T R A N S F U S I O N C O M P L I C A T I O N S

A new tool for communicating transfusion risk information

D.H. Lee, I.E. Paling, and M.A. Blajchman

ew disciplines of medicine have attracted the media attention that transfusion medicine has at- tracted recently. This is largely because many in- F dividuals, tragically, were infected with human im-

munodeficiency virus through the transfusion of contami- nated clotting factor concentrates and blood components. As a result of the intense legal and media scrutiny this brought on, the public has developed a heightened aware- ness of transfusion-related risks.’

While tremendous efforts have been made to ensure the safety of the blood supply and to quantitate the residual risks to the recipients of blood components, little effort has been made by the transfusion medicine community to communicate information about such risks effectively to patients and to the public. Rather, much of the lay public’s knowledge of transfusion-associated risks comes from the media. It is on this basis that the lay public and most pa- tients make judgments and decisions about their medical care and that of their families.

Effective communication of information about trans- fusion-associated risks is important for decision making at several levels. For the patient, it is needed to ensure that consent for blood transfusion is truly informed. Physicians who prescribe blood components not only must under- stand the probabilities of the various transfusion-associ- ated risks, but also should be able to explain those prob- abilities to their patients in a fashion that the patient can comprehend and put into perspective. At the societal level, effective communication of information about transfusion- associated risks may influence public opinion and policy.

In Canada and most other countries, public confidence and trust in the blood system have waned in recent years.

From the Departments of Pathology and Medicine, McMaster University; and the Canadian Red Cross Society Blood Services, Hamilton, Ontario, Canada; and the Center for Cooperative Learning, College of Medicine, University of Florida, Gainesville, Florida.

July 17, 1997, and accepted July 30, 1997. Received for publication March 31, 1997; revision received

TRANSFUSION 1998;38:184-188.

Blood donations have decreased, and individuals have be- come increasingly hesitant about receiving transfusions, even when they are recommended by their physicians. While it is recognized that emotions such as trust, dread, and outrage (qualitative risk estimates) are powerful deter- minants of risk perception,2t3 it remains essential that pa- tients and the lay public have accurate quantitative risk information with which to form their own opinions about the acceptability of a particular risk.

The loss of trust in the blood system may hinder com- munication about risks, yet this is the very situation in which such communication is needed most, if that trust is to be regained.4

Effective risk information communication is more dif- ficult and complex than is generally appre~iated.~ The fra- gility of communication about scientific and technical is- sues to the lay public is illustrated by the observation that judgments made by the public frequently incorporate in- accurate factual information.6 Comprehending the likeli- hood of low-probability events and their relative frequen- cies is particularly difficult.’ For example, many individuals do not understand that a risk of is 100 times greater than a risk of lo-’. Another difficulty has been the lack of a simple framework that would help the public conceptual- ize and compare the quantitative risk estimates of various hazards. This article describes one approach that might prove useful for improving the communication of the prob- ability of transfusion-associated risks to the patient or lay- person.

MINIMIZING THE CHANCE OF BEING MISUNDERSTOOD: THE PALING

PERSPECTIVE SCALE To address the problem of risk information communication in transfusion medicine, we introduce the Paling Perspec- tive Scale (0 John Paling 1992).8 The Paling Perspective Scale is protected by copyright law but may be used with- out charge providing the intellectual property rights of the originator are noted by defining the format as “The Paling Perspective Scale 0 John Paling 1992.” Digital copies of the basic chart are freely available from the author. Previously,

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this instrument has been used to communicate informa- tion on the risks of industrial and environmental hazards. It displays both the absolute and relative risks of various hazards in a manner that is intended for ready understand- ing by the public and the media. It is a simple scale that can be used to express the risk of any hazard relative to any other. Integers from -6 (a probability of 1 x 10-l2) to +6 (a probability of 1) span the horizontal axis. Each unit inter- val from -6 to +6 represents a log,, difference in probabil- ity (Fig. 1). Error bars can be introduced for a particular risk estimate, or, when a range of risk estimates exist for a par- ticular hazard, a horizontal bar or line can be used to span the range of estimates. In this way, the reader is provided with an appreciation of the degree of uncertainty of such estimates.

