PARATHYROID HORMONE –

JUST WHEN YOU THOUGHT YOU UNDERSTOOD IT............?

Alison Almond, Chris Isles, Ken Donaldson, Sue Robertson, Simon

Walker, Andy Ellis, Ewan Bell, Scottish Biochemist Clinical and Research

Network

A COMPARISON OF PTH ASSAYS

• Background to the study• ‘The Troll’s Guide’ to PTH Biochemistry• History of PTH assays• Comparison of PTH assays• Clinical implications• The way forward…..other than to the bar!

METABOLISM OF PTHPTH

NH2

1

COOH

84

ACTIVE END INACTIVE END

1 34NH2 COOH

35 84

LIVER

ELIMINATED IN LIVER RE-ENTERS CIRCULATION.

EXCRETED BY KIDNEYS

HISTORY OF PTH ASSAYS

• 1960’S- Berson described first RIA using single radiolabelled antibody directed at the C-terminal of PTH.

NH2 COOH1 84

YPTH

HISTORY OF PTH ASSAYS

• 1960’S- Berson described first RIA using single radiolabelled antibody directed at the C-terminal of PTH.

• Problems-picked up all C-terminal fragments so PTH measurements correlated poorly with bone histology (Andress DL et al.Journal of Clinical Endocrinology and Metabolism 1986;63:1163-1169)

NH2 COOH1 84

Y

HISTORY OF PTH ASSAYS(2)

• 1980’s-2-site IRMA. C-terminal antibody + solid phase,attached to radio-labelled antibody to N-terminal (epitopes 15-34).2nd generation or so called ‘intact PTH’.Proto-type-Nichols ‘Allegro’.

NH2 COOH1 15 34 84

YPTH

SOLID PHASE ie.plastic bead

YI125

HISTORY OF PTH ASSAYS(2)

• 1980’s-2-site IRMA. C-terminal antibody + solid phase,attached to radio-labelled antibody to N-terminal (epitopes 15-34).2nd generation or so called ‘intact PTH’.Proto-type-Nichols ‘Allegro’.

NH2 COOH1 7 15 34 84

YPTH

SOLID PHASE ie.plastic bead

YI125

Brossard et al.Clinical Chemistry2000; 46:697-703

“..once GFR<30 ml/min/1.73msq reached PTH had decreasedfrom 79% to 68%, and non-(1-84)PTH had increased from 21% to 32%.....in haemodialysed patients ...non-(1-84)PTH accounted for 50% of the iPTH.”

HISTORY OF PTH ASSAYS(3)

• 1992-2-site IRMA. C-terminal antibody + solid phase,attached to radio-labelled antibody to N-terminal , this time to epitopes 1-6 .3rd generation, so called ‘Bio-intact PTH’ or ‘whole PTH’.

NH2 COOH1 6 15 34 84

YPTH

SOLID PHASE ie.plastic bead

YI125

SINGLE PATIENT STUDY - METHOD

SINGLE PATIENT STUDY - METHOD

• 21 haemodialysis patients from DGRI consented to participate.

SINGLE PATIENT STUDY - METHOD

• 21 haemodialysis patients from DGRI consented to participate.

• 5mls of EDTA plasma was taken from each patient before dialysis

SINGLE PATIENT STUDY - METHOD

• 21 haemodialysis patients from DGRI consented to participate.

• 5mls of EDTA plasma was taken from each patient before dialysis

• Specimens were centrifuged, separated and divided into 5 aliquots of 1ml and frozen at DGRI lab.where one sample from each patient was retained.

SINGLE PATIENT STUDY - METHOD

• 21 haemodialysis patients from DGRI consented to participate.

• 5mls of EDTA plasma was taken from each patient before dialysis

• Specimens were centrifuged, separated and divided into 5 alliquots of 1ml and frozen at DGRI lab.where one sample from each patient was retained.

• 4 remaining sets were sent to UK NEQAS , RIE who retained one and distributed other 3 on dry ice to GRI,Borders and Kirkcaldy.

SINGLE PATIENT STUDY - METHOD

• 21 haemodialysis patients from DGRI consented to participate.

• 5mls of EDTA plasma was taken from each patient before dialysis

• Specimens were centrifuged, separated and divided into 5 alliquots of 1ml and frozen at DGRI lab.where one sample from each patient was retained.

