The epidemiology of kidney stones in Belgium based on Daudon’s morpho-constitutional classification: a retrospective, single-center study

Background: Increasing evidence highlights the robust clinical value of morpho-constitutional clas-sification proposed by Daudon.Methods: We retrospectively analyzed the data of 5480 samples submitted for Daudon's classification between 2007 and 2013 to identify the main pro-lithogenic metabolic abnormalities involved in the formation of stones in Belgium.Results: Among 5027 stones submitted by 4975 patients, the distribution of stones steadily increased with age in both genders, reaching a maximum between 40 to 50 years and decreasing thereafter. Men submitted more stones (3549) than women (1426) with global men-to-women ratio at 2.4 (1.0 to 2.79). In the whole series, type Ia was a main morpho-constitutional presentation of whewellite (surface morphology), accounting for 41.9%; the types Ib, Ic, Id and Ie corresponded to 2.2%, 0.16%, 0.94% and 0.46%, respectively. Type IIa accounted for 16.4% and types IIb and IIc for 5.7% and 0.18% of weddellite stones. Types IIIa, IIIb, IIIc and IIId accounted for 4.4%, 3.8%, 0.1% and 0.3%, of uric acid and urate stones respectively. The frequency of calcium phosphate type IVa was 4.7% followed by type IVb (3.5%), IVc (1.3%), IVd (1.4%) and IVa2 (0.3%). Type Va (cystine stones) accounted only for 1.1% and Vb for only 0.1%. The rare, but very specific types Ic, Ie, Id, IIId, IVa2 and V pointed to precise entities such as primary hyperoxaluria type 1, enteric hyperoxaluria, urinary tract abnormalities, hyperuricosuria with diarrhoea, distal tubular acidosis and cystinuria respectively. In terms of the major physico-chimical component, 75.4% of stones contained calcium oxalate (whewellite (52%) and weddellite (22.7%)), 12% calcium phosphate (carbapatite (6.7%)), and 9.8% uric acid, mainly anhydrous (9.1%). The struvite stones accounted for 106 (2.1%) and predominated in women.Conclusions: High frequency of types Ia and IIa suggest that diet related hyperoxaluria and idiopathic hypercalciuria are the leading lithogenic disorders in Belgian kidney stone formers.