Effective zero (0 on the Paling Scale) Zero on the scale represents a probability of lo4, because for most hazards a risk of one in a million or less is consid- ered safe (effectively, zero risk). It has been argued that when the risk of death from exposure to industrial and en- vironmental substances is less than lo4 per year, such risks are insignificant, because this is the risk level that most in- dividuals are willing to accept in their personal and daily ac- tivities? Similarly industrial or environmental hazards with a risk of death of 10” or greater are generally viewed as un- ac~eptable.~ Hazards with risks between lo4 and 10” fall within a large grey zone in terms of acceptability. The En- vironmental Protection Agency of the United States generally sets its regu- lations to keep risks below to 10-6.8 Similarly, the Food and Drug Administration regards as safe a food additive (or its breakdown product) that increases the lifetime risk of can- cer by less than Risks of this magnitude are considered too small to be of regulatory concern. Thus, for the purpose of communicating the magnitude of rare risks to the layper- son, lo4 has been defined by Paling as, effectively, zero risk.8 Risks that fall in the negative (<lo4) portion of the Paling Scale have, for practical pur- poses, a negligible likelihood of ever occurring.

Home base (0 to +2 on the Paling Scale) One of the objectives of the Paling Scale is to define a range of risks for the common hazards of daily life that the public understands and is comfortable accepting (Fig. 2). Many serious haz-

4 4 4 -3 -2 -1 0 +l +2 +3 +4 +s +(I

I I 1 PROBABILITY

R u n p ~ s e W ~ J o h n ~ l o o Z

Pig. 1. The Paling Perspective Scale.

ards carry risks of approximately +2 on the Paling Scale (lo4). “Home base” thus refers to the portion of the scale from 0 to +2 (lo4 to lo4). For common household hazards such as stairs, toys, and lawnmowers, the risks of non-life-threaten- ing injuries are an order of magnitude greater, spanning +2 to +4 on the scale. Figure 3 shows the annual risks of injury associated with various household consumer products, es- timated from the number of emergency room-treated cases in the United States.I6 Such events still do not affect most people. The events that most individuals are likely to experi-

- 6 - 5 - 4 - -

I I I I I I I I I I I I I I I I I

RISK DECREASING I I I I I I I

I Annu: risk ofldeath d m accidints at hdme n

Annual risk of being killed in a motor vehicle accident in Canada l1

I I I I

Risk of mother dying during the birth of a single child l3

Annual risk of cancer from drinking one beer a day for 1 year l4

I I I I Annual risk of skin cancer. from living in hnver14

Point below which any risk from-a food additive is considered too small to be of regulatory concern for the US FDA I0

charbroiled steak once a week for a year l4 Annual risk of cancer from eating a

I Annual risk of being killed by lightning in Canada l1

E m m u Homebase -6 -5 4 -3 -2 -1 0 +I +2 +3 +4 +5 Paling perspective Scale @p John Paling 1992

Fig. 2. Risks with whlch the public is comfortable. This represents the extra risk of liv- ing in Denver (at higher altitudecompared to that of New York. FDA = Food and Drug Administration.

Volume 38, February 1998 TRANSFUSION 185

LEE ET AL.

Televison sets

Refrigerators, k e r s I I

-6 -5 4 -3 -2 -1 0 + I +2 +3 +4 +5 +6 I I I PROBABILITY

10-12 10-11 10-10 109 104 10-7 i c ~ 104 104 10-3 10-2 10-1 1

W I

I I I I I I I I I I I I I I I d

RISK DECREASING RISK INCREASING 5

Nails, carpet tacks

Bathtubs and showers

Home workshop power sds

Fig. 3. Annual risk of injuries in the home. Data are estimates based on the number of emergency room visits associated with consumer products in the United States in 1993.16

23:32)-and of being murdered-9.2 x or +1.96 on the Paling Scale (approx. lOOx greater) (Time 1993;Aug 23:32). Transfusion-associ- ated risks are compared to those of other medical procedures and inter- ventions in Fig. 6.The mortality asso- ciated with open cholecystectomy in two large studies was 0.17 percentz5 and 1.4 percent,z6 which placed this risk at +3.2 to +4.1 on the Paling Scale. The estimated annual risk of death attributable to oral contraceptive use ranges from 3 x 1 V (for nonsmoking 15- to 19-year-old females) to 1.35 x lo4 (for smokers aged 30-34).27 This corresponds to +0.5 and +2.1, respec- tively, on the Paling Scale. (These fig- ures are data gathered in the 1970s, at a time when the average estrogen dose was higher than that currently used; the current risk of death from oral contraceptive use may be consid- erably lower.)

SUMMARY An effective means is needed for communicating information on

ence are associatedwith risks of+3 (lo9) or greater. However, such risks involve voluntary activities that are not generally

transfusion-associated risks to patients and the public. For the patient, the probability of an adverse

dreaded or thought of as bekg hazard- ous.

