# Presentation: 916119

## Red Cell In Vivo Recovery and Survival Studies

- Richard J. Davey, MD
- The Methodist Hospital, Houston TX
- Blood Products Advisory Committee
- May 1, 2008

## Evolution of Labeling and Evaluation Criteria

- 1947:  Ross proposes 70% red cell survival at 24 hours as a minimum recovery
- 1950:  Gray and Sterling describe 51Cr as a red cell label
- 1967: Fisher describes 99mTc as a red cell label
- 1985:  Minimum survival raised to 75% following FDA workshop
- 1989:  AuBuchon refines use of 111In as a red cell label
- 1998:  Minimum survival ≥ 75%: SD ≤ 9% based on historical data
- 2004:  Current criteria based on historical data, BPAC

## Characteristics of an Ideal Red Cell Radiolabel

- Minimal preparative manipulation of red cells
- Specific for red cells
- Nontoxic to the cell
- Nontoxic to the recipient
- No metabolism by red cells
- No elution from the cell
- Radioactive half-life appropriate for the duration of the study
- No relabeling of other cells

## Characteristics of Commonly Used Red Cell Radiolabels

_**Characteristic**_**	****51**_**Cr **_**	****	****99m**_**Tc**_**	****	****111**_**In**_
- Half-life		27.7 days	6.0 hours	2.8 days
- Elution		1% day	4% hour	4% day
- Major 	γ-photon	320 keV	140 keV     173,247 keV
-     emissions
- Suitable for imaging     No		Yes		Yes

## Technical Steps for Labeling Red Cells with 51 Cr 

- A suitable sample of red cells stored under experimental condition is chosen.  For autologous studies,
-      ~ 15ml is used.
- An amount of **51** Cr is used to insure minimum adequate counts throughout the study (~ 4000 counts/sample: 5 to 20 μCi)
- After incubation with test red cells, unbound **51** Cr is removed
- An appropriate standard is prepared for blood volume determination
- Labeled red cells are infused into a peripheral vein and exact volume of infused material is determined

## Technical Steps for Labeling Red Cells with 51 Cr

- Samples are drawn from opposite arm.  Several early samples are drawn for 100% survival determination.
- Samples counted in duplicate and corrected for elution.

## Early Loss of Labeled, Stored Red Cells After Infusion

## Zero-Time Determination by Direct Red Cell Mass Measurement  (99m Tc) and by Back-Extrapolation (51 Cr)

## Partial List of Red Cell Products Evaluated Using Red Cell Recovery Studies

- New plastics and plasticizers
- New anticoagulant/preservatives
- Filtration devices and leukoreduced products
- Irradiated red cells
- “Undercollected” red cell units
- Pathogen inactivation procedures
- Enzymatic removal of A and B antigens

## Effect of Prestorage Irradiation on 24-hour Posttransfusion Red Cell Recovery

-     	_Storage Interval_              21 Days1            28days1          42 Days2
-    	_Radiation dose_                 20 Gy                20 Gy             30 Gy
- 	              	  	  _Control  Irrad_.     _Cont.  Irrad_    _Cont.  Irrad_.
- Potassium  (mEq/L)       	   36.6      63.4      47.7    69.4     42.6    78.1
- ATP (μM/g Hb)	 	     3.6	    3.2         3.8     3.5        2.1      1.9
**RBC 24 hr recovery (%)****	****    90.4     82.2      85.0    80.7     78.4    ****68.5****   **
- 1. Friedman et al.  Transfusion 1991;31:50S
- 2. Davey et al.  Transfusion 1992:32:525-8

## Evolution of Labeling and Evaluation Criteria

- 1947:  Ross proposes 70% red cell survival at 24 hours as a minimum recovery
- 1950:  Gray and Sterling describe 51Cr as a red cell label
- 1967: Fisher describes 99mTc as a red cell label
- 1985:  Minimum survival raised to 75% following FDA workshop
- 1989:  AuBuchon refines use of 111In as a red cell label
- 1998:  Minimum survival ≥ 75%: SD ≤ 9% based on historical data
- 2004:  Current criteria based on historical data, BPAC

