Initial von Willebrand factor antigen values in adolescent females predict future values.

introductionDiagnosing von Willebrand Disease (VWD) in adolescent females is challenging as menstruation and physiologic stress elevate von Willebrand factor (VWF) laboratory values.

aimTo develop a VWF prediction model for adolescent females based on initial VWF results.

methodsWe identified female patients aged 9 to 21 years with any VWF laboratory test over a 5-year period (2017-2021) at any Texas Children's Hospital facility. Patient demographics, VWF testing, haemoglobin concentration, serum ferritin and site of clinical testing were collected (initial and subsequent laboratory evaluations). A Bayesian linear regression model was developed. Prediction intervals were analysed to identify thresholds for patients in whom repeat testing was unlikely to identify low VWF levels (< 50%), consistent with VWD.

resultsA total of 6125 adolescent females underwent VWF testing; 1204 (19.7%) had repeat testing. Based on the prediction model, initial VWF antigen values of 80%, 90% and ≥100% carried a 92.6%, 96.6% and ≥98.0% probability of having repeat normal repeat VWF values, respectively. Subjects assessed in outpatient adolescent medicine or gynaecology clinics were more likely to have low VWF values compared to those assessed in the acute care setting (p < .001). Median presenting haemoglobin and serum ferritin were 12.4 g/dL and 13 ng/mL, respectively and were similar in those with normal versus low VWF antigen values.

conclusionRepeat testing in adolescent females whose initial VWF antigen values are ≥90% is unlikely to identify additional patients with VWD. Iron deficiency screening should be performed in all adolescent females.