Marlene has been concerned that Margaretha, at 43 pounds and 48 inches (4 feet) tall, might be too thin. That's a worry for many parents of HIV positive children who fear that their kids may be experiencing the "failure to thrive" -- growth failure -- that's all too common in these youngsters. But in order to know whether there's a real problem, it must be diagnosed properly.

After the age of two, the most reliable measure of a child's overall nutritional status is height. But because there are wide variations in both height and weight in the population, growth failure can't usually be diagnosed with a single measurement. Except in extreme cases, if I find your height at a given moment is below average for your age, all I can say is "You're short." And that might have nothing to do with growth failure. Maybe your parents are short and that's just your genetic heritage. What doctors are interested in is the growth rate, or "growth velocity" -- whether the child is continuing to grow at an appropriate rate over time. The simplest way to determine that is to measure height at least twice each year and, using tables to determine the child's percentile for that age (what percentage of kids are that height or shorter), track changes over time.

If the initial height measurement shows that a child is in, say, the 50th percentile, I'd want to see him or her stay close to that percentile. A low percentile would be fine -- as long as he or she continues to grow well enough to stay in at least that percentile. But if the child dropped from a higher to a lower one, that could mean that he or she may be experiencing growth failure. In Margaretha's case, two years ago she was in the 15th percentile for height. Now she's in the 50th, making her rate of growth above average. She's actually playing catch-up.

Credit for the improvement should go to her good viral control with ddI (Videx), d4T (Zerit) and nelfinavir (Viracept), combined with her mother's constant efforts to boost her food intake. Both factors are very important. In fact, the first step to help kids grow better is to suppress their virus, which often leads to improved appetite. So effective HAART is a must. The other key strategy is getting the most bang for the buck with food. Eliminate empty-calorie items, especially such stomach fillers as sodas, and load kids up with nutrient-rich foods. Always exploit whatever food they're eating. No cracker should go uncovered by peanut butter. Chips shouldn't be eaten without the bean dip. Make every bite count.

Despite Marlene's concern about her daughter's low weight, Margaretha has actually gone from the 5th percentile to the 25th in the past two years. Because of the wide variability in childhood weight levels, measuring weight may be of limited value in identifying growth failure (unless the underweight is severe). As with Margaretha, low weight may just mean that the child is a picky eater who's naturally thin. It's not a problem as long as he or she is still gaining height appropriately. That's what Margaretha is now doing, having moved from the low end up to almost average height. I think she's just where she needs to be. And, yes, she's skinny, but in the normal range -- and probably looks just like her mom looked at this age.