Cutoff point, upper and lower QUS parameters values in diagnosing demineralisation in cases with ESRD

Dana Bucuras; Dan Poenaru; Ovidiu Golea

Background: The British Society for Osteoporosis proposed a method for comparing different diagnostic measurements for BMD. It defines the upper and the lower limit for the investigated assay, that will identify osteoporosis with a sensitivity of 90% (the upper limit) and a specificity of 90% (the lower limit), compared with the defined golden standard method, mainly DXA for spine or hip. This rationale generate small number of false positive or negative results.

Materials and methods: One hundred and thirty-one cases with ESRD were evaluated by means of DXA and QUS with ISCD validated devices: Hologic Sahara/Hologic Hologic, aparat Delphi W (S/N 70489), lumbar L₁–L₄, anteroposterior technique, nondominant hip.

Table 1 Upper limit, lower limit and threshold value for QUI compared with DXA results
	Upper limit (90% sensitivity)	Lower limit (90% specificity)	Threshold values
T score < −1 femural neck	93.90	65.50	74.40
T score < −2.5 femoral neck	76.90	61.40	69.60
T score < −1 total hip	93.90	67.20	76.10
T score < −1 total hip	76.50	59.20	69.60
T score < −1 spine	94.50	69.70	80.90
T score < −1 spine	85.70	62.20	67.50

Results: We defined bone demineralisation in cases of T score below −1, confirmed by increased markers of bone turnover. We identified than the limits for each QUS parameter in diagnosis bine demineralisation. We also performed ROC diagnostic curves, comparing QUS parameters with DXA results, and we identified the best threshold value for QUI.

The best parameter seemed to be QUI. We selected different values for each measured sites. Table 1.

The threshold values were identified by finding the best specificity and sensitivity from the series of number. This values are listed in Table 2.

Table 2 Diagnostic quality and power for each identified QUI threshold value
Threshold values	Sensitivity	Specificity	PPV	NPV
74.40	60.25	77.5	77.38	77.71
69.60	76.19	66.48	25.39	92.42
76.10	64.77	73.17	83.33	47.61
69.60	80.0	66.9	30.7	94.8
80.90	59.15	70.4	65.6	67.7
67.50	70.23	62.5	67.7	86.4

The most precise interval is that one compared with the femoral neck compartment. When a patient has QUS result between the to limits, there is a very good sensitivity and specificity in diagnosing bone demineraşlisatoin. QUS can be used as a screening tool, for decreasing the unnecessary DXA measurements, also in these patients. The 90–90 approach seems to be better then the threshold value method, because of the higher NPV and PPV.

Conclusion: QUS can be used as a screening method to identify the target population with decreased bone mass, also in patients with ESRD.

Endocrine Abstracts

P79