Coagulogram: what the test shows and why it matters for an athlete

A coagulogram is a set of laboratory tests that assess the blood's ability to clot and to dissolve clots in time. For most people this test remains a "hospital" one, but athletes need it more often than it seems: injuries, surgery, long flights, dehydration and especially hormonal pharmacology change the balance between bleeding and thrombosis. The editorial team explains what exactly a coagulogram measures and how to use its results wisely.

What the hemostasis system is

Hemostasis is the set of mechanisms that stop bleeding when a vessel is damaged and at the same time prevent blood from clotting where it should not. It consists of three links: the vascular one (spasm of the damaged vessel), the platelet one (the sticking together of blood platelets into a primary "plug") and the plasma, or coagulation, link, when a cascade of protein factors converts soluble fibrinogen into insoluble strands of fibrin.

In parallel, the anticoagulant system works — antithrombin, proteins C and S — as well as fibrinolysis, which dissolves the clot after the vessel has healed. A healthy body constantly maintains a balance between these processes. A shift in one direction means a tendency to bleeding, in the other — to thrombosis.

The classic scheme divides the cascade into an "extrinsic" pathway, triggered by tissue factor from damaged tissues, an "intrinsic" pathway associated with contact activation, and a common pathway that ends with the formation of thrombin. The modern cell-based model of hemostasis (Hoffman, Monroe) shows that in the body these pathways are closely intertwined and take place on the surface of cells, but laboratory tests are still conveniently interpreted according to the classic scheme.

A coagulogram mainly checks the plasma link. The platelet count is usually taken from the complete blood count, and their function is assessed by separate specialized tests that are not part of a standard coagulogram.

The main coagulogram indicators

The composition of a coagulogram differs between laboratories: there is a basic (screening) version and an extended one. The basic one usually includes prothrombin time with INR, aPTT and fibrinogen. The extended one adds thrombin time, D-dimer, antithrombin III, proteins C and S, lupus anticoagulant and other tests.

Prothrombin time (PT) reflects the work of the extrinsic and common pathways, in particular the vitamin-K-dependent factors. Because of differences in reagents, the result in seconds compares poorly between laboratories, so it is standardized as the international normalized ratio (INR). It is the INR that is used to monitor warfarin therapy. The Quick prothrombin is another form of expressing the same test, as a percentage.

The activated partial thromboplastin time (aPTT) assesses the intrinsic and common pathways. It is prolonged with a deficiency of factors VIII, IX, XI, with heparin therapy and in the presence of certain antibodies. Fibrinogen is the protein from which the clot is directly formed; at the same time it is an acute-phase protein, so its level rises with inflammation and after injuries.

D-dimer is a fragment of fibrin breakdown. It appears in the blood when a clot has formed in the body and begun to dissolve. Its normal result has high value: combined with a low clinical probability, it makes it possible to rule out deep vein thrombosis with great confidence (Wells et al., 2003). An elevated D-dimer, on the contrary, is nonspecific.

Why the test matters specifically for an athlete

Physical exercise itself temporarily activates both clotting and fibrinolysis. After intense or prolonged work, in healthy people these processes remain balanced, so regular training is generally associated with better cardiovascular health. Problems arise when other risk factors are added to the load.

The first such factor is dehydration. Thickening of the blood with heavy sweating, "cutting weight" in combat sports or long starts in the heat increases viscosity and promotes stasis. The second is prolonged immobility: flights to competitions, immobilization after injury, a cast, surgery on the knee or ankle joint. Lower-limb injuries and surgery remain one of the most frequent causes of thrombosis in young athletes.

The third factor is hormonal pharmacology. Anabolic-androgenic steroids stimulate erythropoiesis and raise hematocrit, and change the levels of a number of clotting and fibrinolysis factors. Reviews (Pope et al., 2014; Chang et al., 2018) describe cases of thrombosis, heart attacks and strokes in young users of these drugs, although it is difficult to establish the exact magnitude of the risk. Similar considerations apply to erythropoietin and other stimulants of blood formation.

For female athletes, combined oral contraceptives containing estrogens deserve separate attention: they increase the risk of venous thromboembolism, especially in combination with smoking, hereditary thrombophilia and flights. Finally, a coagulogram is mandatory before elective surgery and when anticoagulants are prescribed.