• 4 remaining sets were sent to UK NEQAS , RIE who retained one and distributed other 3 on dry ice to GRI,Borders and Kirkcaldy.

• All specimens were analysed on the same day and results returned to UK NEQAS for analysis.

ONE PATIENT – 5 LABORATORIES

183.47

163.57

139.9

126.4

53.8

0 20 40 60 80 100 120 140 160 180 200

PARATHYROID HORMONE LEVEL (pmol/L

DiaSorin Liaison (GRI)

Beckman Access (BORDERS)

Roche Elecsys (DGRI)

Siemens Centaur (KIRKCALDY)

Siemens Immulite (RIE)

ONE PATIENT – 5 LABORATORIES

183.47

163.57

139.9

126.4

53.8

0 20 40 60 80 100 120 140 160 180 200

PARATHYROID HORMONE LEVEL (pmol/L

DiaSorin Liaison (GRI)

Beckman Access (BORDERS)

Roche Elecsys (DGRI)

Siemens Centaur (KIRKCALDY)

Siemens Immulite (RIE)

3.4 FOLD DIFFERENCE

1.4 -4.2 FOLD DIFFERENCE

IN EACH OF THE 17 OTHER PATIENTS.....

HIGHEST AND LOWEST PTH FOR EACH PATIENT

PTH (pm/L)

200

175

150

125

100

75

50

25

0

LOWEST HIGHEST

COMPARISON OF HIGHEST vs LOWEST PTH FOR EACH PATIENT (n=18)

HIGHEST AND LOWEST PTH FOR EACH PATIENT

PTH (pm/L)

200

175

150

125

100

75

50

25

0

LOWEST HIGHEST

COMPARISON OF HIGHEST vs LOWEST PTH FOR EACH PATIENT (n=18)

808/18 CROSSED THRESHOLD FOR SURGERY/MIMPARA

HIGHEST AND LOWEST PTH FOR EACH PATIENT

PTH (pm/L)

200

175

150

125

100

75

50

25

0

LOWEST HIGHEST

COMPARISON OF HIGHEST vs LOWEST PTH FOR EACH PATIENT (n=18)

808/18 CROSSED THRESHOLD FOR SURGERY/MIMPARA

RA target

30

14

Assay variations meant,in total,15 out of 18 patients (83%)would have required changes to

their treatment....

Assay variations meant,in total,15 out of 18 patients (83%)would have required changes to

their treatment....*2 at risk of ABD by lowest reading would have

had treatment increased by highest reading.

Assay variations meant,in total,15 out of 18 patients (83%)would have required changes to

their treatment....*2 at risk of ABD by lowest reading would have

had treatment increased by highest reading.

*5,on target by lowest reading would have had treatment intensified by highest reading

Assay variations meant,in total,15 out of 18 patients (83%)would have required changes to

their treatment....*2 at risk of ABD by lowest reading would have

had treatment increased by highest reading.

*5,on target by lowest reading would have had treatment intensified by highest reading

*8 would have had medical therapy by lowest

reading and surgery by highest.

JOLY ET AL. Am J Kidney Disease Apr 2008

“....up to 11 of 34 patients were classified in different (K/DOQI) categories with some assays....PTH variability caused by the nature of the assay...is large enough to potentially influence clinical decision making.”

PTH ASSAYS USED IN SCOTLAND

ASSAY

SIEMENS IMMULITE (RIE)SIEMENS CENTAUR (KIRKCALDY)ROCHE ELECSYS (DGRI) DIASORIN LIAISON (GRI)BECKMANS ACCESS (BORDERS)

PTH ASSAYS USED IN SCOTLAND

ASSAY

SIEMENS IMMULITE (RIE)SIEMENS CENTAUR (KIRKCALDY)ROCHE ELECSYS (DGRI) DIASORIN LIAISON (GRI)BECKMANS ACCESS (BORDERS)

NORMAL RANGE

1.2 -7.6 pmol/L 1.2 - 7.6 pmol/L 1.6 - 6.9 pmol/L 1.0 – 6.5 pmol/L 1.2 – 7.6 pmol/L

On average the Diasorin Liason assay gave readings 2.38 times lower than the Siemens Immulite assay ,yet clinicians using the 2 different methods are aiming for almost exactly the same target range (13-26 pmol/L vs 15-30 pmol/L) .

