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Warm transport at 37°C
What guidelines and the current body of research on the pre-analytical handling of cryoproteins reveal
When diagnosing cold agglutinins, cryoglobulins and cryofibrinogen, it is not solely the laboratory that determines the quality of the result – but rather the temperature control throughout the process.
If such a sample cools below 37°C during collection, transport or storage, the temperature-sensitive proteins precipitate prematurely and are lost for analysis. This results in false-negative findings, delayed diagnoses and the need for repeat tests.
This page summarises the evidence from international guidelines and the current body of research regarding the necessity of consistent transport at 37°C.
What the guidelines require
Maintaining a constant temperature of 37°C is not merely a recommendation from individual laboratories, but is enshrined in current national and international guidelines:
Onkopedia guideline „Autoimmunhämolytische Anämien (AIHA)“ (Röth et al., DGHO, as at 2026):
The current German guideline issued by the DGHO states that cold agglutinins cause agglutination of red blood cells – particularly if blood is not collected directly into pre-warmed containers. With regard to plasma separation in cases of cold agglutinin disease, the guideline stipulates that this must be carried out strictly at 37°C.
German overview of cold agglutinin disease (Röth et al., 2025):
The overview in Innere Medizin (Internal Medicin) states that samples must be stored and transported at 37–38°C until the plasma or serum has been separated from the cells – this is essential for the correct determination of the thermal amplitude.
International consensus on AIHA (Jäger, Barcellini, Broome, Röth, Berentsen et al., 2020):
The recommendations of the First International Consensus Meeting (Blood Reviews) define warm sample handling for cold antibodies as part of standardised diagnostic procedures.
ASH overview of cold agglutinin disease (Berentsen, 2025):
Warm pre-analytical procedures are cited as a fundamental prerequisite for accurate titres and thermal amplitudes.
BSH guideline on primary AIHA (Hill et al., 2017):
The UK guideline describes the diagnostic algorithm, including the thermal amplitude test, for which the temperature chain must be maintained.
Key message of the pre-analytical best practice guidelines (Sargur et al., 2010):
The sample temperature should be maintained at 37°C until the serum has separated. The most common source of error is false-negative results due to the loss of cryoprecipitate during transport and storage.
What the research reveals
Over 40 publications deal with pre-analytical temperature control. Three findings form the solid core:
In practice, the cold chain is rarely unbroken:
In an assessment of 140 laboratories (UK NEQAS), only 36 % adhered to the standard procedure involving processing at 37°C (Vermeersch et al., Clinical Chemistry 2008). Around two-thirds were therefore operating outside the recommended conditions.
The problem affects a significant number of patients:
In the largest cohort to date (Lyon), 1,675 out of 13,439 patients tested were found to be cryoglobulin-positive – under strict pre-analytical conditions, specifically to avoid false-negative results (Kolopp-Sarda et al., Arthritis & Rheumatology 2019).
Furthermore, the cold chain does not only affect specialised tests. Cold precipitation also distorts routine parameters – such as automated blood counts and the quantification of monoclonal proteins (Cunningham et al., 2026; Cunningham & Brandt, 1992).
Active temperature control drastically improves sample quality:
In a transport study, the proportion of samples arriving at the laboratory at 37–38°C rose from 34 % to 95 % as soon as a temperature-controlled transport device was used (Nahm et al., Clinical and Vaccine Immunology 2012). The difference was not due to the laboratory, but solely to the temperature control during transport.
Cryoglobulins: the most common indication for the 37°C warm chain
Whilst cold agglutinin disease is rare, cryoglobulin testing is one of the tests routinely requested – including in connection with hepatitis C infections, autoimmune diseases and lymphoproliferative disorders, and frequently when cryoglobulinaemic vasculitis is suspected. It is precisely in this context that pre-analytical temperature control is particularly crucial.
The mechanism is clear:
cryoglobulins are immunoglobulins that precipitate reversibly at temperatures below body temperature and redissolve when warmed. If a blood sample cools down before the serum has been separated, the cryoglobulins precipitate and are lost with the blood clot – resulting in a false-negative result or an abnormally low cryocrit. The best-practice recommendation is therefore as follows: collection in pre-warmed tubes, transport, clotting and centrifugation must all be carried out at 37°C until the serum has been separated (Sargur et al., 2010).
The scale in figures:
In the largest cohort to date, 1,675 out of 13,439 patients tested were cryoglobulin-positive (Kolopp-Sarda et al., 2019) – the data were collected under strict pre-analytical conditions, specifically to avoid false-negative results. At the same time, in an evaluation of 140 laboratories, only 36 % adhered to the standard temperature-controlled procedure (Vermeersch et al., 2008). The shortcoming therefore rarely lies in the analytical procedure itself, but rather in the sample’s journey to the laboratory.
Transport maintained and documented at a constant temperature of 37°C therefore ensures that a negative cryoglobulin result is indeed negative – and not the result of a sample that has become chilled.
What laboratories require in practice
This requirement is not limited to guidelines and studies – it is set out as a binding stipulation in the laboratories‘ publicly available test specifications. Anyone having cold agglutinins tested will regularly find the requirement for transport to be carried out at a constant warm temperature specified there.
For example, the list of analyses from Dr Fenner & Colleagues Laboratory (Hamburg), entry „Cold agglutinins“ (as at 12 January 2026): The sample required is „10 ml of whole blood (warm)“. The pre-analytical section states that blood samples must be kept „warm (approx. +37°C) from the time of collection until they arrive at the laboratory“. And specifically regarding sample transport: „Whole blood must be transported at approx. +37°C“.