USING THE PALING SCALE TO EXPRESS

TRANSFUSION RISKS The transfusion-associated risks that have been chosen for display on the Paling Perspective Scale are shown in Fig. 4. When the data were available, error bars were used to showthe data. With the Paling Scale, transfusion- associated risks can be compared with a person's risk of being a victim of violent crime or of dying in a mo- tor vehicle accident (Fig. 5). For ex- ample, the estimated risk of infection with human immunodeficiency virus from the transfusion of a unit of blood in the United States (prior to p24 an- tigen testing) was approximately 1 in 500,000, or +0.3 on the Paling S ~ a l e . ~ ~ ~ * ~ Readers can compare this to the annual risk in the United States of a woman's being raped-8.34 x lo4, or +2.92 on the Paling Scale (ap- prox. lOOOx greater) (Time 1993;Aug

-6 -5 4 -3 -2 -1 0 + I +2 +3 +4 +5 +6 I I I PROBABILITY

1 1 ~ 2 1 1 ~ 1 10-10 109 104 10-7 104 105 10.4 10-3 10-2 10-1 1 I 1 I I I I I I I I I

I I I I h RISK DECREASING

Emcuu - 6 - 5 4 3 - 2 - 1

RISK INCREASING > I i r & ' B a t h from transfusion 17.1B

in j iry 19

Sepsis per PC unit 20.21

I I I I

+I +2 +3 +4 +5 +6 Pallng Perspective Scale @ John Paling 1992

Fig. 4. Estimated transfusion-associated risks per unit. PC = platelet concentrate; HBV = hepatitis B virus; HCV = hepatitis C Virus; HlV human immunodeficiency virus; HTLV = human T-cell lymphotmpic virus. C W , span of range of risk estimates; --.--,emor bars for a risk estimate.

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-6 5 -4 -3 -2 -1 0 +I +2 +3 +4 +5 +6

I I I I I I I I I I I

RISK DECREASING RISK INCREASING I I I I I I

I I I Ahual risk of a woman being raped'in the United Statesz4 1 I I

I I I I I I Annual risk of being murdered in Washington, DC" w : Annual risk of being killed in a motor vehicle accident in Canada l1

I I I I I I 1 1 1 1 1

Annual risk of being murdered in the United States"

Annual risk of being murdered in Canada I1 1. I

- 6 5 4 - 3 - 2 - 1 0 Pallng Pmpwllw Scale @John Pallng 1992

Fig. 5. Risk of violent crfme and motor vehicle accident (grey boxes) vs. transfusion- d a t e d risks (black boxes). .--., span of range of risk estimates; -W-, error bars for a risk estimate.

-6 5 -4 -3 -2 -I 0 +I +2 +3 +4 +5 +6

I I I I I I I 1 I I I I

RISK INCREA

I Risk of death from open cholecystectomy ''a

I l l

1 1 1 1 1

Annual risk of death from oral contraceptive use (ages 30-34, smoker) I'

I Risk of death from general anesthesia

I I Annual risk of death from oral contraceptives

(ages 15-19, nonsmoker) ''

=k

I l l I Rlsk of HIV per unk of Mood (belore p24 antigen testing)=* 1

I I Ell~cUvazem H u n e k w

-6 4 -4 -3 -2 -1 0 +I +2 +3 +4 +S +6 Pallng paspectw Scale @p John Paling 1992

Fig. 6. Other medical risks (grey boxes) vs. transfuslon-assoclated risks (black boxes). W-W, span of range of risk estimates; --C, error bars for a risk estimate.

event is essential for the effective implementation of the in-

UG - I

simple and instructive tools with which to visually communicate both absolute and relative risk; however, properly designed studies are needed to determine the effectiveness of such instruments. It also remains to be determined whether risk percep- tion and responses to risk can be al- tered by using such an approach. It is time to address such issues, as this approach may indeed be an advance in transfusion medicine.

Note added in proof The paling Perspective Scale was

recently used to put the relative risk of various opthalmologic procedures into per~pective.'~

1.

2.

3.

4.

5.

6.

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7. Zeckhauser RJ, Viscusi WK. Risk within reason. Science

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AUTHORS

David H. Lee, MD, FRCP(C), Clinical Scholar and Research Fel- low, Department of Pathology, McMaster University.

John E. Paling, PhD, Faculty member, Center for Environ- mental and Human Toxicology, University of Florida, Gainesville, FL.

Red Cross Society and Professor, Departments of Pathology and Medicine, McMaster University, 1200 Main Street West, HSC 2N34, Hamilton, Ontario, Canada UIN 325. [Reprint requests]

Morris A. Blajchman, MD, FRCP(C), Medical Officer, Canadian

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