RENAL ASSOCIATION –PTH“The target range should increase from the normal range with CKD stages 1-3,to between the top of the normal range and twice the normal range for stage 4 CKD, and to between 2 and 4 times the upper limit of normal in CKD stage 5,not on dialysis. These targets should apply to transplant patients also.”(Good Practice)

“In dialysis patients the target range for PTH should be between 2 and 4 times the upper limit of normal for the PTH assay used.”(Good Practice)

WHERE ARE WE NOW?

“…measuring PTH and ‘an unknown amount of other things which have an undetermined effect’,…..using machines that measure different amounts of the different things,in a way that we can’t quantify,yet use the same normal range…..aiming to achieve a target based on work done with an old assay that is no longer used!”

SO,WHERE FROM HERE?

SO,WHERE FROM HERE?

• Confirm study findings with a larger population.

SO,WHERE FROM HERE?

• Confirm study findings with a larger population.

• Calibrate machines with plasma from CRF patients

SO,WHERE FROM HERE?

• Confirm study findings with a larger population.

• Calibrate machines with plasma from CRF patients

• Introduce correction factors for each assay.

SO,WHERE FROM HERE?

• Confirm study findings with a larger population.

• Calibrate machines with plasma from CRF patients

• Introduce correction factors for each assay.• Await automated 3rd generation PTH assay.

‘ So the answer isn’t 42 then?....’

“.......and DON’T even get me STARTED on Calcium!!!!!!”

DIASORIN LIAISON CONSISTANTLY GAVE THE LOWEST PTH

MEASUREMENT.

DIASORIN LIAISON CONSISTANTLY GAVE THE LOWEST PTH MEASUREMENT.

IN SUMMARY -

METABOLISM OF PTHPTH

NH2

1

COOH

84

ACTIVE END INACTIVE END

DIASORIN LIAISON CONSISTANTLY GAVE THE LOWEST PTH MEASUREMENT.

HIGHEST READING WAS CONSISTANTLY FROM ONE OF THE SIEMENS ANALYSERS.

HIGHEST AND LOWEST PTH FOR EACH PATIENT

PTH (pm/L)

200

175

150

125

100

75

50

25

0

LOWEST HIGHEST

COMPARISON OF HIGHEST vs LOWEST PTH FOR EACH PATIENT (n=18)

808/18 CROSSED THRESHOLD FOR SURGERY/MIMPARA

15 2/18 CROSSED LOWER TREATMENT THRESHOLD

DIASORIN LIAISON CONSISTANTLY GAVE THE LOWEST PTH MEASUREMENT.

HIGHEST READING WAS CONSISTANTLY FROM ONE OF THE SIEMENS ANALYSERS.

RANGE OF ASSAY VARIATION WAS FROM 1.4 FOLD TO 4.2 FOLD.

METABOLISM OF PTHPTH

NH2

1

COOH

84

ACTIVE END INACTIVE END

1 34NH2 COOH

35 84

DIASORIN LIAISON CONSISTANTLY GAVE THE LOWEST PTH MEASUREMENT.

HIGHEST READING WAS CONSISTANTLY FROM ONE OF THE SIEMENS ANALYSERS.

RANGE OF ASSAY VARIATION WAS FROM 1.4 FOLD TO 4.2 FOLD.

HIGHER PTH LEVELS WERE NOT ASSOCIATED WITH THE LARGER VARIATIONS.

ALL 17 OTHER PATIENTS SHOWED

1.4 -4.2 FOLD DIFFERENCE

BETWEEN THE LOWEST PTH MEASUREMENT AND THE HIGHEST PTH MEASUREMENT

METABOLISM OF PTHPTH

NH2

1

COOH

84

ACTIVE END INACTIVE END

1 34NH2 COOH

35 84

NH2 COOH 1 6 7 15 34 84

METABOLISM OF PTHPTH

NH2

1

COOH

84

ACTIVE END INACTIVE END

COOH35 84

LIVER

RE-ENTERS CIRCULATION.

EXCRETED BY KIDNEYS

METABOLISM OF PTHPTH

NH2

1

COOH

84

ACTIVE END INACTIVE END

1 34NH2 COOH

35 84

LIVER

ELIMINATED IN LIVER RE-ENTERS CIRCULATION.

EXCRETED BY KIDNEYS