Everything a PCP Needs to Know About Lab Testing (Rheum & Otherwise) PSVMC MEDICAL GRAND ROUNDS May 20, 2014 Richard Wernick, M.D

Everything a PCP Needs to Know About Lab Testing

(Rheum & Otherwise)

PSVMC MEDICAL GRAND ROUNDSMay 20, 2014

Richard Wernick, M.D.

Testing for Rheumatic Disease:A (PCP) Consumer’s Guide - Outline

• Synovial fluid analysis• RF/a-CCP• ANA/a-DS DNA & a-Smith• ESR/CRP• Temporal artery bx• ANCAs

Testing for Rheumatic Disease:A (PCP) Consumer’s Guide - Outline

• Synovial fluid analysis• RF/a-CCP• ANA/a-DS DNA & a-Smith• ESR/CRP• Temporal artery bx• ANCAs

• Bayes’ for PCPs• Spectrum effect• Reliability

Conflicts of Interest

• Industry• Financial• Personal

A Case of Acute Monoarthritis(File #1141) : “ZZ”

• 50 y/o M rock drummer• 3 d severe pain & swelling left knee• PMH – MI, DM-2, STDs, ETOH, cigs• Meds – simva, metformin, prn oxy/Ambien• PE – tender, warm, swollen knee; obese

Acute Monoarthritis: Differential Diagnosis

Inflammatory• Gout• Pseudogout• Bacterial• (DFKA “Reiter’s”)

Non-inflammatory• Internal

mechanical derangement

• Avascular necrosis• Hemarthrosis• Osteoarthritis

Acute Monoarthritis: Differential Diagnosis

Inflammatory• Gout• Pseudogout• Bacterial• (DFKA “Reiter’s”)

Non-inflammatory• Internal

mechanical derangement

• Avascular necrosis• Hemarthrosis• Osteoarthritis


• 50 y/o M rock drummer• 3 d severe pain & swelling left knee• PMH – MI, DM-2, STDs, ETOH, cigs• Meds – simva, metformin, prn oxy/Ambien• PE – tender, warm, swollen knee; obese

• Which test(s)? CBC, uric acid, SF, X-ray . . .• Discuss

Synovial Fluid Analysis: The 5 Tests

Gout Psgt BactWBC% polys+Gram stain+C&S+Crystals



20 K 20 K >50 K



20 K75

20 K75

>50 K>90



20 K75

Rare

20 K75

Rare

>50 K>90

65% (Ø GC)



20 K75

RareRare

20 K75

RareRare

>50 K>90

65% (Ø GC)≥95% (<10% GC)



20 K75

RareRare

80-90%

20 K75

RareRare~70%

>50 K>90

65% (Ø GC)≥95% (<10% GC)

5-10%



20 K75

RareRare

80-90%

20 K75

RareRare~70%

>50 K>90

65% (Ø GC)≥95% (<10% GC)

5-10%

+ LRs for bacterial: WBC <25 K – 0.32 >50 K – 7.7 >100 K – 28

(Rat’l Clin Exam ‘07)

Bayes’ for PCPs

• Sensitivity = % pts with disease who test positive (the way they should)

• Specificity = % pts without disease who test negative (the way they should)

• FP rate = 1- specificity• TP rate = sensitivity

Bayes’ for PCPs (2)

• Post-test probability depends on– Sensitivity– Specificity– Pretest probability

• As the sensitivity 100%, post-test prob 0 if negative– SNOut

• As the specificity 100%, post-test prob 100% if positive– SpPIn

Bayes’ Theorem for Calculating thePosttest Probability of Disease

Probability of disease if test is positive = P(D+)P(T+/D+) P(D+)P(T+/D+) + P(D-)P(T+/D-)

Probability if test is negative = P(D+)P(T-/D+)

P(D-)P(T-/D-) + P(D+)P(T-/D+)

MSU Crystals

Synovial Fluid Analysis Miscellany

• When to tap? Bugs or crystals still in DD?• Clotting falsely lowers WBC

– So does IR saline insertion• A dry tap does not exclude effusion• A negative G stain can’t r/o septic etiology• Crystal analysis not so reliable


• 50 y/o M rock drummer• 3 d severe pain & swelling left knee• PMH – MI, DM-2, STDs, ETOH, cigs• Meds – simva, metformin, prn oxy/Ambien• PE – tender, warm, swollen knee; obese• SF pos for urate crystals• Rx’d with IA TAC 40 mg

The “Diamond-Shaped Algorithm”

Test

Positive Negative

Management (Rx, education, . . .)

