Publication Highlight: Norwegian Study Confirms Feasibility of Self-Sampling with Capitainer®B for Routine Monitoring of Kidney Transplant Recipients

A recent study from Norway found that Capitainer’s volumetric dried blood spot microsampling device Capitainer®B is suitable for routine monitoring of kidney transplant patients. Importantly, the study revealed equal sampling success and analytical quality for samples collected with Capitainer®B, whether sampling was performed by healthcare staff in a hospital setting or by the patient themselves at home. Inclusion of self-sampling into the aftercare regimen is expected to make follow-up care more convenient and comfortable for this patient group, while easing the burden on healthcare services.

According to the Global Observatory On Donation and Transplantation, the kidney is the most commonly transplanted organ with more than 90,000 transplantations performed globally each year.

Recent figures from the U.S. alone reveal that more than 106,000 people are on the national transplant waiting list with 92,000 of these awaiting a kidney. This is a large and complex patient group that is expected to grow in size as people live longer, and the prevalence of obesity, diabetes and hypertension increase, all of which lead to higher rates of chronic kidney disease.

Those fortunate enough to receive a donor kidney in time require life-long follow-up care including therapeutic drug monitoring (TDM), to avoid graft rejection and opportunistic infections, to ensure optimal kidney function and compliance to prescribed medication, and to prevent long-term complications of immunosuppressive drugs.

Patients are very closely monitored in the early post-transplant phase, with several check-ups weekly. Such regular follow-ups place significant demands on transplant clinics to deliver appropriate care and can also be such a burden for the patients themselves that it negatively impacts aftercare compliance.

A patient-centric approach to improve aftercare in kidney transplant recipients

Volumetric microsampling devices allow finger-prick sampling of capillary blood, and are gaining traction for TDM, diagnostics, and serology testing. For example, recent studies have demonstrated success with using Captainer’s volumetric dried blood spot (DBS) microsampling device Capitainer®B for TDM of lithium in the treatment of psychiatric disorders and anti-epileptic drugs, as well as the detection of clinically-relevant ceramide biomarkers of cardiovascular disease.

Self-sampling enables greater flexibility for patients who need regular follow-up and reduces the burden on healthcare systems. DBS microsampling carries additional benefits, such as ambient, non-hazardous transport (since dried blood is not considered a biohazard) and stability during long-term storage. These advantages can help to promote better access to healthcare in remote areas as well as improve patient compliance to treatment and aftercare.

Recognising the need for more flexible kidney transplant monitoring, researchers and clinicians at University Hospital Oslo and University of Oslo, both in Norway, developed analytical methods for microsamples and compared the clinical performance of two volumetric devices for DBS sampling to monitor tacrolimus (an immunosuppressive drug), as well as creatinine and haemoglobin (markers of kidney health).

Tacrolimus, creatinine and haemoglobin form a standard panel that is required for monitoring of kidney transplant patients, and a self-sampling test for all three markers is expected to reduce the number of follow-up visits and improve the overall aftercare experience for this patient group.

Kidney transplant monitoring: volumetric DBS microsampling vs. venous blood sampling

The study involved 25 adult kidney transplant patients of Oslo University Hospital over a 6-month period in 2022 and sought to compare Capitainer®B and one other volumetric device with conventional, i.e., venous blood sampling.

Patients who took part in the study were monitored on an out-patient basis in the early phase (2-8 weeks) after kidney transplantation. Patients were shown how to use the self-sampling devices via written instructions, verbal instructions and video tutorials.

Prior to this study, previous studies had investigated non-volumetric and volumetric microsampling methods for combined monitoring of immunosuppressants and creatinine in kidney transplant patients, but none of these addressed how finger-prick self-sampling performs compared to assisted self-sampling by healthcare staff. Therefore, the current study by Vethe et al. included 3 different microsampling scenarios which were carried out on separate days, before and after dosing with tacrolimus:

  1. Finger-prick microsampling performed by healthcare staff (venous blood also taken for comparison)
  • Finger-prick microsampling performed by patient under supervision (venous blood also taken for comparison)
  • Finger-prick microsampling performed patient at home, alone

All microsamples were analysed for tacrolimus, creatinine and haemoglobin, and compared with data from routine analysis methods for venous blood samples. The agreement between measurements in finger-prick microsamples and liquid venous samples was the primary outcome of the validation.

The researchers also sought to compare differences between the two volumetric devices, both of which were used at all sampling time points, as well as the outcome of self-sampling vs. sampling performed by healthcare staff. Their findings were published last month in the British Journal of Clinical Pharmacology (1).

Capitainer®B demonstrated superior reliability and consistency with self-collected samples

Overall, for tacrolimus monitoring, sampling with either volumetric device led to reliable trough concentrations and AUC predictions regardless of sampling scenario. These parameters are used to inform healthcare staff about how much drug is present in a patient’s blood and if/when they should receive an additional dose.

However, for creatinine and haemoglobin, only samples collected with Capitainer®B yielded reliable measurements, and this was verified in an external validation study performed in a real-life clinical setting with a separate group of kidney transplant patients.

Let’s take a closer look at the results:

For tacrolimus measurements and predicted AUC for the 25 transplant recipients included in the main study, the proportions within ±20% difference were similar for both volumetric devices tested, at 79-96%. For creatinine and haemoglobin, Capitainer®B yielded superior proportions within ±15%, at 92-100% and 93-100%, compared for 79-96% and 67-92% for the other device.

As mentioned above, the sampling success rate was consistent for Capitainer regardless of sampling scenario (92-96%), whereas the other device showed 72-88% and 52-72% success rates with samples collected by healthcare personnel and the patients themselves, respectively.

Importantly, this study illustrates that when Capitainer®B was used, sample quality was consistent regardless of whether patients collected their own samples at home or healthcare staff were involved. This finding is critical for successful implementation of self-sampling in kidney transplant monitoring, but also holds promise for other applications, since consistent sample quality is a prerequisite for all quantitative tests.

The first patient-centric approach to monitoring kidney transplant patients

The study by Vethe et al. is unique in demonstrating the utility of Capitainer®B to monitor the full standard panel of drugs/markers required in kidney transplant patients. Other studies have investigated microsampling for TDM of immunosuppressants, but those have mostly focused on technical aspects or reducing the burden on laboratory staff. Because other studies did not incorporate the full testing panel, they had no real impact on the number of patient visits to healthcare settings.

In contrast, Vethe et al. have taken a patient-centric approach by testing the full standard panel to monitor kidney transplant patients. Their results highlight the feasibility of including self-sampling in the early stages of kidney transplant monitoring, which should reduce the number of hospital visits, simplify the follow-up process and improve quality of life for this patient group.


  1. Vethe NT, Åsberg A, Andersen AM, Skauby RH, Bergan S, Midtvedt K. Clinical performance of volumetric finger-prick sampling for the monitoring of tacrolimus, creatinine and hemoglobin in kidney transplant recipients. Br J Clin Pharmacol. 2023 Aug 3. doi: 10.1111/bcp.15870. PMID: 37537150.


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