This means that transport at 37°C becomes an operational requirement for referring doctors, hospitals and courier services – not merely a recommendation, but a prerequisite for obtaining usable test results. This is precisely where the practical need arises: the requirement exists, but in many places there is no standardised, verifiable means of ensuring compliance with it in day-to-day transport operations.
Why passive solutions have their limitations
The literature documents a number of improvised and passive methods for maintaining a temperature of 37°C: phase-change containers (Nahm 2012), simple incubator vessels (Veerasubramanian 2018), thermos flasks filled with warm water (Basile 2016) or hand-warmed containers (Wheeler et al., 2020).
These demonstrate two things: the need for a closed thermal chain is undisputed in professional circles – and the solutions used to date face two limitations.
Passive systems cannot actively provide additional heating over longer distances or in cooler environments, and they do not provide evidence that the temperature was actually maintained throughout.
It is precisely this seamless evidence that ISO 15189 increasingly requires as a controlled, documented transport process (Nybo et al., 2019; Vermeersch et al., EFLM Consensus 2021).
SteadyCube* was developed to make this very requirement a practical reality in everyday transport:
The device actively maintains the temperature within a range of 37°C (± 1°C) – even in cool environments and without a mains power supply – and records the temperature history.
In this way, it helps laboratories and institutions to comply with and demonstrate adherence to the warm chain as described in guidelines and the literature.
Why do samples for cold agglutinins and cryoglobulins need to be transported at 37°C?
This is because the relevant proteins precipitate at temperatures below 37°C. If the sample cools down before serum separation, the cryoprecipitate is lost and the result might be a false negative (Sargur et al., 2010).
What do the guidelines say about the transport of samples for cold agglutinins?
The current DGHO Onkopedia guideline (Röth et al., 2026) states that blood should be collected directly into pre-warmed containers and that plasma separation must be carried out strictly at 37°C.
The specialist review by Röth et al. (2025) also recommends that samples be stored and transported at 37–38°C until the plasma or serum has been separated from the cells.
How often is the 37°C rule actually applied in practice?
In an assessment of 140 laboratories, only 36 % adhered to the standard procedure involving processing at 37°C (Vermeersch et al., 2008).
Does active temperature control during transport offer a measurable benefit?
Yes. In a transport study, the proportion of samples arriving at the correct temperature of 37–38°C rose from 34 % to 95 % as soon as a temperature-controlled device was used (Nahm et al., 2012).
Are the laboratories actually requesting transport by road?
Yes. Test request forms specify „whole blood (warm)“ and „transport at approx. +37°C“ for cold agglutinins – for example, at the Dr Fenner & Colleagues laboratory (as of 2026).
Warm transport is therefore an operational prerequisite for a usable result.
Why isn’t a well-insulated carrier enough?
A passive box only stores heat until it is used up.
It cannot actively reheat the sample and does not provide evidence of the actual temperature profile – both of which are increasingly required by ISO 15189 as a documented process.
Sources
A complete list of 44 references is available on request. Key sources cited on this page:
- Röth A, Feistritzer C, Höchsmann B, Panse J, Rosner A, Schrezenmeier H, Schubert J, Sormann S, Waldvogel-Abramowski S, Zeerleder S. Autoimmunhämolytische Anämien (AIHA). Onkopedia-Leitlinien, DGHO, Stand 2026.
- Röth A, Borchert K, Dorn C, et al. Kälteagglutininerkrankung. Die Innere Medizin 2025;66:986–996.
- Jäger U, Barcellini W, Broome CM, Röth A, Berentsen S. Diagnosis and treatment of autoimmune hemolytic anemia in adults: Recommendations from the First International Consensus Meeting. Blood Rev2020;41:100648.
- Berentsen S. Diagnosis and management of cold agglutinin disease. Hematology Am Soc Hematol Educ Program 2025;2025(1):295–304.
- Hill QA, Stamps R, Massey E, et al. The diagnosis and management of primary autoimmune haemolytic anaemia. Br J Haematol 2017;176(3):395–411.
- Sargur R, White P, Egner W. Cryoglobulin evaluation: best practice? Ann Clin Biochem 2010;47:8–16.
- Vermeersch P, Gijbels K, Mariën G, et al. A critical appraisal of current practice in the detection, analysis, and reporting of cryoglobulins. Clin Chem 2008;54(1):39–43.
- Kolopp-Sarda MN, Nombel A, Miossec P. Cryoglobulins today: detection and immunologic characteristics of 1,675 positive samples from 13,439 patients over six years. Arthritis Rheumatol 2019;71(11):1904–1912.
- Nahm MH, Chatham WW, Benjamin WH Jr. Device for carrying blood samples at 37 °C for cryoglobulin test. Clin Vaccine Immunol 2012;19(9):1555–1556.
- Nybo M, Cadamuro J, Cornes M, et al. Sample transportation – an overview. Diagnosis 2019;6(1):39–43.
- Vermeersch P, Frans G, Meyer A, et al. How to meet ISO 15189:2012 pre-analytical requirements? EFLM WG-PRE consensus. Clin Chem Lab Med 2021;59(6):1047–1061.
- Dr Fenner & Colleagues MVZ Laboratory. List of tests – Cold agglutinins. As at 12 January 2026.
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*Product information: SteadyCube is a technical device designed for the active temperature stabilisation of samples during transport. It is not a medical device within the meaning of EU Regulation 2017/745 (MDR). The device does not perform any diagnostic analysis or medical assessment and is not a substitute for laboratory medical processes.
