Short stature and poor linear growth — formative SAQs

SAQ 1 (10)

A 6-year-old boy is referred because he is the smallest in his class. His height is at the 3rd centile and has tracked parallel to that centile over 18 months. Both parents are short. Examination is normal, with a normal upper-to-lower segment ratio. Bone age matches chronological age. ^[2]

1. Define short stature and state why growth velocity matters more than a single measurement. (3) ^{[2] [5]}
2. List four features that support a normal variant (familial short stature) rather than pathological short stature. (4) ^[2]
3. Outline how you would calculate the mid-parental (target) height and interpret the result. (3) ^[6]

Model answer

Definition and velocity. Short stature is height more than two standard deviations below the mean for age and sex (about the 3rd centile). Growth velocity — the rate of change over serial measurements — matters more than a single point because a child tracking a low parallel channel is usually a healthy variant, whereas downward centile crossing is pathology until proven otherwise. ^{[2] [5]}

Familial short stature features. Short parents with a mid-parental height consistent with the current channel; normal height velocity tracking parallel to the centiles; normal examination including a normal upper-to-lower segment ratio and normal puberty; and a bone age that matches chronological age. Together these support a normal variant rather than disease. ^[2]

Mid-parental height. Using the Tanner approach, the target for a boy is the average of the parental heights plus 6.5 cm, and for a girl the average minus 6.5 cm, with a corridor of about ±10 cm. The child is expected to track within this corridor; a height far below it warrants investigation even if the centile looks normal. The formula is imprecise at the extremes, so use it as a corridor rather than a prediction. ^[6]