but one child he was particularly concerned about was Kevin Ngai, 4.

Although Kevin's height was progressing along the 25th percentile, he had been markedly underweight since birth. Every point on his weight growth curve scrapes the 5th percentile, the border between normal and abnormal. Poon found nothing else in Kevin's physical examination suggesting an underlying serious illness, but just to make sure Kevin was absolutely healthy, Poon ordered a battery of medical tests.

All came back normal and, in fact, Poon's clinical observations were correct. Kevin is a small boy but perfectly healthy; the growth charts, however, were based on data that no longer represent the population of children in the United States.

Pediatricians have long complained about inaccuracies associated with standardized growth charts. Until recently, those most widely used were developed in the 1970s and were based on not much more than 10,000 infants and children living in Ohio between 1929 and 1975.

Because almost all the children studied were white, middle class and formula fed, the charts fail to reflect several differences in growth among different children. For example, healthy breast-fed babies tend to gain weight more slowly than their formula-fed counterparts. Asian children are often smaller than Caucasian children. As a result, a pediatrician may mistakenly conclude that a particular child is not growing or gaining weight adequately when, in fact, he or she is.

Equally problematic, two different groups of children were used for the overlapping charts covering children from birth to 36 months and from 2 years to 18 years.

This means that the same 24- to 36-month-old child can measure in a different percentile when progressing from one chart to the next, often leading to misdiagnoses and expensive clinical tests. Finally, the charts developed to compare weight for stature end at 10 for girls and 11 for boys, making it difficult to follow the growth of teen-agers.

To correct these problems, several nutritionists, pediatricians and statisticians at the National Center for Health Statistics, the National Institutes of Health and the Centers for Disease Control and Prevention have compiled a large sampling of new data from several recent annual national health and nutrition surveys based on millions of children. Their comprehensive data, covering children from birth to 20, better reflect the country's racial and ethnic diversity and include formula and breast-fed babies.

The improvement is striking. In the January issue of Pediatrics, the team reported that the new charts were significantly more accurate for monitoring the growth of infants, children and adolescents.

The most important feature of the new growth charts is the inclusion of a measure called body mass index, which is calculated by dividing the weight by the height squared. BMI is commonly used to determine if adults are overweight and correlates well with a person's total body fat. Nutrition experts have long advocated that BMI be applied to children and teen-agers because a majority of overweight adults start as overweight children.

Dr. Robert Kuczmarski, a nutritionist at the National Institutes of Health and one of the study's authors, noted: "Our data show that by the age of 8 you can predict with great precision which child is likely to be overweight later in life. BMI is one extra tool that will allow physicians to track this trend and, hopefully, do something about it."

Dr. Susan Baker, a pediatrician at the Buffalo Children's Hospital and chairwoman of the American Academy of Pediatrics Nutrition Committee, agrees. "Malnutrition is rarely seen in the United States today and the biggest problem we are seeing related to growth is obesity," Baker said. "Being overweight puts you at direct risk for Type 2 diabetes, hypertension, stroke and heart disease, all leading causes of death in the United States."

Copyright 2002 The New York Times News Service. All rights reserved.