Q & A

June 2003

Richard A. Savage, MD

Q. Can DNA analysis be done on cremated remains?

A. The question of DNA identification of cremains or partially incinerated remains comes up surprisingly often for those who perform DNA typing on skeletal remains.

It is very difficult to completely incinerate human remains. Commercial crematoriums typically expose bodies to 2,000°C for two hours. Under these conditions, the ashes will not yield DNA. Most remains recovered from building fires, however, are not totally incinerated and will contain DNA.

DNA within bone is very stable and can withstand temperatures of several hundred degrees or more for short time periods. DNA cannot be recovered, however, when a bone becomes calcined. Calcined bone, often described as porcelain-like, has been reduced to its white or blue mineral constituents, indicating all organic material has been destroyed.

Scorched and blackened bones may or may not yield DNA and generally should be tested. Many DNA analysts have been surprised to find a typable result when it appeared that the bone was not worth testing.

DNA is destroyed by progressive fragmentation. This may result in some DNA identification markers being successful when others are not, so one may be left with a partial set of DNA identity markers. In such cases, the discriminatory power may be reduced, yet a likelihood of identity established.

Most DNA identity testing involves short tandem repeat analysis that is performed on the nuclear (chromosomal) DNA, but in these cases mitochondrial DNA testing may be required. Mitochondrial DNA tests are more likely to be successful because a cell may have only one copy of nuclear DNA but hundreds or thousands of copies of mitochondrial DNA in the cytoplasm of the cell. Mitochondrial DNA testing, however, is less discriminating, more expensive than short tandem repeat nuclear DNA analysis, and performed by only a few laboratories.

Victor Walter Weedn, MD, JD
Principal Research Scientist
Director of Biotechnology and Health Initiatives
Carnegie Mellon University, Pittsburgh

Q. Many articles state that the half-life of low-molecular-weight heparin is longer than that of unfractionated heparin, but they do not give a specific figure for the half-life. What is the half-life of LMWH? LMWH is monitored by the anti-Xa inhibition test. What is the principle behind the chromogenic anti-Xa test?

A. The answer to your first question is clear-cut. The half-life of low-molecular-weight heparin is three to four hours.^1,2
Your second question requires a longer explanation. The heparin assay depends on the inhibition of factor Xa. A 1998 article in the Archives of Pathology and Laboratory Medicine³ summarized the heparin assay very well, stating:

Methods for determination of the functional activity of heparin are based on the ability of heparin to accelerate the inhibition of a standard concentration of an activated coagulation enzyme, such as factor Xa or thrombin, in the presence of enough AT [antithrombin] to complex all available heparin. The ease, accuracy, and precision of these assays have been improved by the development of enzyme-specific chromogenic and fluorogenic substrates. The signal generated is proportional to the amount of residual factor Xa (or thrombin) remaining after neutralization by the AT-heparin complex and is thus inversely proportional to concentration of heparin. The signal may be measured by endpoint or kinetic techniques. Functional heparin assays should be simple, reliable, reproducible, highly sensitive, and easily adapted to automation. These assays also should be relatively easy to standardize among laboratories; however, there is still variability reported. Some of this variability may be due to preanalytical differences. Many of the newer multipurpose coagulation instruments can perform heparin assays concurrently with other routine coagulation assays without requiring major instrument adjustments or reagent preparation. The chromogenic assays based on factor Xa inhibition have also been shown to be effective for the measurement of low-molecular-weight heparin.

In the United States, the APTT remains the most commonly used test for monitoring unfractionated heparin. On the 2002-CG-2B proficiency testing challenge, fewer than 200 laboratories reported results for a heparin assay. The heparin assay is most frequently used only in uncommon settings when the APTT will not suffice. LMWH does not usually need to be monitored, but when monitoring is necessary, only the factor Xa inhibition method can currently be used.