(eg, serum uric acid/CBC for ZZ)

Pitfalls in Testing: Reliability

• Reproducibility, precision• Prerequisite for widespread use of a test• Most important for subjective or

unstandardized tests• Gap between research lab & community

– Are community labs concordant?– Measured by Kappa (K) for categorical

results– K=0-chance; <0.4-poor; 0.4-0.7-fair; >0.7-

good

A Case of Acute Polyarthritis (File #777): “Polly R”

• 32 y/o F PCP• 6 days of pain & swelling PIPs, MCPs,

wrists and knees• PMH – Ø• SH – single, wine, recreational weed, 4+

travel• Meds – prns• PE – tender, swollen jts

Acute Polyarthritis: Differential Diagnosis

Symmetric (5)• RA• SLE• Viral (parvo, hep B,

HIV)• Lofgren’s• PMR

Asymmetric

• (4) I.D.ish Bacterial SBE Lyme RF

• (3) Sp-A “Reiter’s”

Psoriasis IBD

• (2) Crystal Gout

Pseudogout


• 32 y/o F PCP• 6 days of pain & swelling PIPs, MCPs, wrists

and knees• PMH – Ø• SH – single, wine, recreational weed, 4+

travel• Meds – prns• PE – tender, swollen jts

• What workup?

Which Test(s) Would You Order for Polly R (acute poly)?

1) ANA, reflexive2) ANA, quantitative3) RF & a-CCP4) ESR &/or CRP5) Tap/SF analysis6) Lyme titer

Vote for one or more now !

Acute Poly Tests

ANA reflex ANA quant RF/CCP ESR/CRP SF Lyme0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

83%

22%

58%

87%

15%10%

Does Polly R Have Lupus if ANA + ?

1000 clones pretest = 10%

100 SLE 900 Non-SLE

95% TP 5% FP

95 TP 45 FP

Posttest Prob = 95 = 68% 95 + 45

Does Polly R Have Lupus if ANA + ?

1000 clones pretest = 10%

100 SLE 900 Non-SLE

800 RA 100 Misc 95% TP

30% FP 5% FP

95 TP 240 FP 5 FP Posttest Prob = 95 = 28%

95 + 240 And if ANA - ?

Does Polly R Have MI if TROPONIN + ? 1000 clones pretest = 10%

100 MI 900 Non-MI

800 PE 100 Misc 95% TP

30% FP 5% FP

95 TP 240 FP 5 FP

MI Posttest Prob = 95 = 28% 95 + 240

And if Trop - ?

Pitfalls in Testing: Spectrum Effect (Bias)

• Variability in test sensitivity or specificity in different patient subgroups or clinical settings

• e.g.’s of specificity spectrum effect– ANA FP in 5% young normals, but 15%

>65 1/3 RA

– RF FP in 5% young normals, but 15% >65 75% hep C

• e.g.’s of sensitivity spectrum effect– UTI and dipstick– MS & MRI

Likelihood Ratios (LR)

LR(+) = TP rate (sens) LR(-) = FN rate (1-sens) FP rate (1-spec) TN rate (spec)

• Posttest odds = Pretest odds x LR

• The further from 1, the greater the impact on prob

• e.g.: If ANA sens = 95% & FP rate = 5%, LR (+) = 95/5 = 19

- but if FP rate = 30%, LR (+) = 95/30 = 3

- if ANA neg, LR (-) = 5/70 = 0.07 (SNOut)

Anti-Nuclear Antibody (ANA): The Basics

• Screen for many possible Abs v. NAs• IFA v. EIA (screen v. reflexive)• Sensitivity (SLE) ~ 95% (at 5% FP cut pt)• FP rate varies – Spectrum Effect (Bias)

– ~1/3 RA, 15% >65, AI thyroid disease, meds, . . .• Supports dx of SLE if prior prob reasonable• Better at R/O than R/I

– Chronic poly + ANA = RA• Reliability (reproducibility) issues• $65 for quantitative screen• The charge for reflexive?

ANAs: The Basics (2)

• Anti-DS DNA sens = 50%, spec >95%• Anti-Smith 25% >95%

– R/I > R/O• “Reflexive ANA”? (a-DNA, Sm, RNP, Ro, La,

Blah, Blah, Blah)– Charge = $752.50

• What is the FIRST stage of testing for SLE?

