Complications associated with long-term dialysis therapy include anemia, chronic kidney disease–mineral and bone disorder (CKD-MBD), and electrolyte abnormalities. Management and treatment of these complications requires regular surveillance blood work for patients on dialysis therapy. More frequent blood work results in closer monitoring of patients; however, differences in laboratory testing volumes among institutions have not been associated with clinical outcomes in the general population.
Upgraded recommendations in clinical practice guidelines for patients on dialysis therapy for frequency of blood work vary between 1 and 3 months for the management of anemia and phosphate levels. Informal conversations with dialysis therapy providers in the United States reveal a 4-week interval for blood work in dialysis patients. However, according to Samuel A. Silver, MD, MSc, and colleagues, there have been no studies conducted to examine the optimal interval of routine blood work in patients receiving hemodialysis in relation to clinical outcomes.
The researchers conducted a retrospective interrupted time series at a tertiary hospital in Ontario, Canada, to test the hypothesis that there would be no difference in anemia or CKD-MBD target performance between 4-week (high frequency) and a 6-week (low frequency) blood work periods and that this effect could be sustained for more than 1 year. Results were reported in the American Journal of Kidney Diseases[2019.73(4):496-503].
The analysis was conducted from June 1, 2012, to December 31, 2015. Data on annual characteristics for adult patients receiving in-center hemodialysis at Kingston Health Sciences Center were obtained from the Canadian Organ Replacement Register. The hospital provided data on the total number of blood tests, both routine and nonroutine; data on achievement of clinical targets were obtained from the center’s electronic medical record (NephroCare).
The primary outcomes of interest were achievement of hemoglobin (10-12 g/dL) and phosphate (2.5-4.6 mg/dL) targets as recommended by the College of Physicians and Surgeons of Ontario and the Canadian Society of Nephrology. Secondary outcomes included use of erythropoietin, achievement of calcium (8.8-10.2 mg/dL) and parathyroid hormone (PTH; 94-462 pg/mL) targets, and all-cause mortality.
The high frequency (every 4 weeks) blood work period occurred from June 1, 2012, to March 23, 2014 (661 days). The low frequency (every 6 weeks) blood period occurred from March 25, 2014, to December 31, 2015 (647 days).
The number of prevalent hemodialysis patients increased from 344 to 422 between 2012 and 2105, representing 697 patient-years from June 1, 2012, to March 23, 2014, and 766 patient-years from March 25, 2014, to December 21, 2015. Patient characteristics and demographics remained similar over the study period, with a trend in later years toward older patients and greater use of central venous catheters.
Of the 344 prevalent hemodialysis patients in 2012, mean age was 63.7 years, 55.5% were men, 44.5% used a central venous catheter, and diabetes was listed as the primary cause of kidney disease in 39.5%. Of the 422 prevalent hemodialysis patients in 2015, mean age was 61.5 years, 58.8% were men, 46.9% used a central venous catheter, and diabetes was listed as the primary cause of kidney disease in 37.9%. The patient population ranged from 86.9% to 89.4% white and 4.8% to 6.2% aboriginal during the entire study period.
During the study period, the proportion of patients who achieved the recommended clinical targets for hemoglobin and phosphate was stable, with no measurements outside the control limits. Hemoglobin mean target achievement was 60% and phosphate mean target achievement was 46%. In late 2014/early 2015, two of three consecutive measurements for hemoglobin targets were more than two standard deviations from the mean; performance quickly rebounded to previous levels of 60%. There was no evidence of special cause variation in phosphate targets.
Average use of erythropoietin was 78% during the study period. In early 2015, as demonstrated by eight continuous observations below the mean, there was evidence of special cause variation with a decrease in erythropoietin use. Hemoglobin targets were stable during this period.
During the entire study period, the proportions of patients achieving the recommended calcium and PTH clinical targets were stable; there were no measurements outside the control limits. Mean achievement of calcium target was 48% and mean achievement of PTH target was 55%. During the 4-week blood work period, there was wide variation in mortality, with several points above the upper control limit and eight continuous observations below the mean. Following the switch to blood work at 6-week intervals, the hemodialysis unit mortality rate remained stable.
The researchers performed a cost subanalysis comparing 4-week intervals during 252 days (July 15, 2013, to March 23, 2014) with 6-week intervals during 252 days (March 25, 2014, to December 1, 2014). The costs of individual tests were based on the Ontario Schedule of Benefits for Laboratory Services in Canadian dollars: hemoglobin, $8.27; ferritin, $14.48; iron saturation, $17.58; serum calcium, $2.59; and serum phosphate, $2.59.
During the 252-day measurement 6-week interval period, there was less testing and lower costs across all available laboratory types. There were 529 fewer hemoglobin tests (cost savings of $4375), 575 fewer ferritin tests (cost savings of $8326), 592 fewer iron saturation tests (cost savings of $10,407), 283 fewer calcium tests (cost savings of $733), and 439 fewer phosphate tests (costs savings of $1137). The change to 6-week interval blood work would, on a yearly basis, save the 400-patient hemodialysis unit ~$6000 in hemoglobin tests, $12,000 in ferritin tests, $15,000 in iron saturation tests, $1000 in calcium tests, and $1600 in phosphate tests.
Study limitations included the inability to adjust for patient case-mix; the possibility that less frequent blood work changed absolute values or increased variability; not measuring all possible routine laboratory tests, clinical outcomes, and associated costs; changing the blood work intervals to 6 weeks rather than a longer period; lack of measurement in changes in patient behavior; and limiting the study to a single Canadian hemodialysis program.
In summary, the researchers said, “Our retrospective interrupted time series analysis of a regional hemodialysis program in Ontario, Canada, found that the proportion of patients who achieved recommended hemoglobin and CKD-MBD targets did not change after switching the routine blood work frequency from every 4 weeks to 6 weeks. The effects were sustained for more than 18 months and saved our program $85 per patient-year in laboratory costs. At the national level, cost savings from less frequent blood work could approach millions of dollars annually, but our results would need to be confirmed in different centers and across multiple clinical outcomes and include a more robust economic analysis. In the meantime, hemodialysis programs should reexamine their own blood work practices while more research is conducted to generate high-quality evidence to guide optimal routine blood work frequencies.”
Takeaway Points
- Researchers in Canada conducted a retrospective interrupted time series analysis to define the effect of changing the frequency of routine blood work in patients on hemodialysis therapy from 4- to 6-week intervals; outcomes of interest were achievement of recommended hemoglobin and phosphate levels.
- During the two study periods (high frequency, 4-week intervals: 6/1/12 to 3/23/14 and low frequency, 6-week intervals: 3/25/14 to 12/31/15), the proportion of patients who achieved recommended targets remained stable.
- The hemodialysis unit mortality rate remained stable, and reduction in frequency of blood work resulted in a saving of $85 per patient-year.