Alkaline phosphatase Laboratory Perspective

Professor William D Fraser Professor of Medicine University of East Anglia, Norwich, UK [email protected]

Disclosures – Prof. Fraser

 Unrestricted funding for assay development from Roche, Siemens, and IDS  Holds patents with IDS regarding assays in development  Consultant fees from Alexion Pharmaceuticals Alkaline phosphatase (ALP)

 A hydrolase enzyme (EC 3.1.3.1)  Removes phosphate groups from several molecules:  Proteins, nucleotides and alkaloids  Optimal activity in vitro in an alkaline environment1

1. Vroon DH and Israili Z. Alkaline phosphatase and gamma glutamyltransferase. In: Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston 1990. Alkaline phosphatase (ALP)

 In humans, the following isoenzymes1 are commonly detected:  Tissue non-specific ALP (liver, bone, kidney)  Intestinal ALP  Placental ALP  Germ cell ALP  Highest concentrations are found in liver, bone, placenta, intestine and kidney  Several techniques exist for the quantification of ALP and the isoenzymes

1. Whyte MP. Hypophosphatasia. In: Thakker RV, Whyte MP, Eisman J, Igarashi T, ed. Genetics of Bone Biology and Skeletal Disease. Amsterdam: Elsevier/Academic Press; 2013. Assessing total ALP concentration by enzymatic colorimetric methods

 Relatively cheap and fully automated

 Following the cleavage of PO4 groups from the substrates, molecules with specific quantifiable absorbance characteristics are generated, e.g.  Disodium p-nitrophenyl phosphate to p-nitrophenol  4-nitrophenyl phosphate to 4-nitrophenoxide  Zn and Mg are important co-factors required for the action of ALP in these reactions Buffers (amino alcohols):  Diethanolamine (DEA) Germany/Scandinavia  2-amino-2-methyl-1-proponol (AMP) IFCC/USA/France  HEDTA

O O O O O O- N N N O ALP Rearranges at + HOH + O P O- Zn Mg2+ alkaline pH pH 10.3 O- O O O

O P O- O P O-

O- O- 4-Nitrophenyl phosphate 4-Nitrophenoxide 4-Nitrophenoxide (colourless) (colourless (yellow, quinonoid form) benzenoid form) Rate of formation at 37C ALP (WEQAS Results)

Method N Mean CV, % Um ALP, 37°C Roche, AMP buffer IFCC 499 16.259 6.8 0.06 AMP, optimised to IFCC 379 19.707 12.8 0.16

Diethanolamine buffer, DEA 111 39.079 17.8 0.82

AMP, non-optimised 92 18.612 7.7 0.19 Ortho Viros MicroSlide Systems 89 26.132 8.5 0.29

Dade Dimension, AMP buffer 80 27.277 22.4 0.86

Other AMP kits 65 18.063 7.8 0.22

Tris/carbonate buffer, KA units 44 31.591 31.8 1.89 laboratories of Number AMP, optimised to NVKC/SFBC 6 21.167 8.5 0.92

Agappe – DGKC-SCE 4 45.000 28.7 8.08 Colorimetric 4 18.050 14.9 1.68 U/L AMP, reduced interference 4 16.500 6.1 0.63 N Mean CV, % Um SDP Exc. - Select - 2 20.500 3.4 0.62 A All methods 1372 19.705 25.1 0.17 1.80 164 AMP, optimised to IFCC 379 19.707 12.8 0.16 1.80 41

Siemens ADVIA 42 19.049 8.0 0.3 1.74 3 WEQAS: Wales External Quality Assessment Scheme 1200/1650/1800/2400 provider in the UK Detection of ALP

 The most common approach for isolating isoenzymes  Electrophoresis followed by specific substrate-staining methods Detection of bone-specific ALP  Specific antibody-employing immunoassays for bone ALP1  Measure activity of ALP  Measure the mass of the molecule  Disadvantages  Cross reactivity with liver ALP in ~3–16% of these assays2,3,4

1. Manufacturers Pack inserts (IDS, Oxford Biosystems). 2. Fraser WD. Data on file. 3. Gomez, et al. Clin Chem. 1995;41(11):1560-1566. 4. Broyles, et al. Clin Chem. 1998;44(10):2139-2147. Measurement of ALP