ANAs: The Basics (2)

• Anti-DS DNA sens = 50%, spec >95%• Anti-Smith 25% >95%

– R/I > R/O• “Reflexive ANA”? (a-DNA, Sm, RNP, Ro, La,

Blah, Blah, Blah)– Charge = $752.50

• What is the FIRST stage of testing for SLE?– CBC & UA

Rheumatoid Factor (RF): The Basics

• a-IgG Fc• Sens (RA) = 70% (at 5% FP cut pt)• FP rate (spec) varies

– ~ 1/3 SLE, 15% >65, 2/3 Hep C• Supports RA Dx if pretest prob reasonable• Small % with +RF have/will get RA• Reliability (reproducibility) issues• Worthless without arthritis (PE)• $60

Anti-Cyclic Citrullinated Protein (a-CCP):The Basics

• Citrulline is an a.a., modified arginine residue• Sens (RA) 70%, spec (in rheum clinic) 95%• 34% of RF neg “RA” pts• Predicts persistence of early inflammatory arthritis

– OR = 38 at 3 yr f/u– OR = 10 for new erosions over 5 yrs (3.4 for +RF)

• But also in 1/4 a-CCP neg pts & not in 1/5 a-CCP+

• It’s ok to do both RF & a-CCP if RA suspected• $49


• 32 y/o F PCP• 6 days of pain & swelling PIPs, MCPs, wrists and knees• PMH – Ø• SH – single, wine, recreational weed, 4+ travel• Meds – prns• PE – tender, swollen jts

• ANA 1:160, neg a-DS DNA & a-Smith• RF 1:160, neg a-CCP• Naproxen 500 mg b.i.d.• Resolved over 3 wks

Questions?

The Sed Rate (& CRP): Facts, Fancy & Fiction

• Facts– Cheap, quick & reproducible– RBC fall in 1 hr (mm)– Function of RBC aggregation– with inflammation, tissue injury– >30 in 98% GCA, >80% PMR, 50% RA– >100? - ?90% prob of dxable disease– CRP more direct, changes faster– CRP and ESR may be discrepant

Nl peopleDiseased people

The Sed Rate (& CRP): Facts, Fancy & Fiction (2)

• Fancy– Follow in GCA, PMR– CRP better– Increase with normal aging

• Fiction– If >100, think GCA (TB, MM)– Normal R/O PMR– Increase implies illness

ANCA: Facts, Fancy & Fiction

• Facts– Serologic marker for pauci-immune

necrotizing vasculitides• WG, MPA, C-S, drug-induced

– IFA: c-ANCA & p-ANCA (nonspecific)– ELISA: a-PR3(c) & a-MPO(p)– Sensitivity (c,a-PR3) 80-90%, spec >98%

for WG– Sensitivity if localized– a-MPO in 70% MPA

ANCA: Facts, Fancy & Fiction (2)

• Fancy–Replaces need for bx–Predicts flare

• Fiction–Reliable–p-ANCA helpful

Medical Decision-Making by Thresholds

100

C. Likelihood _____ Treat of disease(%)

B._____ Test

A. 0

Which Diagnostic Strategy is Better?The 4 Determinants

1.Sensitivity2.Specificity3.Cost ($ & morbidity)4.Reliability

A Case of Recurrent Herpes Labialis in a 24 y/o Musician (“Ritchie W”)

• Is he more likely a piano or a tuba player?

piano

tuba

The Musician with Recurrent Herpes Labialis (oral)

piano+ herpes

tuba + herpes

Tuba or Piano Player—The Representativeness Heuristic

A Case of Recurrent Herpes Labialis in a 24 y/o Musician (“Ritchie W”)

• Is he more likely a piano or a tuba player?• The question was NOT “Do tuba players

get more herpes labialis than piano players”

• Human brains substitute an easier, yet wrong question

• The representativeness heuristic

A Case of a Positive ANA

• Joan Smith has a positive ANA at 1:320• 3% of normal women have such an ANA• What can we say about Joan and her ANA?


• Joan Smith has a positive ANA at 1:320• 3% of normal women have such an ANA• What can we say about Joan and her ANA?• “There is a 3% chance this occurred by

chance” ?



chance” ?• “There is a 97% chance Joan has SLE” ?



chance” ?• “There is a 97% chance Joan has SLE” ? • “If Joan does NOT have SLE, there is a 3%

chance of getting this result”.

Multiple Testing Error

• A 31 y/o F with polyarthritis x 1 wk, macular rash x 2 days

• CXR (n=?) - possible opacity left base• RF slightly positive, a-CCP neg• Nl/neg CBC (n=≥6), CMP (n=20), UA (n=5?),

ANA, IgM a-parvo, Lyme titer, uric acid, APLA panel (n=6?), ANCA (n=2), C3/C4/CH50– Alk phos 132

• Nl hx (n=?) and PE (n=?) otherwise

Multiple Testing Error (2)• Normal range for most continuous tests = mean ±

2 SDs of healthy controls → 5% FP rate• FP rate may be higher in competing diseases• Chem 20 – 5% FP x 20 = 1 FP/normal

– 40% nls pass, some have > 1 FP• ~ studies & endpoints

– Try to minimize, prespecify primary endpoints– Likelihood of true pos ↑ if . . .

