Pathology updates 

26/10/2017 00:00 

Health Services Laboratories, which processes samples sent to UCLH, is moving its mycology service for dermatophytes from a culture method to a polymerase chain reaction (PCR) method.

The detection of dermatophyte fungal pathogens has now evolved to using high sensitivity PCR testing, replacing the conventional agar plate culture.

This change will reduce the overall turnaround time by two weeks: from the previous three weeks for culture to 72 hours for the diagnosis of dermatophyte infection, and to seven days for the final reporting of yeast or other mould infections from skin specimens.

It will also increase the detection of fungal infection compared with microscopy and culture combined (36.4 percent from 33.6 percent).

Furthermore, the targeting of the specific pathogens associated with superficial fungal infection will prevent the over-reporting of insignificant fungi that are contaminants.
The PCR for dermatophytes detects the following species:

  • Trichophyton mentagrophytes complex
  • Trichophyton tonsurans / equinum
  • Trichophyton violaceum
  • Trichophyton rubrum complex
  • Microsporum audouinii / canis / ferrugineum

Hair and nail specimens where microscopy and culture has been requested will automatically be tested by PCR. Skin specimens, in addition to PCR, will have microscopy and seven-day culture for yeast and moulds. 

Contact: Dr Bruce Macrae, clinical lead, bruce.macrae@nhs.net or Rebecca Gorton, HSL senior clinical scientist, rebecca.gorton@hslpathology.com

25-OHD measurement change

The method for 25-hydroxyvitamin D (25-OHD) measurement has changed from liquid chromatography-tandem mass spectrometry (LC-MS/MS) to immunoassay.

While the LC-MS/MS assay provided a breakdown of results (25-OHD2, 25-OHD3, total 25-OHD) the immunoassay provides the total 25-OHD only, which is the value used to assign vitamin D status. There are no changes to interpretative ranges.

The immunoassay compares well with LC-MS/MS results in the great majority of cases. The exception will be in a minority of patients receiving vitamin D2 supplementation where results may be lower than expected. The manufacturer states 92 percent detection of 25-hydroxyvitamin D2.

Contact: Francis Lam, consultant biochemist, francis.lam@nhs.net, 020 3908 1365 or the duty biochemist, dutybiochemist@uclh.nhs.uk, 020 3447 9405.

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