Accuracy of diagnostic testing in primary ciliary dyskinesia

Abstract

Diagnosis of primary ciliary dyskinesia (PCD) lacks a "gold standard" test and is therefore based on combinations of tests including nasal nitric oxide (nNO), high-speed video microscopy analysis (HSVMA), genotyping and transmission electron microscopy (TEM). There are few published data on the accuracy of this approach.Using prospectively collected data from 654 consecutive patients referred for PCD diagnostics we calculated sensitivity and specificity for individual and combination testing strategies. Not all patients underwent all tests.HSVMA had excellent sensitivity and specificity (100% and 93%, respectively). TEM was 100% specific, but 21% of PCD patients had normal ultrastructure. nNO (30 nL·min −1 cut-off) had good sensitivity and specificity (91% and 96%, respectively). Simultaneous testing using HSVMA and TEM was 100% sensitive and 92% specific.In conclusion, combination testing was found to be a highly accurate approach for diagnosing PCD. HSVMA alone has excellent accuracy, but requires significant expertise, and repeated sampling or cell culture is often needed. TEM alone is specific but misses 21% of cases. nNO (⩽30 nL·min ) contributes well to the diagnostic process. In isolation nNO screening at this cut-off would miss ∼10% of cases, but in combination with HSVMA could reduce unnecessary further testing. Standardisation of testing between centres is a future priority. @ERSpublications Combination testing in PCD diagnosis remains the most accurate approach, but standardisation is needed

Clinical care for primary ciliary dyskinesia: current challenges and future directions

“…TEM was once the "gold standard" for PCD diagnosis. However, it is now known that 15-20% of PCD cases have disease-causative mutations but normal ultrastructure by TEM [30,39,[41][42][43]. A quantitative approach to cilia evaluation is recommended, but there is no agreement on the minimal number of cilia scored or on the terminology used for ultrastructural defects.…”

“…immotile or circular cilia) are relatively easy to detect, subtle changes are difficult to differentiate from secondary defects by HSVMA and are only likely to be picked up by specialised scientists in high-throughput centres and even then risk being missed. There are significant challenges in standardising HSVMA testing and in using appropriate terminology for different beat patterns [41], so it is important to address these in order to generate comparable data.…”

Diagnostic testing in primary ciliary dyskinesia

“…As discussed in our manuscript [1] and the accompanying editorial by Haarman and Schmidts [5], generalisability of our findings should be considered with caution. Accurate analysis of ciliary function by HSVMA and of ultrastructure by TEM depends on expertise.…”

“…[1] This was clearly described in the methods section; and several sensitivity analyses tested the robustness of our results by varying different parameters. Most notably, we began the discussion section [1] by describing the lack of a single 'gold reference standard' (second paragraph) as the major limitation of our study. We highlighted that we used a surrogate reference standard, which was an expert multidisciplinary consensus, based on results from all available diagnostic tests.…”

“…For example, we could have used TEM alone as a single reference standard, and calculated the accuracy of the other tests compared to TEM, taking into consideration that the latter has excellent specificity but limited sensitivity (70-90%). For completeness, we did this for TEM and for HSVMA (online supplementary table S2 [1]), but given that this was not our primary approach and that pre-existing data about the degree of imperfection were highly variable, we decided not to make any adjustments.…”