• More abnl• ↑ prior prob• Biologically plausible• Higher specificity• Fewer tests done

(Rheumatologic) Lab Testing for PCPs: Conclusions

• Optimal diagnostic testing is difficult– even more so with rapidly progressing disease, meter

running• Anticipate and avoid tests that lead to a diamond algorithm• Estimate prior probability; avoid “base case neglect”• SNOut, SpPIn• Don’t confuse sensitivity with NPV, specificity with PPV• Beware spectrum effect

– Sens and/or spec may vary• In rheum, few tests are diagnostic

– Observation over time may be the best test (uncertainty!!)– Reliability issue– H&P much more helpful

Troponin in MI ScattergramTr

opon

in

:.

. . . . … . . . . . . . … … .. .

(3)

(2)

(1)

MI Controls

. .

.

.

.

.

. … .

.

.

. … .

.

.

. … . .

.

. .

:

.

.

The Case of the Increasingly Sensitive Troponin

• Sensitivity 83% (4th gen cTn T, Roche) 95% (HS)• Specificity 93% 80%• PPV 72% 50%• NPV 97% 99%• Not specific for type of myocardial injury

– HF, PE, demand ischemia, sepsis, myocarditis, KD, . . .• ↑ sens → ↓ spec

– Ok for ED, not for inpatient• Prob of MI in a typical U.S. chest pain observation unit=<5%• HS cTnT above MI threshold in 15% U.S. CP pts; only 2% had

MI (Januzzi, Circ ‘10)– ↑ cost/tests, anxiety

de Lemos. JAMA 2013:2262-9

A Case of Amaurosis Fugax (File #533): “George C”

• 75 y/o M with 15 minutes of R eye blindness yesterday

• PMH – DM2, PAD, ↑ BP• SH – s/p cigs• Meds – ASA 81, metformin, lisinopril, simva• PE – wnl• Lab – ESR 83• Workup ?

– 1) carotid US, 2) TA Bx, 3) CRP, 4) TA color duplex US, 5) 25-OH vit D

ESR ↑ with Aging

The Temporal Artery Biopsy:Facts, Fancy & Fiction

• Facts– Skip lesions– Take 4 cm– Sens (GCA) ? 75%– 2nd side adds 3% sens– Most will be negative– Hypoechoic halo (US) sens=69%, spec 82%

(Karassa’05)• Only helps by r/o if low prob; reliability ?

• Fancy - a negative bx rules out GCA• Fiction - Can wait 2 wks to bx after pred Rx

A Case of Amaurosis Fugax (File #533): “George C”

• 75 y/o M with 15 minutes of R eye blindness yesterday

• PMH – DM2, PAD, ↑ BP• SH – s/p cigs• Meds – ASA 81, metformin, lisinopril, simva• PE – wnl• Lab – ESR 83• Pred 60 mg/d• TA Bx positive 3 days later

A Case of Pulmonary-Renal Syndrome (File #277): MM

• 50 y/o F with 2 wks of cough & worsening SOB• PMH – neg• PE – diffuse crackles, T 100.8• Hgb 12.1, WBC 7.8 (nl diff), platelets 535K• Creatinine 4.3, UA-2+ pro, 30-40 RBC, 10-15

WBC• CXR – diffuse hazy opacities• Kidney Bx pending• DDx? • Wkup?

A Case of Pulmonary-Renal Syndrome (File #277): MM (2)

• Workup? (vote for one or more)1) ESR/CRP2) ANCA by IFA3) ANCA by EIA4) ANA5) Anti-GBM6) Lung Bx

ESR/CRP ANCA,IFA ANCA,EIA ANA a-GBM Lung Bx0%

20%

40%

60%

80%

100%

120%

63%

90%

80%

100%

85%

25%

Pulm-Renal Syndrome Tests

A Case of Pulmonary-Renal Syndrome (File #277): MM(3) - Test Results

• ESR 63• c-ANCA 1:640• ↑ anti-Pr3• ANA 1:80, homogeneous• Neg a-GBM• DIF of kidney Bx – “pauci-immune”• Dx – GPA (WG)• Pred + cyclo

Questions?

Documents

Everything a PCP Needs to Know About Lab Testing (Rheum & Otherwise) PSVMC MEDICAL GRAND ROUNDS May 20, 2014 Richard Wernick, M.D