 Historically, the vast majority of ALP assays have been performed to investigate diseases in which ALP is increased  10–12% of the test results were due to abnormal liver function, vitamin D deficiency, metabolic bone disease (e.g. Paget’s disease)  As a result, less attention has been given to low ALP concentrations (0.4% of results)  ALP reference ranges may also contribute to the underestimation of the prevalence of low ALP Representative reference ranges for ALP (Europe and the USA) Specimen Age group/age Concentration or enzyme Concentration (SI Source activity units) Adult 36–92 U/L 0.5–1.5 µkat/L Merck [1] Serum Adult 30–120 U/L 0.5–2.0 nkat/L USA [2] Plasma Male Female ARUP [3] 1–11 m 70–350 U/L 70–350 U/L 1–3 y 125–320 U/L 125–320 U/L 10–11 y 150–470 U/L 150–530 U/L ≥20 y 40–120 U/L 40–120 U/L Plasma Neonate 73–391 U/L Europe [4] Infant 59–425 U/L 1–14 y 76–308 U/L 14–16 y 49–242 U/L Adult 30–130 U/L

1. Wians FH. Merck manuals. Available at http://www.merckmanuals.com/professional/appendixes/normal-laboratory-values/blood- tests-normal-values. 2. Kratz A, et al. N Engl J Med 2004;351:1548–63. 3. ARUP National Laboratory. Alkaline Phosphatase Isoenzymes, Serum or Plasma. Available at http://ltd.aruplab.com. 4. Sheffield children’s NHS foundation trust. Laboratory handbook. April 2014. Reference ranges

 A recent survey of 26 laboratories in the UK revealed:  The lower limit was stated as being zero (0) U/L by two laboratories  No gender-specific reference range by eight laboratories1  Often a lack of recognition that paediatric reference ranges are significantly higher than adult ranges

1. Fraser WD. Data on file held at the University of East Anglia. Canada: CALIPER

Age (years)

CALIPER: Canadian Laboratory Initiative on Paediatric Reference Intervals (http://www.sickkids.ca/caliperproject/index.html)

CALIPER

 CALIPER Cohort samples have been used to produce paediatric reference ranges for most of the major manufacturers machines/methods. (Adeli K) Survey of child and adolescent health: KiGGS ALP levels, boys • IFCC standard method (Hitachi 917)

KiGGS:a long-term study conducted by the Robert Koch Institute http://www.kiggs-studie.de/english/home.html Survey of child and adolescent health: KiGGS ALP levels, girls • IFCC standard method (Hitachi 917)

KiGGS:a long-term study conducted by the Robert Koch Institute http://www.kiggs-studie.de/english/home.html Representative reference ranges for bone ALP (Europe and the USA) Specimen Age group/age Concentration or Concentration (SI units) Source enzyme activity (conventional units) Serum Male Female ARUP [1] 6 m–2 y 31.6–122.6 µg/L 33.4–145.3 µg/L 3–6 y 31.3–103.4 µg/L 32.9–108.6 µg/L 7–9 y 48.6–140.4 µg/L 36.3–159.4 µg/L 10–12 y 48.8–155.5 µg/L 44.2–163.3 µg/L ≥25 y 6.5–20.1 µg/L Premenopausal female 4.5–16.9 µg/L/7.0–22.4 µg/L Male Female ARUP [2] 1–6 y 0–208 U/L 0–189 U/L 7–9 y 0–264 U/L 0–246 U/L 10–15 y 0–340 U/L 0–340 U/L 16–19 y 0–165 U/L 0–91 U/L Females ≥16 y and males ≥20 y 0–55 U/L 0–55 U/L

1. ARUP National Laboratory. Alkaline Phosphatase Isoenzymes, Serum or Plasma. Available at ttp://ltd.aruplab.com/Tests/Pub/0021020. 2. ARUP National Laboratory. Bone Specific Alkaline Phosphatase. Available at http://ltd.aruplab.com/Tests/Pub/0070053. Low ALP

 Several clinical conditions may result in a low ALP  An algorithm has been developed that should help to guide the investigation of a low ALP ALP lower than appropriate Review medical ALP decision reference range history for low ALP

