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Calibrating Longitudinal eGFR in Patience Records Stored in Clinical Practices Using a Mixture of Linear Regressions [email protected] ICPR 2012 Norman Poh Simon de Lusignan Dept of Computing Faculty of Electronics and Physical Sciences Clinical Informatics Research Group Faculty of Economics, Business and Law University of Surrey United Kingdom

Calibrating eGFR

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Calibrating Longitudinal eGFR in Patience Records Stored in

ClinicalPractices Using a Mixture of

Linear Regressions

[email protected] 2012

Norman Poh Simon de Lusignan

Dept of ComputingFaculty of Electronics and Physical Sciences

Clinical Informatics Research Group

Faculty of Economics, Business and Law

University of SurreyUnited Kingdom

® Norman Poh 2

MotivationBiomedical signal is under- and irregularly

sampled and very noisy due to circardian rythme, assay methods, and confounding factors, among others.

Challenge: Finding signal from noiseOur objective: correct for structural noise

due to assay methodsInnovation: blindly distinguish the assay

methods using mixture of regression.Result: Successfully applied to calibrating

estimated Glomerular Filatration Rate (eGFR)

® Norman Poh 3

Problem statement

Serum creatinine

eGFR lab reporting(original)

eGFR lab reporting

(Gold standard)

Since 1990’s 2006 20102006-2009Report

ing m

easu

res

eGFR not used

Serum creatinine

eGFR calibrated to the Gold standardeGFR lab reporting

(Gold standard)

Since 1990’s 2006 20102006-2009Report

ing m

easu

res

Not distinguishable from each other

Example of data across patients (without calibration)

4

eG

FR=

est

imate

d G

lom

eru

lar

filt

rati

on r

ate

Eff

ect

iveness

of

kidney f

unct

ions

® Norman Poh 5

Sample results for one patient (original data)

Phase 0 Phase 1Phase 2

Phases 0, 1 and 2 are found via mixture of

linear regression

Both time-series are

indistinguishable

® Norman Poh 6

Calibrated to Phase 1

Phase 0 Phase 1Phase 2

Non calibrated eGFR obtained from Serum

Creatinine

calibrated eGFR to Phase 1 (green

points)

® Norman Poh 7

Calibrated to Phase II

Phase 0 Phase 1Phase 2

calibrated eGFR to

Phase 1 (red points)

® Norman Poh 8

Results (across all patients)Non-calibrated eGFR Calibrated eGFR

® Norman Poh 9

A functional representation

𝑐

X𝑔𝑆 X𝑔

𝐿

𝑔𝐿eGFR

Serum Creatinin

e(SCr)

Self-calculated Lab-calculated

X𝑐❑

𝑀𝑀𝐷𝑅𝐷

𝑀𝑢𝑔𝑆

Obtained from health record

Calculated variable

𝑀 𝑙𝑎𝑏

CF = confounding factorsGiven

We can deduce:

𝑈𝑛𝑘𝑛𝑜𝑤𝑛

Input data : a time-series of and .