## FDA Requirements for Approval of Red Blood Cell Products

- Total 20 or more evaluable 24-hour recoveries
- Minimum two laboratories
- Sample mean ≥ 75%
- Sample standard deviation ≤ 9%
- One-sided 95% lower confidence limit for the proportion of successes must be >70% with success threshold for individual recovery ≥ 75%.
- A successful trial can have no more than 3 of 24 RBC recoveries below 75%
- Hemolysis < 1% at end of storage
- Comparison, control vs. test:  ATP, 2,3 DPG, pH, glucose, lactate

## The Problem With “Old” Blood

## Mechanisms of Morbidity and Mortality:  The Red Cell Storage Lesion

- _Storage Lesion_
-    Decreased 2,3 DPG
-    Increased rigidity
-    High PA I level			    Poor O2 transport
-    High CD 40			    Inflammation
-    NO depletion			    Thrombosis
-    Increase in IL-10
-    Decrease in TNF-α

## Depletion of 2,3 DPG

## Loss of RBC Deformability

## Storage Depletes RBC Nitric Oxide Bioactivity

## Outcomes:  Liberal vs. Restrictive Transfusions

- _Outcome Measure_         _Restrictive (_n=418)    _Liberal_ (n=420)   _*p  *__value_
- 				(Hb: 7.0-9.0)	        (Hb: 10.0-12.0)
**Death (# / %)**
-    30 day		    78 (18.7)		98 (23.3)	0.11
-    ICU			    56 (13.4)		68 (16.2)            0.29
-    Hospital		    93 (22.2)                   118 (28.1)           0.05
**Length of stay – days**
-    ICU			  11.0 ± 10.7                 11.5 ± 11.3          0.53
-    Hospital                         34.8 ± 19.5                 35.5 ± 19.4         0.58
- Hebert PC, et al.  New Engl J Med 1999;340:409.

## Factors Associated With Postoperative Morbidity Post-CABG

-   _**Variable**_**	****           **_**Odds Ratio**_**     **_**Upper CL**_**    **_**Lower CL**_**    **_***p ***__**value**_
**Transfusion**
-   PRBC, units		     1.73	         1.67            1.80       <.0001
**Preoperative**
-   Higher BMI		     1.05            1.04            1.07       <.0001
-   Abnormal LVEF                     1.62            1.33            1.98      <.0001
-   Peripheral vasc. disease       1.54            1.21            1.95        .0004
-   Previous stroke                     1.55             1.14            2.11       . 0051
- “Perioperative RBC transfusion is the single factor most reliably associated with postoperative morbid events”
- Koch GC et al.  Crit Care Med 2006;34;1608

- Hypothesis
- Serious complications and mortality after cardiac surgery may increase when red cell units are transfused after they have been stored for more than 2 weeks
- Patients underwent coronary-artery bypass grafting, cardiac-valve surgery, or a combination of the two procedures
- 6002 patients studied from June 30, 1998 to January 30, 2006
- All serious morbid events evaluated
- When blood was ordered for transfusion, the blood bank provided the oldest available matching unit for each request (FIFO)
- Median time of storage was 15 days

## Slide 22

## Conclusions

- Patients given older blood:
- Greater in-hospital mortality (2.8% vs. 1.7%, P < 0.004)
- More likely to need prolonged ventilatory support (9.7% vs. 5.6%, P<0.001)
- More likely to have renal failure (2.7% vs. 1.6%, P < 0.003)
- Increased sepsis (4.0% vs. 2.8%, P < 0.01)
- Increased multisystem organ failure (0.7% vs. 0.2%, P < 0.007)

## Red Cell Recoveries in Clinical Trials:  Where Should We Set the Bar?

- Technical labeling procedures are well established and performed by skilled laboratories
- Prudent to be cautious in liberalizing threshold value
- Do not want to set bar so **high**** **as to lead to unnecessary trial failures.  (67.3% historical success rate for liquid products @ 75% threshold value)
- Do not want to set the bar so **low**** **as to have almost 100% success.  (99.9% historical success for liquid products @ 67% threshold)
- Alternatives:
**70%** threshold value = 95.5% historical success (liquid storage)
**72 -73%** threshold value?
- Davey RJ.  Editorial.  *Transfusion*.  In press.