Artefact algorithm EDTA, oxalate (blood transfusion) Confirm low on serum sample

Metal Protein Disease-associated Vitamin abnormality Post-cardiac surgery Drug effect

analysis calorie hypothyroidism, low vitamin C, B12, post liver transplant estrogen, low Zn, Mg, malnutrition hypoparathyroidism, B6, folate, ESRF bisphosphonate, high Cu severe anaemia excessive vitamin D osteodystrophy clofibrate, achondroplasia omeprazole, cretinism lansoprazole

Abnormal Total protein Measure TSH, Measure and Drug therapy investigate albumin PTH, FBC correct may unmask and correct Correct abnormality genetic cause abnormality for low ALP

Possible genetic cause for HPP ALP remains below reference range after PEA and PLP measurement correction of abnormality Genetic testing of ALPL

Non-biochemical tests radiology, ECG muscle studies ECG: electrocardiogram; ESRF: end stage renal failure; FBC: full blood count; PTH: parathyroid hormone; TSH: thyroid stimulating hormone Pathophysiology of HPP

ALP ATP PPi

Promotion of NPP1 hydroxyapatite crystal (ENPP1) formation Inhibition of Pi hydroxyapatite crystal Ca Bone mineralisation Formation Pi

HPP is characterised by accumulation of PPi, which suppresses hydroxyapatite crystal formation Alkaline phosphatase gene (ALPL)

 Over 280 known loss-of-function mutations in the alkaline phosphatase gene (ALPL)  Autosomal recessive versus autosomal dominant transmission determines the clinical severity

http://www.sesep.uvsq.fr/03_hypo_mutations.php Serum ALP activity in HPP

O = odontohypophosphatasia

Normal mean and range (± 2 SD mean) Children 166 (80–342); Adults 51 (28–91)

Whyte MP. In: Bilezikian JP, Raisz LG, Martin TJ, eds. Principles of Bone Biology. Vol 1. 3rd ed. San Diego, CA, USA, Academic Press. 2008;1573–98. Clinical Features of Hypophosphatasia Perinatal/Infantile  Severe Hypomineralisation/ Skeletal Deformities  Ricketic Type Lesions  Fractures  Respiratory Failure  Poor Feeding/Weight Gain/ Failure to Thrive  Hypotonia

 Vitamin B6 Responsive Seizures  Hypercalcaemia/Hypercalciuria/Nephrocalcinosis  Craniosynostosis Clinical Features of Hypophosphatasia Juvenile (6 months to 18y)

 Skeletal Deformities  Ricketic Type Lesions  Recurrent Fractures/Poor Healing Fractures  Low BMD  Short Stature  Muscle Weakness  Waddling gait  Premature Tooth Loss Adult Hypophosphatasia (≥18y)

. Liverpool 12 patients . Norwich 26 patients – Age 17-86 – 26 detected by biochemical testing after presenting with bone aches (16) joint pains (14) or recurrent fractures (10) – Low Total ALP in all cases (many (10) had abnormal ALP in childhood missed –used wrong reference ranges) – Family connections in 8 (cousins, uncle and niece, brothers) – Misdiagnosis: Multiple Sclerosis (2)

Symptoms

. Bone aches(18) . Fracture pain (6) . Joint aches (16), Osteoarthritis (14), Articular Chondrocalcinosis (3) . Abdominal Pain (9) . Joint Laxity, Recurrent Dislocation - especially younger female patients 17-34 y (5) • Difficulty with household tasks, concentrating, working (hairdressing x3)

An Adult Case – 86 y Old Female

PMH DHx . Asthma • Felodipine . Hypertension • Montekukast . Cholecystectomy • Steroid inhaler . 2 humeral # as child • Omeprazole . Also # x3 wrist, x2 ankle, • Mirtazapine left femoral • Bendroflumethiazide • Domperidone + erythromycin SH • Alendronic acid ( 8 months ) • Never smoked • Infrequent alcohol