• elective surgery or arthroscopy;
• prolonged immobilization after injury;
• swelling, pain and redness of the lower leg, sudden shortness of breath — an emergency situation;
• frequent bruises, prolonged bleeding from the gums or nose;
• hormonal therapy, taking estrogen-containing contraceptives, a family history of thrombosis;
• monitoring the condition when using drugs that raise hematocrit.

How to prepare and give blood correctly

A coagulogram is extremely sensitive to the conditions of blood collection. Blood is drawn into a tube with sodium citrate, and the ratio of blood to preservative must be exact — an underfilled tube gives falsely prolonged readings. That is why it is important to take the test at a laboratory with an established procedure, not "on the side."

Blood is given in the morning on an empty stomach, after 8–12 hours without food. The day before, it is worth avoiding alcohol and very fatty food, since pronounced lipemia interferes with optical measurement methods. It is advisable not to train intensely in the 24 hours before the test: after a hard workout, fibrinogen, factor VIII and fibrinolysis indicators may temporarily change.

Be sure to tell the doctor about all drugs and supplements. Warfarin, heparins and the new oral anticoagulants directly affect the results. Estrogens, glucocorticoids and hormonal drugs also matter. Large doses of fish oil, aspirin and other anti-inflammatory agents affect platelet function more than the standard coagulogram, but the doctor should know about them.

Another nuance is a very high hematocrit. If it exceeds about 55%, there is less plasma in the sample, and the standard amount of citrate turns out to be excessive. Laboratory guidelines call for adjusting the volume of preservative in such cases, otherwise the clotting time will be artificially prolonged. For athletes with erythrocytosis this is practically important.

The limits of the test's capabilities

The standard coagulogram was created primarily to detect a tendency to bleeding and to monitor anticoagulants. It poorly predicts the risk of thrombosis in a healthy person: normal PT and aPTT do not guarantee that a clot will not form. Separate tests are needed to assess thrombophilia — genetic ones (factor V Leiden, prothrombin mutation) and functional ones.

D-dimer, on the contrary, is sensitive but not specific. It rises after endurance training, injuries, surgery, with inflammation, pregnancy and with age. Therefore a "preventive" D-dimer without symptoms often brings more anxiety than benefit and makes sense only for specific clinical indications.

A single result that slightly exceeds the reference interval rarely has independent significance. The doctor assesses the coagulogram together with the complete blood count, liver tests, a history of bleeding and thrombosis, family history and drug intake. Reference intervals also depend on the specific reagents, so comparing results from different laboratories should be done carefully.

Finally, a coagulogram reflects the state at the moment of collection. If it is needed for monitoring during therapy or when changing a treatment regimen, repeat tests should preferably be taken at the same laboratory, under the same conditions and at the same time of day.

Editorial conclusions

A coagulogram is a tool for assessing the plasma link of blood clotting. Its basic indicators — INR, aPTT and fibrinogen — help detect a tendency to bleeding, impaired liver function and monitor anticoagulant therapy, while D-dimer serves primarily to rule out thrombosis.

For an athlete, the test becomes relevant before surgery, after injuries with immobilization, when taking estrogen-containing contraceptives, with a hereditary predisposition to thrombosis and when using drugs that raise hematocrit. It should be taken on an empty stomach, without intense training the day before, having told the doctor about all drugs.

Symptoms of thrombosis — swelling and pain in the lower leg, sudden shortness of breath, chest pain — require not a scheduled coagulogram but immediate medical attention.

We also recommend reading our materials on what deviations of the coagulogram from the norm mean, on hematocrit and its monitoring, and on a comprehensive examination of an athlete before the season.

References

1. Hoffman M, Monroe DM 3rd. A cell-based model of hemostasis. Thromb Haemost. 2001;85(6):958–965.
2. Wells PS, Anderson DR, Rodger M, et al. Evaluation of D-dimer in the diagnosis of suspected deep-vein thrombosis. N Engl J Med. 2003;349(13):1227–1235.
3. Kearon C, Akl EA, Ornelas J, et al. Antithrombotic therapy for VTE disease: CHEST guideline and expert panel report. Chest. 2016;149(2):315–352.
4. Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.
5. Chang S, Münster AB, Gram J, Sidelmann JJ. Anabolic androgenic steroid abuse: the effects on thrombosis risk, coagulation, and fibrinolysis. Semin Thromb Hemost. 2018;44(8):734–746.
6. Tripodi A, Mannucci PM. The coagulopathy of chronic liver disease. N Engl J Med. 2011;365(2):147–156.