References

1. Laposata M, Green D, Van Cott EM, et al. College of American Pathologists Conference XXXI on laboratory monitoring of anticoagulant therapy: the clinical use and laboratory monitoring of low-molecular-weight heparin, danaparoid, hirudin and related compounds, and argatroban. Arch Pathol Lab Med. 1998; 122: 799–807.
2. Hirsh J, Levine MN. Low molecular weight heparin. Blood. 1992;79:1–17.
3. Olson JD, Arkin CF, Brandt JT, et al. College of American Pathologists Conference XXXI on laboratory monitoring of anticoagulant therapy: laboratory monitoring of unfractionated heparin therapy. Arch Pathol Lab Med. 1998;122: 782–798.

John D. Olson, MD, PhD
Professor and Director of Clinical Laboratories
Department of Pathology, University of Texas
Health Science Center, San Antonio
Chair, CAP Coagulation Resource Committee

Q. How can the Centers for Medicare and Medicaid Services justify reimbursing for blood and components at a rate below that charged by the hospital’s supplier?

A. First, let’s note that even under the fee-for-service payment system that predated inception of the Medicare prospective payment system, or PPS, in 1983, Medicare and other third-party payers typically paid only about 80 percent of costs, with the remainder covered by the patient.

CMS uses the same methodology to reimburse hospitals for blood products and services under the PPS as it does to reimburse hospitals for other products and services. Medicare does not reimburse hospitals for the cost of acquiring blood products per se. Instead, Medicare pays flat amounts for specific types of hospital discharges, defined by diagnosis related groups. Each DRG payment is intended to represent the bundle of costs involved in caring for a patient whose stay is categorized under that DRG. The payment level for each of the more than 500 DRGs is a function of a base payment rate for each hospital and the relative weight of each DRG, both of which are updated annually. (Hospital costs are just one component used to update a national standardized payment amount, which is subject to area- and hospital-specific adjustments to yield a hospital’s base payment rate.)

The DRG weights are recalibrated each year to reflect relative changes in the resources required to provide care among the respective DRGs. This recalibration does not increase overall Medicare payments; it simply provides a way to reallocate Medicare payments in the inpatient PPS. Here’s the kicker for blood payments: These DRG weights are based on the charges, not costs, that hospitals report to Medicare each year. The Medicare inpatient PPS is based on the assumption that reported charges are good proxies for the relative resource use among DRGs. CMS only knows what hospitals report to the agency. If charges are not reported or if the charge amounts for a product or service are low, then the charges on which DRG payments are based will be underrepresented. (The DRG updates generally lag behind the charge data by two years.)

CMS recently reported that only 48 percent of hospitals billed for one or both of the blood-related cost centers in their Medicare reports to CMS. Our analysis found great disparities in how often hospitals bill for blood products and services and in the charges they use when blood is billed. On average, the hospital markup of charges over costs for blood products and services is less than half the markup for other hospital products and services. Together, these factors significantly underrepresent the costs to hospitals of blood products and services in Medicare’s determinations of DRG weights and the reimbursement for blood-intensive DRGs, accordingly.

CMS has acknowledged the importance of paying appropriately for blood products and services. The Department of Health and Human Services Advisory Committee on Blood Safety also has endorsed appropriate payment rates, specifically in reference to the outpatient payment system. Medicare is keenly aware that many of its billing rules are complex and that this may have contributed to inadequate hospital coding and billing.

Medicare appears to be interested in simplifying these rules and informing hospitals how to implement them. The health care sector welcomes such efforts by CMS. At the same time, however, it is unlikely that Medicare will establish a special mechanism to pay for blood products and services under the PPS. The accounting for blood-related costs in the Medicare PPS will not improve until CMS obtains more complete and accurate charge data from hospitals. CMS should, therefore, work with hospitals, blood collection and banking organizations, and other stakeholders to provide clear, comprehensive guidance for coding and billing of blood products and services.

Clifford Goodman, PhD
Vice President, Senior Scientist
The Lewin Group, Falls Church, Va.