Fracture History

. 2000 – FOOSH – smith’s right wrist

. 2006 – leg gave way - midshaft femur

. 2007 – Fall – 2nd metatarsal

. 2011 – Fall – left distal radius

. 5/2012 – Fall – right distal radius

Further Investigations

FBC U+E LFT LFT Bone Other

Hb 114 Cr 87 Bil 7 aCa2+ 2.44 TSH 1.59

MCV 95 eGFR 54 Tot Prot 62 PO4- 1.24 FSH 36.3

Wbc 5.5 Na 136 Alb 35 ALP 22 LH 15.9

Plt 273 K 3.5 ALT 14 Vit D - 42 Prolac 1397 Dexa Scan

. T score – 1.7 & Z score of 1.2 lumbar spine

. 21% increase since last scan in 2000 What can we learn from this case?

 Not all atypical femoral fractures are BP induced

 Always consider hypophosphatasia in these patients

 Do BPs bring out phenotype in previously subclinical hypophosphatasia? Treatment Pathophysiology of HPP

ALP ATP PPi

PEA Promotion of NPP1 hydroxyapatite crystal (ENPP1) formation Inhibition of Pi hydroxyapatite crystal Ca Bone mineralisation Formation Pi

HPP is characterised by accumulation of PPi, which suppresses hydroxyapatite crystal formation ALP substrates

 A lack or low activity of tissue non-specific ALP (TNSALP) results in accumulation of ALP substrates:

 Pyridoxal 5’-phosphate (PLP) Vitamin B6-responsive seizures  Pyrophosphate (PPi) Inhibits bone mineralisation, causing rickets or osteomalacia  Phosphoethanolamine (PEA)

PLP, PPi and PEA in HPP

 Measured by HPLC or tandem mass spectrometry or spectrophotometric methods  Poor sensitivity and specificity as a diagnostic tool  May help in a small number of cases  May be of value in following enzyme therapy, monitoring changes with treatment

HPLC: high-pressure liquid chromatography; PEA: phosphoethanolamine; PLP: pyridoxal 5´-phosphate Representative reference ranges for PLP, PO4 and 25-hydroxy vitamin D (Europe and the USA) Specimen Age Concentration or enzyme activity Concentration (SI units) Source group/age (conventional units) Pyridoxal–5'– Plasma 5–50 µg/L* USA [1] phosphate (PLP) 5–30 ng/mL 20–121 nmol/L USA [2] Phosphorus, inorganic Serum 3.0–4.5 mg/dL 0.97–1.45 mmol/L Merck [3] 3–4.5 mg/dL 1.0–1.4 mmol/L USA [2] Males Females [4] 0-11 months NA** NA** 1-4 y 4.3-5.4 mg/dL 8-13 y 4.0-5.2 mg/dL 16-17 y 3.1-4.7 mg/dL 3.1-4.7 mg/dL ≥18 y 2.5-4.5 mg/dL 2.5-4.5 mg/dL Phosphate, fasting Plasma Neonate 1.0–2.7 mmol/L Europe [5] Infant 1.1–2.4 mmol/L Child 0.8–1.9 mmol/L Adult 0.8–1.5 mmol/L 25-hydroxy vitamin D Serum 15–80 ng/mL 37–200 nmol/L Merck [3] (vitamin D3; 25- >20 ng/mL >50 nmol/L UK (NOS, USA hydroxycholecalciferol) IOM) Plasma 10–68 ng/mL 24.9–169.5 nmol/L USA [2]

1. Mayo Clinic, Mayo Medical Laboratories (http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/60295. 2. Kratz A, et al. N Engl J Med 2004;351:1548–63. 3. Wians FH. Merck manuals. Available at http://www.merckmanuals.com/professional/appendixes/normal-laboratory-values/blood-tests-normal-value. 4. Mayo Clinic. http://www.mayomedicallaboratories.com/test-info/pediatric/refvalues/reference.php. 5. Sheffield children’s NHS foundation trust. Laboratory handbook. April 2014.. Conclusions

 Biochemical measurement of ALP is relatively cheap and readily available  Reference ranges are extremely variable with age and gender  The lower limit of normal range is often poorly defined  Paediatric reference ranges are higher than adult  An algorithm for investigation of low ALP is valuable to ensure the correct diagnosis is made in all cases and appropriate therapy can be commenced